Optoelectronics

Optoelectronics by Dr J. Schanda Report on sessions dealing with optoelectronics at the Xth IMEKO Congress Two sessions were devoted to optoelectronics at the Xth IMEKO Congress in Prague 22-26 April 1985. During the Session No S11, 'Electro-optical Measuring Methods', eight papers were read dealing with the application of optoelectronics in measurement techniques. Two papers discussed basic photometric and radiometric questions: Jedlicka, Zatkovic and Jediny addressed the question of low light level photometry, compared the black-body and the radiometric detector standard methods, and showed the amount of error that can occur if instruments designed for photopic measurements are used in the mesopic or scotopic range. They designed a low level luminance standard that can be used to calibrate photometric instruments at low light levels. By adjustment, the luminance of the exit window can be changed by many orders of magnitude. Eppeldauer discussed the problem of measuring low light intensities by using photovoltaic cells, and described a system that enables the measurement of 10 -15 A photocurrents that can also be used to determine the external quantum efficiency of the detector so that it can be used as an absolute radiation standard. Three papers dealt with the quality control of cold rolled steel sheets. Two of them tackled the question of surface roughness: Asano and co-workers used two lasers to irradiate the surface and measured the reflexion indicatrix in two restricted regions. Uesugi and co-workers found that the standard deviation of the video signal obtained with an ITV camera through a low magnification microscope under diffuse illumination is proportional to the rms value of surface roughness. They were mainly interested in the line-shaped surface defects. The paper by Tarao and co-workers described a colorimeter for the quality control of coloured galvanised sheets based on a 31-wavelength channel spectrophotometer and microprocessor controlled evaluating system enabling several measurements per second with a reproducibility of 0.1-0.2~o AE. The paper by Issa and Maamoun dealt with the quality control of plastic materials, measuring the scat-

Measurement Vol 3 No 2, April-June 1985

tered radiation of the modulation of linearly polarised light: the so-called photoelastic isodyne fringes are well suited to identify the type of the polymer material and can be used also for the quality control of the transparent plastic material. Driescher in his paper on a method of optoelectronic switching point adjustment demonstrated a procedure permitting a stepless displacement of a switching point without mechanical adjustment by means of a duplex beam gate. A very topical question relating to 'robot-eyes' was discussed by Mfihlenfeld: optical edge detection and pattern recognition. Instead of taking a full picture of the sample and digital processing of this picture, the device scans only the contour of the target, resulting in a selection of the most significant information. This reduces computer workload to the capacity of a minicomputer (PDP 11/23); the adaptation to the expected information improves the system detectivity. Another session on optoelectronics was a round table discussion of the IMEKO TC-2: Photon Detectors, where a short information on the Symposium of the Committee held in 1984 in Weimar was presented, followed by discussions centred around questions of detectors with spatial resolution (CCD cameras versus vidicon type detectors) and detectors with high bandwidth (PIN and avalanche diodes versus phototubes with special time dissecting capabilities). Problems of absolute photometry and radiometry, as well as application of optical detectors in mechanical, biological and medical instrumentation, were also discussed. These questions will stand on the working programme of the next IMEKO Photon Detectors Symposium, scheduled for May 1986 in Varna, Bulgaria. Papers dealing with questions related to photoelectric sensors and instruments were discussed also in a number of other sessions, grouped around the material to be tested or the quantity to be investigated. Reports on these papers will be published eventually in other reports of the Congress.

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