- Email: [email protected]
News update
News update Laser can prevent cavities Cavities in teeth can be prevented through the use of lasers, claim scientists from the University of Rochester. Using very short pulses of lowenergy laser light, experiments have shown a dramatically increased resistance to cavities. However, although promising, the technique has so far only been tested in the laboratory on extracted teeth. More studies are needed before the method is ready for use in dental surgeries. The technique works by instantaneously melting and then fusing a tooth’s enamel coating, making the enamel more chemically resistant to the acids that cause cavities. When the technique is used in conjunction with a fluoride treatment, one experiment showed, cavities were completely stopped. This work is being led by John Featherstone, chair of the Department of Oral Sciences at the Eastman Dental Center and associate professor at the University of Rochester. Working with Wolf Seka, a laser expert at the University’s Laboratory for Laser Energetics and associate professor at the Institute of Optics, Featherstone has been studying the effects of laser
in teeth wavelengths on teeth. The team has collected hundreds of extracted teeth from local dentists, cleaned them, cut them into small pieces, and then exposed them to laser light. They found that light from a pulsed CO2 laser, tuned to 9.3 or 9.6 pm, is almost completely absorbed by the enamel, preventing the light from travelling into the delicate and sensitive pulp of the tooth, where it would cause damage. The team used about 25 100~ps pulses to heat the surface of the enamel up to 1000°C in a fraction of a second. The heat momentarily melts the crystalline structure, knocking out some of the decay-prone carbonate molecules in the tooth. When the enamel fuses, it is claimed to be 70% to 85% more resistant to acids. Whereas calcium phosphate-the major mineral in tooth enameldissolves very slowly in acid, the carbonate that replaces some phosphate molecules when teeth are formed, dissolves very easily in acid-so leaving the teeth prone to cavities. According to John Featherstone, ‘It’s a delicate balance. You want
one of the team working with John Featherstone and Wolf Seka at the University of Rochester, uses a laser to heat and anneal teeth, to investigate how this affects their resistance to cavities. The computer monitor plots the temperature of the tooth as it heats up and cools. Picture by James MontanusllJniversity of Rochester
0030-3992/95/$10.00 Optics & Laser Technology Vol 27 No 3 1995
@ 1995
Elsevier Science.
enough heat to anneal the tooth, but obviously you don’t want to damage the pulp.’ Wolf Seka added, ‘To heat the tooth several hundred degrees without endangering the interior, you need a laser with a short pulse duration. We use very little energy to heat the tooth; each pulse is about 100 mJ.’ To test the effect of laser treatment, John Featherstone duplicates, for a two-week period, the daily cycle that teeth go through in the mouth. He puts them in an acid bath for seven hours (to mimic the acids created as we eat during the day) and puts them in a saliva-like solution for 17 hours to bathe the teeth in nutrients and minerals, re-mineralizing them. Then the team compares the amount of mineral loss from the laser-treated to non-treated teeth, which indicates resistance to cavities. Both Featherstone and Seka emphasize that there is a lot more work to do. They believe the effect will last for many years, but they will not know until they have run further tests. University of Rochester, Rochester, New York 14627-0033, USA. Fax: +I 716 275 0359 0
Eurolaser
training
in 1995
This year’s Eurolaser training courses will be held at the Technical University of Vienna, Austria, with the first module running from 2-14 October, and the second module from 16-25 October. High-power lasers can perform various manufacturing processes with significant economic and production advantages over existing conventional methods. Successful application of these processes can lead to improved competitiveness and profitability. Consequently, the principal objective of the Eurolaser University Training Partnership (UETP) is to provide training in this laser technology-training that is tailored specifically to the requirements of European industry at both engineer and management levels. The Eurolaser Academy is the
All rights reserved III
News update formal graduate training division of the Eurolaser UETP and, in order to make the training accessible to students over as wide an area as possible, it was one of the original goals of the Academy to move the venue around suitable laser processing centres of excellence. Indeed this has remained the basic policy in selecting host countries. In the first academic year, 1993, the host institution was the Fraunhofer Institut fur Lasertechnik in Aachen, Germany. This was attended by approximately 35 students from 11 European countries. In the second year, a similar number of students attended a multivenue Eurolaser Academy hosted and organized in the UK by the Cambridge-based joining research institute TWI, utilizing the facilities of AEA Technology and Liverpool University. Now in its third year, the host institution is to be the Technical University of Vienna in Austria. Many of the lectures and all of the hands-on practicals will take place at the University’s Institute for High Power Beam Technology, which is led by Professor Dieter Schuocker, Director of the Eurolaser Academy. In an innovative departure from previous years, this year’s Eurolaser Academy will benefit from two complementary modular approaches to laser training. The first module (214 October) will concentrate on process and equipment fundamentals. The approach will be formal and intensive, with equal time being allocated to lectures and practicals. Topics covered will include the basics of contemporary industrial lasers (CO2 and Nd : YAG), the most significant processes (welding, cutting, surface treatment), material and workpiece classification, health and safety, basic interactions, beam propagation and computer numerical control. The second module (16-25 October) is in ‘seminar style’ and consists of interactive professional seminars on leading edge topics complemented by laboratory workshops, industrial visits and company presentations.
The rationale for using this style of module is twofold. First, it acclimatizes the students to the way that many scientific/technical events actually happen. Secondly, it addresses a requirement to open up the Academy to those who wish to attend for maybe one or two days but are unable to attend for the whole of one or two modules. Topics covered will include excimer lasers and their applications, semiconductor lasers and their industrial possibilities, laser forming, assessment of competing technologies, European laser research and process modelling. Students attending both modules and passing an optional examination are awarded the qualification of European Laser Engineer from the Technical University of Vienna. Discussions are currently under way with the European Welding Federation with a view to incorporating the Eurolaser Academy course as a recognized laser endorsement to the established qualification of European Welding Engineer. The UETP is also active in promoting the uptake of laser technology through a number of short courses, usually lasting two or three days and targeted at those working in industry. Titles include, ‘State of the art in materials processing’, ‘Laser safety in materials processing’, ‘Laser welding processing technology’ and ‘Laser processing, a manufacturing manager’s guide’. In addition, there is an individual mobility and training scheme, and information services such as Eurolaser News and Eurolaser Bulletin Board Service. The Eurolaser Academy was set up to help industry through advanced postgraduate training in the fields of laser and materials processing technology. Originating from an initiative by the Eurolaser Government Coordination Committee in 1991, and supported by the COMETT Programme of the Commission of the European Union, the Eurolaser Academy provides an intensive, modular, fourweek course in industrial laser technology designed to augment the skills
of qualified engineers and physicists through a balanced combination of lectures, practicals and tutorial work. Those who benefit immediately from the training are predominantly graduates in the fields of mechanical production and electrical engineering, physicists or those in related numerate disciplines, and existing engineers already qualified by the ECCW. The ultimate beneficiary will be European industry, which should benefit in the medium to long term through improved productivity and profitability. Eurolaser Academy, c/o Igor Arbanas, Mostgasse 3, A1040 Vienna, Austria. Fax: +43 1 586 1780 0 Eurolaser Academy (UK), cfo Roger Crafer, Abington Consultants, 78 High Street, Abington, Cambridge CBl 6AE, UK. Fax: +44 1223 891 576 0
Centre for manufacturing cylindrical lenses In response to strong and growing OEM demands, Melles Griot has announced a major expansion of its cylinder lens manufacturing capabilities with the opening of a new Cylinder Lens Manufacturing Centre in the USA. The new facility manufactures both positive and negative cylindrical elements, from 3 mm to 510 mm long, to precision tolerances and tight cosmetic specifications. The Centre is also able to fabricate more unusual optics, such as cylindrical rods, wedged cylinders and cylinders made from unusual optical glasses. The company now has over 35 specialized machines for cylinder lens fabrication, with a capacity exceeding 10,000 lens elements per month. Melles Griot also offers a complete range of cylinder coating capabilities, including multilayer, anti-reflective and reflective coatings. Melles Griot Ltd, Brookmount Court, Kirkwood Road, Cambridge CB4 2QH, UK. Fax: +44 (0)1223 425310
0 Optics
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& Laser Technology Vol 27 No 3 1995
News update Laser power
and position
Non-invasive in-line monitoring of high-power CO2 lasers can be carried out with the BM 10.6 Beam Monitor, developed by Precision-Optical Engineering. Claimed to be the first system to offer a safety interlock, the unit can also be used in system alignment, giving a maximum output when the beam is correctly aligned. In the past, in-line monitoring of high-power laser beams, especially for safety procedures, has proved difficult, Methods using components such as beam-splitters have been used, but these can be unreliable, as the components’ characteristics could change as a result of the high intensity beam being used. For safety monitoring of beams, often only passive systems are used, effectively relying on an operator spotting the results of a stray beamthat is, smoke or burning-before the laser could be switched off. The recently launched beam monitor, however, is an active component and can act as an in-line, intrinsic power and position safety monitor. In effect, the monitor samples a very small fraction of the beam (- O.OS%), through which changes of 0.5% of the incident power can be detected. Thus, if there is a fluctuation in power-for example, if the beam is moved out of alignment or, for some reason, it is being interrupted-the system will monitor
safety
monitor
works
in-line Fold
Used as a final fold monitor can provide system
mirror in a beam delivery line, Precision-Optical Engineering’s beam an indication of beam power stability at the output of a processing
this and switch off the laser. The main component is a specially developed diamond machined mirror. This has been machined by PrecisionOptical Engineering to diffract a specific proportion of the beam at a specific angle. In the CO;! monitor, the 10.6 urn beam has about 0.01% diffracted into a thermopile detector. Changes of 0.5% can be detected through this method ensuring high
sensitivity and a 40 ms response time. Designed and manufactured by Precision-Optical Engineering, the mirror is made from OFHC copper and is water cooled to allow a wide range of beams up to, for example, 10 kW. Beams up to 45 mm diameter can be accommodated, making the unit suitable for a wide range of applications including: safety interlock beam power stability 0 system alignment l beam wander alarm l backscatter monitor 0 process monitoring l l
Having no moving parts, the beam monitor is a low maintenance unit, which can be used with most laser/ electronic control systems for laser processing machines. It interfaces easily to most control systems. The heart of Precision-Optical Engineering’s CO 2 laser beam monitor is the sampling mirror, which has been diamond machined to produce first-order diffraction thermopile detector
Optics & Laser Technology Vol 27 No 3 1995
copper into a
Precision-Optical Engineering Ltd, 42 Wilbury Way, Hitchin, Hertfordshire SG4 OTP, UK. Fax: +44 (011462 440329 0
V
News update Market
forecasts
for industrial
Spurred on by new applications, improving technologies and demand from new regions, worldwide sales of industrial and scientific laser systems will grow from $1.4 billion in 1993 to $2.25 billion in the year 2000, according to a study recently released by Frost & Sullivan. The report, Industrial and Scientific Lasers: Industrial Sales Lead Resurgence in Growth, states that, in 1993, CO2 lasers accounted for 45% of market revenues, solid-state lasers 26%, diode lasers 16% and ion lasers 6%. Over 90% of this combined market is accounted for by industrial applications, which are growing more rapidly than scientific ones. However, lasers have also established themselves as prime equipment for many scientific applications-most notably spectroscopy. New capabilities with faster repetition rates and wider wavelength range are continuing to aid the spread of lasers in the scientific community. The report states that there will be an increasing shift towards selling lasers in new areas of the world, including China, the former Soviet Union and eastern Europe, and numerous parts of the Third World. With the Japanese laser market starting to mature in several segments, Total industrial and scientific laser systems market: unit shipment and revenue forecasts (world) 1990-2000 according to Frost & Sullivan
Year
Units (Million)
1990 42.5 1991 46.2 1992 50.4 1993 55.0 1994 60.4 1995 66.8 1996 73.0 1997 80.1 1998 88.1 1999 97.4 2000 107.9 Compound annual 2000) = 7.0%
Revenues ($ billion)
Revenue growth rate (%)
1.31 1.33 1.34 1.41 1.51 1.62 1.73 1.85 1.98 2.11
1.7 0.3 5.3 7.3 7.3 6.9 6.8 6.9 6.8
2.26
6.7
growth rate (1993-
lasers
growth in China and Korea may increasingly lead Pacific Rim growth. Diode lasers have increased their penetration, taking over the barcode scanning market and establishing themselves in optical storage and printing applications. Tunable solidstate lasers, Frost & Sullivan believe, have established themselves as a force in the scientific market, with their ease of operation and performance making them preferable to more traditional tunable lasers. Advances in new laser varieties have meant declines for other segwith HeNe lasers losing ments, markets with the proliferation of diode lasers, and dye lasers losing heavily in the scientific market with the advance of tunable solid-state lasers. In materials processing applications, competition between CO2 and solid-state laser systems has increased in the last few years as it has between Nd : YAG and excimer lasers. The global market, the report states, has seen unprecedented price competition and aggressive marketing both between manufacturers of the same media and between different media. Competition will intensify, increasingly pressing profit margins. While the market will continue to grow, Frost & Sullivan believe, it remains strongly susceptible to cyclical recessions. Consolidation has progressed in response to globalization and the early 1990s’ market slowdown. Those lasers with the largest sales will see the most gains in new capabilities and performance as stronger sales lead vendors to put more resources into R&D and therefore increased functionality. Advances through the remainder of the decade, the report states, will include the development of new laser media-particularly in the tunable solid-state and diode laser markets; development of higher-power lasers generally, especially in the industrial CO*, diode, excimer and solid-state
laser market; development of lasers with higher repetition rates, particularly in solid-state markets, and development of direct-output blue solid-state lasers and blue/green diode lasers with outputs under 543 nm. The report is priced at $1895. Frost & Sullivan, 2525 CharLeston Road, Mountain View, California 94043, USA. Fax: +1 415 961 5042 Frost & Sullivan, Sullivan House, 4 Grosvenor Gardens, London SW1 W ODH, UK. Fax: i-44 (171) 730 3343
0
Fibre-optic spacecraft monitor to be developed Mission controllers of orbiting spacecraft, in the past, have had to rely on binary microswitches-which were often unreliable-to tell them whether on-board deployment mechanisms had operated or not. Now, the European Space Agency (ESA) has asked Sira to solve this problem by designing a low-cost, totally passive, but highly flexible fibre-optic spacecraft monitoring system. ESTEC, ESA’s technical research arm, has awarded Sira a feasibility contract to investigate how such a system could be designed with minimal installation and power requirements, yet be capable of providing a clear picture of whether six or more critical deployment or scanning mechanisms have been accurately deployed. According to Sira’s Dr Mike Cutter, the task will involve an assessment of the feasibility of optically multiplexing six or more optical-fibre transmitted images to one or more smart sensors with on-chip processing capability. He said, ‘The beauty of a passive fibre-optic system is that it can be fitted after the spacecraft has been assembled with minimal concern for interface issues such as electromagnetic interference.’ There will be a single central image-acquisition and processing unit with the ability to select which sensor Optics
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& Laser Technology Vol 27 No 3 1995
News update to view, what time resolution to use and the most appropriate data rate. This unit will be the only powered part of the system and will be capable of storing data and transmitting it to the ground. Smart sensors with on-chip processing capability will be required to carry out some data reduction. Although each sensor will have a fairly low resolution of 256 x 256
pixels, this still represents a large amount of data, even at a low data rate. The sensors will have to be capable of observing deployment from close to the spacecraft out to a distance of about 6 m and provide a reasonable focused image over the range. Sira Ltd, South Hill, Chislehurst, Kent BR7 .5EH, UK. Fax: i44 (0) 181-467 6515 0
Lenses for image processing Designed for use in image processing, a range of high-quality lenses has been introduced by Rodenstock. The Magnagon lenses are suitable for use in image processing applications, in conjunction with electronic image scanners, where high demands are made on the optical imaging quality. The first lens to be introduced in this range was the Magnagon CCD 4.0/75 mm, which is claimed to give exceptional quality over a wide scale range.
The Magnagon
range
applications
The principal lens are
characteristics
of this
0 very low flare free of vignetting for the entire magnification scale l low longitudinal chromatic aberration a high-quality, independent of the magnification used l
Opt&he Precision strasse 43, many. Fax:
Werke G Rodenstock, Optics Division, IsarD-80469 Munich, Ger0 f49 89 7202 141
of CCD lenses is available from Rodenstock
lnterferometric
research in ophthalmology --
Research work in the Institute of Physics at the Technical University of Wroclaw, Poland, is currently dealing with the application of interferometric methods in ophthalmology. Dr Henryk Kasprzak and his team are co-operating with an Eye Clinic to develop some new measurement
techniques that can be applied in ophthalmic practice. One study, for example, has performed in vivo analysis of the dynamic changes of the cornea1 contour to a submicrometre accuracy by using interferometric methods. In this work, a Twyman-Green interferometer was used for the
analysis of the wavefront reflected from the human cornea in vivo. The analysed wavefront interfered with the reference one and produced a rapidly moving fringe pattern related to the motion of the eyelid. The rapidly moving fringes were recorded on videotape and sequences of frames from the videotape, delayed by 40 ms, were stored and processed. The fringe patterns were numerically analysed and three-dimensional plots of the cornea1 contour were determined. Numerical subtraction of every two neighbouring three-dimensional plots created a sequence of new contour representing maps, changes in the cornea1 geometry within each 40 ms time period. The three-dimensional plots of the differences of cornea1 contours obtained from the neighbouring frames of the videotape show that the cornea does not behave as a rigid body in the fast motion of the eyelid but deforms and varies its topography in time. Another experiment studied, using in vivo interferometric examination, the human tear film and also observed the kinetics of different forms of the tear film’s irregularities. In this study, a human eye was inserted in one arm of the TwymanGreen interferometer, and a HeNe laser was used as the light source. The interference of the wavefront reflected from the cornea1 tear film, with the reference wavefront, produced a rapidly moving fringe pattern, disturbed by irregularities in the tear film. The observed image of the fringe pattern was recorded on a video recorder with a CCD camera. The selected frames from the videotape were stored and processed in a PC computer. The rapidly moving fringe pattern showed an irregular form shortly after an eye blink, after which the irregularity of the tear film reduces after about 3-5 s. After that time, the cornea1 surface becomes more and more smooth. However, when the eye remains open, an increase in fringe irregularity can be seen. After about 30 s from the last blink, the fringes are extre-
Optics & Vol 27
Laser Technology No 3 1995
vii
News update mely irregular, due to the drying of the tear layer and the roughness of the cornea1 surface. It is claimed that the types of observed irregularities of the tear film can be divided into four groups. Dr Henryk Kasprzak, Institute of Physics, Technical University of Wroclaw, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland. Fax: (0048 71) 22 96 96 0
System for high-precision laser machining Specifically designed to machine tiny objects with high precision, the Laserlith system has been developed by Advanced Recording Technologies (ART). With the laser-based micromachining station, rings and gears less than 0.002 inches (N 0.05 mm) in diameter can be made from a variety of materials. In addition letters only 0.006 inches (N 0.15 mm) high can be clearly scrolled out. According to the company, the high precision is attained through the use of a highly stable cultured granite housing, coupled to laser controlled interferometer stages. In addition, to attain high reliability, the system uses diode-pumped YAG lasers rather than the more conventional krypton arc pumped systems. The system has an accuracy of up to 0.25 pm, a speed up to 8 inches per second (-203 mm ssl ) and kerf widths to 0.5 l.rrn. Applications for the system are thought to include the precision micromachining of ceramics, metals and glasses, such as ferrite, aluminium oxide, calcium titanate, stainless steel, aluminium titanate carbide and silicon carbide. Many types of lasers can be installed in the system, including diode pumped YAG and YLF, Qswitched, mode locked, doubled, nitrogen, pulsed or tripled, C02, continuous lasers. Advanced Recording Technologies, 1310 Industrial Avenue, Escondido, C$it;;ja 92029, USA. Fax: +1619 0
Laser micromachining A micromachining system has been developed by Cambridge Consultants Ltd (CCL) for the Defence Research Agency (DRA). The system was delivered to an exacting time scale and specification and is being used for the ultraviolet optically assisted etch of ceramic infrared electro-optic chips, such as those used in high resolution, room temperature, infrared imaging devices. DRA’s original system used one laser beam to cut microscopic grooves, which form the individual detector elements that together comprise the image sensing array. This proved to be time consuming and restricted to smaller, lower resolution arrays. CCL developed a system that simultaneously generated five focused laser beams so that five grooves were machined in parallel. This process enabled larger arrays to be manufactured at five times the speed. The specification was exacting, but CCL’s specialist skills in optical engineering ensured that the lasers conformed to an ultra-precise geometry and were also very closely matched in power and spot-size to enable each groove to be machined at
Arrays can be manufactured speed laser micromachinery
system has high speed the same rate. By drawing on skills in system design and optical engineering, CCL was able to meet all the key performance demands. The system uses an array of beam-splitting and conditioning elements to generate an angular array of beams that are focused by a custom ultraviolet objective. A novel use of optical retarders enables loss-free power balancing and contributes to a very high overall efficiency in excess of 75%, allowing a 3 W laser to be used in future systems and achieving considerable savings. Through a combination of precision machining, interferometric prealignment and the subtle use of ‘optical-levers’, the system is simultaneously robust and stable whilst being very simple to bring into precise alignment. In consequence, although no testing was possible until integration with the high-power laser at DRA, successful cutting was achieved on the first attempt. Cambridge Consultants Ltd, Science Park, Milton Road, Cambridge CB4 4DW, UK. Fax: +44 (O)I223 423373
at five times the speed of original equipment devetoped by CCL
equipment
Optics VIII
with the high-
& Laser Technology Vol 27 No 3 1995
Fibre-optic
system finds use underground
A Distributed Temperature Sensing (DTS) system from York Sensors is being used to monitor Underground Coal Gasification (UCG) in a European trial being carried out by a partnership of Spanish, Belgian and British companies with European Community support. The in situ conversion of coal into gas will be attempted by Underground Gasification Europe AEIE (UGE) in a 600 m deep seam of black lignite in the province of Teruel in the north-east of Spain. In the project, three types of well are drilled into the coal seam. Injection wells are used to ignite the coal and to carry oxygen to the seam; a production well recovers the gas and monitoring wells assess the development of the gasifier. In practice, the process is more complex and, in reality, operates like an underground chemical reactor at high temperature and high pressure. With further refinement, some researchers believe that within 20-30 years UCG technology could be used to recover gasified coal from closed pits. York’s distributed temperature sensing system is coupled to a specially designed fibre-optic cable to withstand the harsh environment and will monitor the reactions continuously. It will provide distributed measurements of temperature each metre down the length of the wells. From these measurements UGE can monitor the temperatures of the reaction zones, which can reach 1100°C. Traditional temperature measurement devices will also be used but cannot compete with the amount of data that can be generated from a singe sensor cable. Cavity growth-that is, how much of the coal seam is being convertedwill also be monitored using the DTS system by measuring how much of the sensor is destroyed as the combustion zone progresses through the seam. York Sensors’ DTS system has already been successfully tested by companies, including British Coal, Optics & Laser Technology Vol 27 No 3 1995
National Grid and Copenhagen Energy, to provide a cost efficient means of monitoring reactions through temperatures. The DTS System consists of the following. l
l
l
An instrument containing an OTDR (Optical Time Domain Reflectometer), coupled to a microprocessor controlling signal processing in real time. One to six sensors each up to 10 km long, consisting of loops of standard telecommunications-grade multimode optical fibre. DTS Manager, a Windows application running on a 386 or 486 PC.
A typical installation of 4 km sensor cable can provide up to 16000 points of temperature versus
Stepper
York UGE tion. head box
used by gasijica1 welljunction
distance information to a resolution better than 1°C. These data can be updated every few seconds or several minutes apart. The spatial resolution is 1 m. York Sensors Ltd, York House, School Lane, Chandlers Ford, Eastleigh, Hampshire SO53 4DG, UK. Fax: 01703 267234 0
lens manufacturing
Carl Zeiss is nearing completion of a three-year, $37-million expansion programme that will increase its manufacturing capacity in stepper lenses to keep pace with the highvolume demand of its leading customer for microlithography optics, ASM Lithography (ASML). The expansion, scheduled to be completed by the second quarter of 1995, will enable Carl Zeiss to increase its stepper lens production to more than 200 units per year, matching ASML’s annual capacity in stepper systems. The strategic partnership between Carl Zeiss and ASML began in 1989, when the companies established common policies involving product strategy, technology development and quality assurance. Carl Zeiss’ experience in developing microlithography systems dates back to 1972 with optics for 1:l photorepeaters. ‘Today, our microlithography lens division reinvests more than 30% of its revenues to fund continuing research and development work and to meet the increasing market demands for stepper lenses’, said Dr Dieter
Sensors’ DTS system is being to monitor underground coal Shown here is Injection Well and the optical fibre cables’
improved
Kurz, director of optical lithography components with Carl Zeiss. ‘This latest expansion continues our strong commitment to advancing microlithography optics technology.’ ASM Lithography, 2315 West Fairmount Drive, Tempe, Arizona 85282, USA. Fax: +1 602 0793 0
Radiometric and photometric measurements described Light measurement instrumentation, applications and the basic concepts of radiometry and photometry are described in a catalogue available from International Light. It describes thousands of contigurations and combinations of systems for performing radiometric and photometric measurements. Developed for those involved with light measurements-regardless of their level of expertise-this expanded catalogue includes applications, tutorials, spectral graphs and spatial information. International Light Inc, 17 Graf Road, Newburyport, Massachusetts 01950, USA. Fax: fl 508 462 0759
ix
News update Improved
assembly
for rectilinear
A special assembly process has been developed by Rodenstock for rectilinear lenses. Rectilinear lenses are used in scanners where, owing to the reduced size of the lens, more compact system designs are possible. In addition, owing to the minimized dimensions, the production of the lenses allows a much higher loading per polishing tool than in round lens production. Thus, valuable polishing time can be saved. While, in traditional lens construction, the lens elements and their mounts require surfaces to determine the position that is to be worked, with very tight tolerances; in Rodenstock’s system, the function of these surfaces can be dispensed with.
lenses
The lenses-whose edges can be of any shape-are positioned exactly using an air-cushioned rotating stroke spindle in conjunction with a positional sensor for the optically effective surfaces outside the lens housing. Only then are the aligned lenses moved to the final position in the mount housing in a program-controlled process. The lenses are fixed in position with a tolerance of 0.001 m, using a patented cementing process. The mount housing has only a holding function and, like the edging surfaces of the lens, can be produced using only very rough tolerances. With rectilinear lens technology, the precision stands and falls with the special equipment used, the assem-
bly, and the assembly process. This precision is copied into the lens element by element. It therefore does not need to be generated by extremely tight production tolerances. A further advantage of rectilinear lens technology when used in scanners, is the miniaturizing of the scanning lens. As the deflection element of the output scanner can be moved closer to the lens, a further degree of freedom is obtained for correction (distance of pupil to lens). With a short pupil distance, the lens diameter is also automatically reduced and, in a number of cases, the lens can have a smaller design than a lens with a round shape. Optische Werke G Rodenstock, Precision Optics Division, Isarstrasse 43, D-80469 Munich, Germany. Fax: +49 89 7202 141 0
Improved manufacturing means fewer trace elements in quartz glass Quartz glass with fewer trace elements has been developed by Heraeus. The company’s quartz glass manufacturing technology eliminates most heavy metals and other impurities from its raw quartz materials. Compared with standard semiconductor quartz glass grades, the recently developed HSQ 351 (standard) and HSQ 751 (improved quality) significantly reduce the migration of trace elements (like alkali and heavy meals) to the wafers. Thus, wafers are protected against minority carrier lifetime degradation, which is a serious indicator for upcoming yield problems. Application studies about the interaction of quartz glass and silicon wafers show about 50 to 100 times less heavy metals in the bulk of the wafers processed with HSQ 351 or HSQ 751. Additionally, the quality of the surfaces, with respect to saucer pits and oxidation stack faults, was substantially higher. Rodenstock’s assembly process for rectilinear lenses. At the bottom of the figure can be seen the rotating stroke spindle (which was produced in-house due to the high demands on its precision) with the rectilinear lens in place. At the top, the jig for the mechanical housing can be seen. Once the lens has been aligned on the spindle, it is moved into the mount from below
X
Heraeus Quarzglas GmbH, SemiDivision, D-63801 conductor Kleinostheim, Germany. Fax: +49 6027 507 278 0 Optics & Laser Technology Vol 27 No 3 1995
Is your safety equipment up to the European Union CE mark? It will be illegal, from 1 July this year, for manufacturers to sell new eye and face protective equipment that does not carry the European Union CE mark. In addition, the same legislation applies to other items of personal protective equipment including ear defenders, safety helmets, respirators etc. However, the CE mark in itself is not a European standard it is an indication that the product meets the requirements of the Personal Protective Equipment (PPE) Directive which is now part of UK law. A European standard, EN 166, which will bring about a uniform technical specification throughout the Union, is expected to be published later this year. Convenor of the ELI’s technical committee working group on industrial eye protection, David Yelland, said ‘The CE mark is an important stage in assisting free trade between member states. Products carrying the mark will be recognized in all countries. but we still have to finalize EN 166. Until we do so, manufacturers can obtain their CE mark by demonstrating product conformance with existing national standards or the draft European standard, prEN 166.’ ‘Progress towards agreeing a technical standard across the European Union has been painfully slow.’ David said, ‘With countries believing their own requirements to be satisfactory. This has meant that international trading has been hampered by the need to have approval for each country.’ ‘Now we are making headway, and the introduction of the CE mark is significant. Eventually, when EN 166 is approved and published, all eye and face protective equipment will have to meet its standards, which I see as an amalgam between the UK’s BS 2092 and the German DIN requirements.’ ‘For British producers this will not be much more stringent than BS 2092, but it will contain additional optical requirements and introduce new marking symbols for impact resistance, molten metal protection etc.’ Although the regulations relating to the CE mark finally take effect this summer, unmarked products already in the supply line before 1 July can still be issued and used for their normal, serviceable life. From that date some items will carry both the CE and BS markings. David Yelland said, ‘This is perfectly legal as the new legislation does not specify the technical standard to which the CE certification is obtained.’ Manufacturers believe they have won a victory over bureaucrats in Brussels who originally also wanted the year of testing to be included as an integral part of the CE mark.
Optm
David, who is also Group Technical Director of Pulsafe Safety Products, said, ‘Annual changes would require expensive changes in marking plates and now it seems certain the suggestion will be dropped.’ He added, ‘The form of the CE mark itself depends on the product category and will be changed again after January 1997 in order to harmonize PPE products with others.’ According to David, ‘The best advice for purchasers and end users concerned with category two and three products over the next two years is to look for the CE mark and the four-digit number of the notifying body.’ If the latter is not there, questions should be asked, as the four-digit number is optional on category two products but mandatory on category three items.’ Effectively, PPE category one products are of simple design and would involve only minor, reversible user harm should they fail. Category two products are of intermediate design where failure could cause serious permanent injury, while category three products are of complex design where failure could cause fatality. Under the CE regulations, category one products can be self-certificated, while type testing by a Notified Body is required for category two. For category three products to be approved there has to be type testing by a Notified Body plus ongoing certification either through annual repeat testing or by means of BS5750jISO 9000 accreditation. David Yelland warned that some manufacturers are already offering products marked EN 166. ‘This cannot be correct. There is no such thing as EN 166, and the products should be properly marked prEN 166 which indicates that they have met the requirements of the draft European standard.’ ‘But the question then is, “which draft?“, because there have been three versions since CE certification began, and the latest of these has different marking symbols compared with the first two.’ David explianed his own compnay’s position, ‘It is because the goalposts were shifting so frequently that at Pulsafe we decided to obtain our CE marking approval on the basis of BS 2092.’ ‘That decision could be seen as being anti-European or retrogressive,’ he said, ‘But the pitfalls of using a nonproven draft standard were too great to ignore. If products were approved to prEN 166 then each time the draft was updated and/or the marking symbols changed the customers would need to be re-educated on their meanings.’ ‘With such changes in markings there could be apparently identical products on the market with marking symbols having fundamentally different meanings.’ He added, ‘Approval to draft standards is a potent recipe for total confusion.’ The eye and face protective sector is not the only part of the PPE industry where EN standards have not yet been finalized. Manufacturers of air-fed respirators,
& Laser Technology
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XI
News certain types of gloves and ear defenders are still awaiting announcements, but they will all have to use the CE mark from 1 July. So, does the arrival of the CE mark in the market place mean the-end of the UK Kitemark? David said, ‘The Kitemark will have just as much relevance as it did before the introduction of the CE mark. They are two totally different entities. One cannot replace the other, but they can co-exist.’ He contined, ‘The Kitemark is a quality indicator. The CE mark is a legal rubber stamp. The CE mark is not a substitute for the Kitemark, and was never intended to be so.’ He added, ‘The Kitemark is a much more rigorous scheme than the CE mark. The CE mark, once awarded, never has to be independently verified thereafter, whereas the Kitemark is subject to continuous scrutiny.’ ‘I suggest that customers look for both marks the CE because it is a legal requirements and the kite because it gives independent third party assurance of continuing product conformity.’ ‘Apart from the obvious advantages, this could carry weight in the event of product liability claims.’ The Kitemark is quite expensive to maintain and there may be some manufacturers who take the opportunity to drop it during the confusion surrounding the introduction of the CE mark.
Update
‘The fate of the Kitemark is in the hands of the purchaser and end user. It will continue as long as it is in demand and providing no one is fooled into believing that it has been replaced by the CE mark.’ ‘Manufacturers who have adopted the perilous route of draft European standards could find the Kitemark denied them as BSI will not offer Kitemark schemes to draft standards.’ UK regulations arising from the European PPE product and workplace directives are enforced by trading standards officers and HSE (Health and Safety Executives) factory inspectors respectively. Said David Yelland, ‘The most important obligation falling on employers under the PPE at Work Regulations is the responsibility for selecting suitable personal protective equipment for staff.’ ‘That responsibility cannot be passed off to the manufacturer whose duty is to provide information concerning product performance.’ ‘The establishment of common European product standards and workplace regulations has been a long drawn out process and has led to a great deal of confusion and misunderstanding. But now the task is almost complete and it must be hoped that the intended benefits to worker safety and pan-European trading practices will begin to be realized in the months ahead.’
Research institutions, universities and companies with news and laboratory reports they wish to have included in the news update sections of Optics & Laser Technology should contact the managing editor at the address given below. Details of current projects and research work which would interest the international readership of Optics & Laser Technology are welcomed.
Nick Butler, Managing Editor Elsevier Advanced Technology Optics & Laser Technology
PO Box 150, Kidlington Oxford OX5 1AS, UK Tel: + 44 (0)1865 843677 Fax: + 44 (0)1865 843971
ELSEVIER ADVANCED
TECllNOLOGY
Optics xii
& Laser Technology Vol 27 No 3 1995
in teeth wavelengths on teeth. The team has collected hundreds of extracted teeth from local dentists, cleaned them, cut them into small pieces, and then exposed them to laser light. They found that light from a pulsed CO2 laser, tuned to 9.3 or 9.6 pm, is almost completely absorbed by the enamel, preventing the light from travelling into the delicate and sensitive pulp of the tooth, where it would cause damage. The team used about 25 100~ps pulses to heat the surface of the enamel up to 1000°C in a fraction of a second. The heat momentarily melts the crystalline structure, knocking out some of the decay-prone carbonate molecules in the tooth. When the enamel fuses, it is claimed to be 70% to 85% more resistant to acids. Whereas calcium phosphate-the major mineral in tooth enameldissolves very slowly in acid, the carbonate that replaces some phosphate molecules when teeth are formed, dissolves very easily in acid-so leaving the teeth prone to cavities. According to John Featherstone, ‘It’s a delicate balance. You want
one of the team working with John Featherstone and Wolf Seka at the University of Rochester, uses a laser to heat and anneal teeth, to investigate how this affects their resistance to cavities. The computer monitor plots the temperature of the tooth as it heats up and cools. Picture by James MontanusllJniversity of Rochester
0030-3992/95/$10.00 Optics & Laser Technology Vol 27 No 3 1995
@ 1995
Elsevier Science.
enough heat to anneal the tooth, but obviously you don’t want to damage the pulp.’ Wolf Seka added, ‘To heat the tooth several hundred degrees without endangering the interior, you need a laser with a short pulse duration. We use very little energy to heat the tooth; each pulse is about 100 mJ.’ To test the effect of laser treatment, John Featherstone duplicates, for a two-week period, the daily cycle that teeth go through in the mouth. He puts them in an acid bath for seven hours (to mimic the acids created as we eat during the day) and puts them in a saliva-like solution for 17 hours to bathe the teeth in nutrients and minerals, re-mineralizing them. Then the team compares the amount of mineral loss from the laser-treated to non-treated teeth, which indicates resistance to cavities. Both Featherstone and Seka emphasize that there is a lot more work to do. They believe the effect will last for many years, but they will not know until they have run further tests. University of Rochester, Rochester, New York 14627-0033, USA. Fax: +I 716 275 0359 0
Eurolaser
training
in 1995
This year’s Eurolaser training courses will be held at the Technical University of Vienna, Austria, with the first module running from 2-14 October, and the second module from 16-25 October. High-power lasers can perform various manufacturing processes with significant economic and production advantages over existing conventional methods. Successful application of these processes can lead to improved competitiveness and profitability. Consequently, the principal objective of the Eurolaser University Training Partnership (UETP) is to provide training in this laser technology-training that is tailored specifically to the requirements of European industry at both engineer and management levels. The Eurolaser Academy is the
All rights reserved III
News update formal graduate training division of the Eurolaser UETP and, in order to make the training accessible to students over as wide an area as possible, it was one of the original goals of the Academy to move the venue around suitable laser processing centres of excellence. Indeed this has remained the basic policy in selecting host countries. In the first academic year, 1993, the host institution was the Fraunhofer Institut fur Lasertechnik in Aachen, Germany. This was attended by approximately 35 students from 11 European countries. In the second year, a similar number of students attended a multivenue Eurolaser Academy hosted and organized in the UK by the Cambridge-based joining research institute TWI, utilizing the facilities of AEA Technology and Liverpool University. Now in its third year, the host institution is to be the Technical University of Vienna in Austria. Many of the lectures and all of the hands-on practicals will take place at the University’s Institute for High Power Beam Technology, which is led by Professor Dieter Schuocker, Director of the Eurolaser Academy. In an innovative departure from previous years, this year’s Eurolaser Academy will benefit from two complementary modular approaches to laser training. The first module (214 October) will concentrate on process and equipment fundamentals. The approach will be formal and intensive, with equal time being allocated to lectures and practicals. Topics covered will include the basics of contemporary industrial lasers (CO2 and Nd : YAG), the most significant processes (welding, cutting, surface treatment), material and workpiece classification, health and safety, basic interactions, beam propagation and computer numerical control. The second module (16-25 October) is in ‘seminar style’ and consists of interactive professional seminars on leading edge topics complemented by laboratory workshops, industrial visits and company presentations.
The rationale for using this style of module is twofold. First, it acclimatizes the students to the way that many scientific/technical events actually happen. Secondly, it addresses a requirement to open up the Academy to those who wish to attend for maybe one or two days but are unable to attend for the whole of one or two modules. Topics covered will include excimer lasers and their applications, semiconductor lasers and their industrial possibilities, laser forming, assessment of competing technologies, European laser research and process modelling. Students attending both modules and passing an optional examination are awarded the qualification of European Laser Engineer from the Technical University of Vienna. Discussions are currently under way with the European Welding Federation with a view to incorporating the Eurolaser Academy course as a recognized laser endorsement to the established qualification of European Welding Engineer. The UETP is also active in promoting the uptake of laser technology through a number of short courses, usually lasting two or three days and targeted at those working in industry. Titles include, ‘State of the art in materials processing’, ‘Laser safety in materials processing’, ‘Laser welding processing technology’ and ‘Laser processing, a manufacturing manager’s guide’. In addition, there is an individual mobility and training scheme, and information services such as Eurolaser News and Eurolaser Bulletin Board Service. The Eurolaser Academy was set up to help industry through advanced postgraduate training in the fields of laser and materials processing technology. Originating from an initiative by the Eurolaser Government Coordination Committee in 1991, and supported by the COMETT Programme of the Commission of the European Union, the Eurolaser Academy provides an intensive, modular, fourweek course in industrial laser technology designed to augment the skills
of qualified engineers and physicists through a balanced combination of lectures, practicals and tutorial work. Those who benefit immediately from the training are predominantly graduates in the fields of mechanical production and electrical engineering, physicists or those in related numerate disciplines, and existing engineers already qualified by the ECCW. The ultimate beneficiary will be European industry, which should benefit in the medium to long term through improved productivity and profitability. Eurolaser Academy, c/o Igor Arbanas, Mostgasse 3, A1040 Vienna, Austria. Fax: +43 1 586 1780 0 Eurolaser Academy (UK), cfo Roger Crafer, Abington Consultants, 78 High Street, Abington, Cambridge CBl 6AE, UK. Fax: +44 1223 891 576 0
Centre for manufacturing cylindrical lenses In response to strong and growing OEM demands, Melles Griot has announced a major expansion of its cylinder lens manufacturing capabilities with the opening of a new Cylinder Lens Manufacturing Centre in the USA. The new facility manufactures both positive and negative cylindrical elements, from 3 mm to 510 mm long, to precision tolerances and tight cosmetic specifications. The Centre is also able to fabricate more unusual optics, such as cylindrical rods, wedged cylinders and cylinders made from unusual optical glasses. The company now has over 35 specialized machines for cylinder lens fabrication, with a capacity exceeding 10,000 lens elements per month. Melles Griot also offers a complete range of cylinder coating capabilities, including multilayer, anti-reflective and reflective coatings. Melles Griot Ltd, Brookmount Court, Kirkwood Road, Cambridge CB4 2QH, UK. Fax: +44 (0)1223 425310
0 Optics
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& Laser Technology Vol 27 No 3 1995
News update Laser power
and position
Non-invasive in-line monitoring of high-power CO2 lasers can be carried out with the BM 10.6 Beam Monitor, developed by Precision-Optical Engineering. Claimed to be the first system to offer a safety interlock, the unit can also be used in system alignment, giving a maximum output when the beam is correctly aligned. In the past, in-line monitoring of high-power laser beams, especially for safety procedures, has proved difficult, Methods using components such as beam-splitters have been used, but these can be unreliable, as the components’ characteristics could change as a result of the high intensity beam being used. For safety monitoring of beams, often only passive systems are used, effectively relying on an operator spotting the results of a stray beamthat is, smoke or burning-before the laser could be switched off. The recently launched beam monitor, however, is an active component and can act as an in-line, intrinsic power and position safety monitor. In effect, the monitor samples a very small fraction of the beam (- O.OS%), through which changes of 0.5% of the incident power can be detected. Thus, if there is a fluctuation in power-for example, if the beam is moved out of alignment or, for some reason, it is being interrupted-the system will monitor
safety
monitor
works
in-line Fold
Used as a final fold monitor can provide system
mirror in a beam delivery line, Precision-Optical Engineering’s beam an indication of beam power stability at the output of a processing
this and switch off the laser. The main component is a specially developed diamond machined mirror. This has been machined by PrecisionOptical Engineering to diffract a specific proportion of the beam at a specific angle. In the CO;! monitor, the 10.6 urn beam has about 0.01% diffracted into a thermopile detector. Changes of 0.5% can be detected through this method ensuring high
sensitivity and a 40 ms response time. Designed and manufactured by Precision-Optical Engineering, the mirror is made from OFHC copper and is water cooled to allow a wide range of beams up to, for example, 10 kW. Beams up to 45 mm diameter can be accommodated, making the unit suitable for a wide range of applications including: safety interlock beam power stability 0 system alignment l beam wander alarm l backscatter monitor 0 process monitoring l l
Having no moving parts, the beam monitor is a low maintenance unit, which can be used with most laser/ electronic control systems for laser processing machines. It interfaces easily to most control systems. The heart of Precision-Optical Engineering’s CO 2 laser beam monitor is the sampling mirror, which has been diamond machined to produce first-order diffraction thermopile detector
Optics & Laser Technology Vol 27 No 3 1995
copper into a
Precision-Optical Engineering Ltd, 42 Wilbury Way, Hitchin, Hertfordshire SG4 OTP, UK. Fax: +44 (011462 440329 0
V
News update Market
forecasts
for industrial
Spurred on by new applications, improving technologies and demand from new regions, worldwide sales of industrial and scientific laser systems will grow from $1.4 billion in 1993 to $2.25 billion in the year 2000, according to a study recently released by Frost & Sullivan. The report, Industrial and Scientific Lasers: Industrial Sales Lead Resurgence in Growth, states that, in 1993, CO2 lasers accounted for 45% of market revenues, solid-state lasers 26%, diode lasers 16% and ion lasers 6%. Over 90% of this combined market is accounted for by industrial applications, which are growing more rapidly than scientific ones. However, lasers have also established themselves as prime equipment for many scientific applications-most notably spectroscopy. New capabilities with faster repetition rates and wider wavelength range are continuing to aid the spread of lasers in the scientific community. The report states that there will be an increasing shift towards selling lasers in new areas of the world, including China, the former Soviet Union and eastern Europe, and numerous parts of the Third World. With the Japanese laser market starting to mature in several segments, Total industrial and scientific laser systems market: unit shipment and revenue forecasts (world) 1990-2000 according to Frost & Sullivan
Year
Units (Million)
1990 42.5 1991 46.2 1992 50.4 1993 55.0 1994 60.4 1995 66.8 1996 73.0 1997 80.1 1998 88.1 1999 97.4 2000 107.9 Compound annual 2000) = 7.0%
Revenues ($ billion)
Revenue growth rate (%)
1.31 1.33 1.34 1.41 1.51 1.62 1.73 1.85 1.98 2.11
1.7 0.3 5.3 7.3 7.3 6.9 6.8 6.9 6.8
2.26
6.7
growth rate (1993-
lasers
growth in China and Korea may increasingly lead Pacific Rim growth. Diode lasers have increased their penetration, taking over the barcode scanning market and establishing themselves in optical storage and printing applications. Tunable solidstate lasers, Frost & Sullivan believe, have established themselves as a force in the scientific market, with their ease of operation and performance making them preferable to more traditional tunable lasers. Advances in new laser varieties have meant declines for other segwith HeNe lasers losing ments, markets with the proliferation of diode lasers, and dye lasers losing heavily in the scientific market with the advance of tunable solid-state lasers. In materials processing applications, competition between CO2 and solid-state laser systems has increased in the last few years as it has between Nd : YAG and excimer lasers. The global market, the report states, has seen unprecedented price competition and aggressive marketing both between manufacturers of the same media and between different media. Competition will intensify, increasingly pressing profit margins. While the market will continue to grow, Frost & Sullivan believe, it remains strongly susceptible to cyclical recessions. Consolidation has progressed in response to globalization and the early 1990s’ market slowdown. Those lasers with the largest sales will see the most gains in new capabilities and performance as stronger sales lead vendors to put more resources into R&D and therefore increased functionality. Advances through the remainder of the decade, the report states, will include the development of new laser media-particularly in the tunable solid-state and diode laser markets; development of higher-power lasers generally, especially in the industrial CO*, diode, excimer and solid-state
laser market; development of lasers with higher repetition rates, particularly in solid-state markets, and development of direct-output blue solid-state lasers and blue/green diode lasers with outputs under 543 nm. The report is priced at $1895. Frost & Sullivan, 2525 CharLeston Road, Mountain View, California 94043, USA. Fax: +1 415 961 5042 Frost & Sullivan, Sullivan House, 4 Grosvenor Gardens, London SW1 W ODH, UK. Fax: i-44 (171) 730 3343
0
Fibre-optic spacecraft monitor to be developed Mission controllers of orbiting spacecraft, in the past, have had to rely on binary microswitches-which were often unreliable-to tell them whether on-board deployment mechanisms had operated or not. Now, the European Space Agency (ESA) has asked Sira to solve this problem by designing a low-cost, totally passive, but highly flexible fibre-optic spacecraft monitoring system. ESTEC, ESA’s technical research arm, has awarded Sira a feasibility contract to investigate how such a system could be designed with minimal installation and power requirements, yet be capable of providing a clear picture of whether six or more critical deployment or scanning mechanisms have been accurately deployed. According to Sira’s Dr Mike Cutter, the task will involve an assessment of the feasibility of optically multiplexing six or more optical-fibre transmitted images to one or more smart sensors with on-chip processing capability. He said, ‘The beauty of a passive fibre-optic system is that it can be fitted after the spacecraft has been assembled with minimal concern for interface issues such as electromagnetic interference.’ There will be a single central image-acquisition and processing unit with the ability to select which sensor Optics
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& Laser Technology Vol 27 No 3 1995
News update to view, what time resolution to use and the most appropriate data rate. This unit will be the only powered part of the system and will be capable of storing data and transmitting it to the ground. Smart sensors with on-chip processing capability will be required to carry out some data reduction. Although each sensor will have a fairly low resolution of 256 x 256
pixels, this still represents a large amount of data, even at a low data rate. The sensors will have to be capable of observing deployment from close to the spacecraft out to a distance of about 6 m and provide a reasonable focused image over the range. Sira Ltd, South Hill, Chislehurst, Kent BR7 .5EH, UK. Fax: i44 (0) 181-467 6515 0
Lenses for image processing Designed for use in image processing, a range of high-quality lenses has been introduced by Rodenstock. The Magnagon lenses are suitable for use in image processing applications, in conjunction with electronic image scanners, where high demands are made on the optical imaging quality. The first lens to be introduced in this range was the Magnagon CCD 4.0/75 mm, which is claimed to give exceptional quality over a wide scale range.
The Magnagon
range
applications
The principal lens are
characteristics
of this
0 very low flare free of vignetting for the entire magnification scale l low longitudinal chromatic aberration a high-quality, independent of the magnification used l
Opt&he Precision strasse 43, many. Fax:
Werke G Rodenstock, Optics Division, IsarD-80469 Munich, Ger0 f49 89 7202 141
of CCD lenses is available from Rodenstock
lnterferometric
research in ophthalmology --
Research work in the Institute of Physics at the Technical University of Wroclaw, Poland, is currently dealing with the application of interferometric methods in ophthalmology. Dr Henryk Kasprzak and his team are co-operating with an Eye Clinic to develop some new measurement
techniques that can be applied in ophthalmic practice. One study, for example, has performed in vivo analysis of the dynamic changes of the cornea1 contour to a submicrometre accuracy by using interferometric methods. In this work, a Twyman-Green interferometer was used for the
analysis of the wavefront reflected from the human cornea in vivo. The analysed wavefront interfered with the reference one and produced a rapidly moving fringe pattern related to the motion of the eyelid. The rapidly moving fringes were recorded on videotape and sequences of frames from the videotape, delayed by 40 ms, were stored and processed. The fringe patterns were numerically analysed and three-dimensional plots of the cornea1 contour were determined. Numerical subtraction of every two neighbouring three-dimensional plots created a sequence of new contour representing maps, changes in the cornea1 geometry within each 40 ms time period. The three-dimensional plots of the differences of cornea1 contours obtained from the neighbouring frames of the videotape show that the cornea does not behave as a rigid body in the fast motion of the eyelid but deforms and varies its topography in time. Another experiment studied, using in vivo interferometric examination, the human tear film and also observed the kinetics of different forms of the tear film’s irregularities. In this study, a human eye was inserted in one arm of the TwymanGreen interferometer, and a HeNe laser was used as the light source. The interference of the wavefront reflected from the cornea1 tear film, with the reference wavefront, produced a rapidly moving fringe pattern, disturbed by irregularities in the tear film. The observed image of the fringe pattern was recorded on a video recorder with a CCD camera. The selected frames from the videotape were stored and processed in a PC computer. The rapidly moving fringe pattern showed an irregular form shortly after an eye blink, after which the irregularity of the tear film reduces after about 3-5 s. After that time, the cornea1 surface becomes more and more smooth. However, when the eye remains open, an increase in fringe irregularity can be seen. After about 30 s from the last blink, the fringes are extre-
Optics & Vol 27
Laser Technology No 3 1995
vii
News update mely irregular, due to the drying of the tear layer and the roughness of the cornea1 surface. It is claimed that the types of observed irregularities of the tear film can be divided into four groups. Dr Henryk Kasprzak, Institute of Physics, Technical University of Wroclaw, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland. Fax: (0048 71) 22 96 96 0
System for high-precision laser machining Specifically designed to machine tiny objects with high precision, the Laserlith system has been developed by Advanced Recording Technologies (ART). With the laser-based micromachining station, rings and gears less than 0.002 inches (N 0.05 mm) in diameter can be made from a variety of materials. In addition letters only 0.006 inches (N 0.15 mm) high can be clearly scrolled out. According to the company, the high precision is attained through the use of a highly stable cultured granite housing, coupled to laser controlled interferometer stages. In addition, to attain high reliability, the system uses diode-pumped YAG lasers rather than the more conventional krypton arc pumped systems. The system has an accuracy of up to 0.25 pm, a speed up to 8 inches per second (-203 mm ssl ) and kerf widths to 0.5 l.rrn. Applications for the system are thought to include the precision micromachining of ceramics, metals and glasses, such as ferrite, aluminium oxide, calcium titanate, stainless steel, aluminium titanate carbide and silicon carbide. Many types of lasers can be installed in the system, including diode pumped YAG and YLF, Qswitched, mode locked, doubled, nitrogen, pulsed or tripled, C02, continuous lasers. Advanced Recording Technologies, 1310 Industrial Avenue, Escondido, C$it;;ja 92029, USA. Fax: +1619 0
Laser micromachining A micromachining system has been developed by Cambridge Consultants Ltd (CCL) for the Defence Research Agency (DRA). The system was delivered to an exacting time scale and specification and is being used for the ultraviolet optically assisted etch of ceramic infrared electro-optic chips, such as those used in high resolution, room temperature, infrared imaging devices. DRA’s original system used one laser beam to cut microscopic grooves, which form the individual detector elements that together comprise the image sensing array. This proved to be time consuming and restricted to smaller, lower resolution arrays. CCL developed a system that simultaneously generated five focused laser beams so that five grooves were machined in parallel. This process enabled larger arrays to be manufactured at five times the speed. The specification was exacting, but CCL’s specialist skills in optical engineering ensured that the lasers conformed to an ultra-precise geometry and were also very closely matched in power and spot-size to enable each groove to be machined at
Arrays can be manufactured speed laser micromachinery
system has high speed the same rate. By drawing on skills in system design and optical engineering, CCL was able to meet all the key performance demands. The system uses an array of beam-splitting and conditioning elements to generate an angular array of beams that are focused by a custom ultraviolet objective. A novel use of optical retarders enables loss-free power balancing and contributes to a very high overall efficiency in excess of 75%, allowing a 3 W laser to be used in future systems and achieving considerable savings. Through a combination of precision machining, interferometric prealignment and the subtle use of ‘optical-levers’, the system is simultaneously robust and stable whilst being very simple to bring into precise alignment. In consequence, although no testing was possible until integration with the high-power laser at DRA, successful cutting was achieved on the first attempt. Cambridge Consultants Ltd, Science Park, Milton Road, Cambridge CB4 4DW, UK. Fax: +44 (O)I223 423373
at five times the speed of original equipment devetoped by CCL
equipment
Optics VIII
with the high-
& Laser Technology Vol 27 No 3 1995
Fibre-optic
system finds use underground
A Distributed Temperature Sensing (DTS) system from York Sensors is being used to monitor Underground Coal Gasification (UCG) in a European trial being carried out by a partnership of Spanish, Belgian and British companies with European Community support. The in situ conversion of coal into gas will be attempted by Underground Gasification Europe AEIE (UGE) in a 600 m deep seam of black lignite in the province of Teruel in the north-east of Spain. In the project, three types of well are drilled into the coal seam. Injection wells are used to ignite the coal and to carry oxygen to the seam; a production well recovers the gas and monitoring wells assess the development of the gasifier. In practice, the process is more complex and, in reality, operates like an underground chemical reactor at high temperature and high pressure. With further refinement, some researchers believe that within 20-30 years UCG technology could be used to recover gasified coal from closed pits. York’s distributed temperature sensing system is coupled to a specially designed fibre-optic cable to withstand the harsh environment and will monitor the reactions continuously. It will provide distributed measurements of temperature each metre down the length of the wells. From these measurements UGE can monitor the temperatures of the reaction zones, which can reach 1100°C. Traditional temperature measurement devices will also be used but cannot compete with the amount of data that can be generated from a singe sensor cable. Cavity growth-that is, how much of the coal seam is being convertedwill also be monitored using the DTS system by measuring how much of the sensor is destroyed as the combustion zone progresses through the seam. York Sensors’ DTS system has already been successfully tested by companies, including British Coal, Optics & Laser Technology Vol 27 No 3 1995
National Grid and Copenhagen Energy, to provide a cost efficient means of monitoring reactions through temperatures. The DTS System consists of the following. l
l
l
An instrument containing an OTDR (Optical Time Domain Reflectometer), coupled to a microprocessor controlling signal processing in real time. One to six sensors each up to 10 km long, consisting of loops of standard telecommunications-grade multimode optical fibre. DTS Manager, a Windows application running on a 386 or 486 PC.
A typical installation of 4 km sensor cable can provide up to 16000 points of temperature versus
Stepper
York UGE tion. head box
used by gasijica1 welljunction
distance information to a resolution better than 1°C. These data can be updated every few seconds or several minutes apart. The spatial resolution is 1 m. York Sensors Ltd, York House, School Lane, Chandlers Ford, Eastleigh, Hampshire SO53 4DG, UK. Fax: 01703 267234 0
lens manufacturing
Carl Zeiss is nearing completion of a three-year, $37-million expansion programme that will increase its manufacturing capacity in stepper lenses to keep pace with the highvolume demand of its leading customer for microlithography optics, ASM Lithography (ASML). The expansion, scheduled to be completed by the second quarter of 1995, will enable Carl Zeiss to increase its stepper lens production to more than 200 units per year, matching ASML’s annual capacity in stepper systems. The strategic partnership between Carl Zeiss and ASML began in 1989, when the companies established common policies involving product strategy, technology development and quality assurance. Carl Zeiss’ experience in developing microlithography systems dates back to 1972 with optics for 1:l photorepeaters. ‘Today, our microlithography lens division reinvests more than 30% of its revenues to fund continuing research and development work and to meet the increasing market demands for stepper lenses’, said Dr Dieter
Sensors’ DTS system is being to monitor underground coal Shown here is Injection Well and the optical fibre cables’
improved
Kurz, director of optical lithography components with Carl Zeiss. ‘This latest expansion continues our strong commitment to advancing microlithography optics technology.’ ASM Lithography, 2315 West Fairmount Drive, Tempe, Arizona 85282, USA. Fax: +1 602 0793 0
Radiometric and photometric measurements described Light measurement instrumentation, applications and the basic concepts of radiometry and photometry are described in a catalogue available from International Light. It describes thousands of contigurations and combinations of systems for performing radiometric and photometric measurements. Developed for those involved with light measurements-regardless of their level of expertise-this expanded catalogue includes applications, tutorials, spectral graphs and spatial information. International Light Inc, 17 Graf Road, Newburyport, Massachusetts 01950, USA. Fax: fl 508 462 0759
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News update Improved
assembly
for rectilinear
A special assembly process has been developed by Rodenstock for rectilinear lenses. Rectilinear lenses are used in scanners where, owing to the reduced size of the lens, more compact system designs are possible. In addition, owing to the minimized dimensions, the production of the lenses allows a much higher loading per polishing tool than in round lens production. Thus, valuable polishing time can be saved. While, in traditional lens construction, the lens elements and their mounts require surfaces to determine the position that is to be worked, with very tight tolerances; in Rodenstock’s system, the function of these surfaces can be dispensed with.
lenses
The lenses-whose edges can be of any shape-are positioned exactly using an air-cushioned rotating stroke spindle in conjunction with a positional sensor for the optically effective surfaces outside the lens housing. Only then are the aligned lenses moved to the final position in the mount housing in a program-controlled process. The lenses are fixed in position with a tolerance of 0.001 m, using a patented cementing process. The mount housing has only a holding function and, like the edging surfaces of the lens, can be produced using only very rough tolerances. With rectilinear lens technology, the precision stands and falls with the special equipment used, the assem-
bly, and the assembly process. This precision is copied into the lens element by element. It therefore does not need to be generated by extremely tight production tolerances. A further advantage of rectilinear lens technology when used in scanners, is the miniaturizing of the scanning lens. As the deflection element of the output scanner can be moved closer to the lens, a further degree of freedom is obtained for correction (distance of pupil to lens). With a short pupil distance, the lens diameter is also automatically reduced and, in a number of cases, the lens can have a smaller design than a lens with a round shape. Optische Werke G Rodenstock, Precision Optics Division, Isarstrasse 43, D-80469 Munich, Germany. Fax: +49 89 7202 141 0
Improved manufacturing means fewer trace elements in quartz glass Quartz glass with fewer trace elements has been developed by Heraeus. The company’s quartz glass manufacturing technology eliminates most heavy metals and other impurities from its raw quartz materials. Compared with standard semiconductor quartz glass grades, the recently developed HSQ 351 (standard) and HSQ 751 (improved quality) significantly reduce the migration of trace elements (like alkali and heavy meals) to the wafers. Thus, wafers are protected against minority carrier lifetime degradation, which is a serious indicator for upcoming yield problems. Application studies about the interaction of quartz glass and silicon wafers show about 50 to 100 times less heavy metals in the bulk of the wafers processed with HSQ 351 or HSQ 751. Additionally, the quality of the surfaces, with respect to saucer pits and oxidation stack faults, was substantially higher. Rodenstock’s assembly process for rectilinear lenses. At the bottom of the figure can be seen the rotating stroke spindle (which was produced in-house due to the high demands on its precision) with the rectilinear lens in place. At the top, the jig for the mechanical housing can be seen. Once the lens has been aligned on the spindle, it is moved into the mount from below
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Heraeus Quarzglas GmbH, SemiDivision, D-63801 conductor Kleinostheim, Germany. Fax: +49 6027 507 278 0 Optics & Laser Technology Vol 27 No 3 1995
Is your safety equipment up to the European Union CE mark? It will be illegal, from 1 July this year, for manufacturers to sell new eye and face protective equipment that does not carry the European Union CE mark. In addition, the same legislation applies to other items of personal protective equipment including ear defenders, safety helmets, respirators etc. However, the CE mark in itself is not a European standard it is an indication that the product meets the requirements of the Personal Protective Equipment (PPE) Directive which is now part of UK law. A European standard, EN 166, which will bring about a uniform technical specification throughout the Union, is expected to be published later this year. Convenor of the ELI’s technical committee working group on industrial eye protection, David Yelland, said ‘The CE mark is an important stage in assisting free trade between member states. Products carrying the mark will be recognized in all countries. but we still have to finalize EN 166. Until we do so, manufacturers can obtain their CE mark by demonstrating product conformance with existing national standards or the draft European standard, prEN 166.’ ‘Progress towards agreeing a technical standard across the European Union has been painfully slow.’ David said, ‘With countries believing their own requirements to be satisfactory. This has meant that international trading has been hampered by the need to have approval for each country.’ ‘Now we are making headway, and the introduction of the CE mark is significant. Eventually, when EN 166 is approved and published, all eye and face protective equipment will have to meet its standards, which I see as an amalgam between the UK’s BS 2092 and the German DIN requirements.’ ‘For British producers this will not be much more stringent than BS 2092, but it will contain additional optical requirements and introduce new marking symbols for impact resistance, molten metal protection etc.’ Although the regulations relating to the CE mark finally take effect this summer, unmarked products already in the supply line before 1 July can still be issued and used for their normal, serviceable life. From that date some items will carry both the CE and BS markings. David Yelland said, ‘This is perfectly legal as the new legislation does not specify the technical standard to which the CE certification is obtained.’ Manufacturers believe they have won a victory over bureaucrats in Brussels who originally also wanted the year of testing to be included as an integral part of the CE mark.
Optm
David, who is also Group Technical Director of Pulsafe Safety Products, said, ‘Annual changes would require expensive changes in marking plates and now it seems certain the suggestion will be dropped.’ He added, ‘The form of the CE mark itself depends on the product category and will be changed again after January 1997 in order to harmonize PPE products with others.’ According to David, ‘The best advice for purchasers and end users concerned with category two and three products over the next two years is to look for the CE mark and the four-digit number of the notifying body.’ If the latter is not there, questions should be asked, as the four-digit number is optional on category two products but mandatory on category three items.’ Effectively, PPE category one products are of simple design and would involve only minor, reversible user harm should they fail. Category two products are of intermediate design where failure could cause serious permanent injury, while category three products are of complex design where failure could cause fatality. Under the CE regulations, category one products can be self-certificated, while type testing by a Notified Body is required for category two. For category three products to be approved there has to be type testing by a Notified Body plus ongoing certification either through annual repeat testing or by means of BS5750jISO 9000 accreditation. David Yelland warned that some manufacturers are already offering products marked EN 166. ‘This cannot be correct. There is no such thing as EN 166, and the products should be properly marked prEN 166 which indicates that they have met the requirements of the draft European standard.’ ‘But the question then is, “which draft?“, because there have been three versions since CE certification began, and the latest of these has different marking symbols compared with the first two.’ David explianed his own compnay’s position, ‘It is because the goalposts were shifting so frequently that at Pulsafe we decided to obtain our CE marking approval on the basis of BS 2092.’ ‘That decision could be seen as being anti-European or retrogressive,’ he said, ‘But the pitfalls of using a nonproven draft standard were too great to ignore. If products were approved to prEN 166 then each time the draft was updated and/or the marking symbols changed the customers would need to be re-educated on their meanings.’ ‘With such changes in markings there could be apparently identical products on the market with marking symbols having fundamentally different meanings.’ He added, ‘Approval to draft standards is a potent recipe for total confusion.’ The eye and face protective sector is not the only part of the PPE industry where EN standards have not yet been finalized. Manufacturers of air-fed respirators,
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News certain types of gloves and ear defenders are still awaiting announcements, but they will all have to use the CE mark from 1 July. So, does the arrival of the CE mark in the market place mean the-end of the UK Kitemark? David said, ‘The Kitemark will have just as much relevance as it did before the introduction of the CE mark. They are two totally different entities. One cannot replace the other, but they can co-exist.’ He contined, ‘The Kitemark is a quality indicator. The CE mark is a legal rubber stamp. The CE mark is not a substitute for the Kitemark, and was never intended to be so.’ He added, ‘The Kitemark is a much more rigorous scheme than the CE mark. The CE mark, once awarded, never has to be independently verified thereafter, whereas the Kitemark is subject to continuous scrutiny.’ ‘I suggest that customers look for both marks the CE because it is a legal requirements and the kite because it gives independent third party assurance of continuing product conformity.’ ‘Apart from the obvious advantages, this could carry weight in the event of product liability claims.’ The Kitemark is quite expensive to maintain and there may be some manufacturers who take the opportunity to drop it during the confusion surrounding the introduction of the CE mark.
Update
‘The fate of the Kitemark is in the hands of the purchaser and end user. It will continue as long as it is in demand and providing no one is fooled into believing that it has been replaced by the CE mark.’ ‘Manufacturers who have adopted the perilous route of draft European standards could find the Kitemark denied them as BSI will not offer Kitemark schemes to draft standards.’ UK regulations arising from the European PPE product and workplace directives are enforced by trading standards officers and HSE (Health and Safety Executives) factory inspectors respectively. Said David Yelland, ‘The most important obligation falling on employers under the PPE at Work Regulations is the responsibility for selecting suitable personal protective equipment for staff.’ ‘That responsibility cannot be passed off to the manufacturer whose duty is to provide information concerning product performance.’ ‘The establishment of common European product standards and workplace regulations has been a long drawn out process and has led to a great deal of confusion and misunderstanding. But now the task is almost complete and it must be hoped that the intended benefits to worker safety and pan-European trading practices will begin to be realized in the months ahead.’
Research institutions, universities and companies with news and laboratory reports they wish to have included in the news update sections of Optics & Laser Technology should contact the managing editor at the address given below. Details of current projects and research work which would interest the international readership of Optics & Laser Technology are welcomed.
Nick Butler, Managing Editor Elsevier Advanced Technology Optics & Laser Technology
PO Box 150, Kidlington Oxford OX5 1AS, UK Tel: + 44 (0)1865 843677 Fax: + 44 (0)1865 843971
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