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Volume B: Optical characterization methods and techniques
ARTICLE IN PRESS
Optics and Lasers in Engineering 45 (2007) 349–350
Editorial
Volume B: Optical characterization methods and techniques Optical characterization is increasingly extending to materials, components and devices, both at the micro and macro scale. Numerical simulation has also made enormous progress, especially thanks to the continuous upgrade of computer power. This makes possible detailed design of complex optical systems as well as modelling of experiments, in order to improve theoretical models and predict the behaviour of engineered optical materials. The latter subject is of utmost importance during microstructuring of linear and nonlinear materials in view of specific optical applications. Such micro-components are essential for a wide range of applications, spanning from telecom to the development of optical microsensors or microresonators for coherent radiation generation. It is interesting noticing that the development of microcomponents, traditionally made using semiconductors, especially silicon, is more and more moving towards not only optical fibers (e.g. microstructured fibers, or fiber Bragg gratings) but also to nonlinear optical materials, like LiNbO3, that can have an unusually rich variety of interactions with light and are transparent in wide spectral ranges, typically from the mid-IR (3–5 mm wavelength) across the entire visible portion of the spectrum. Of course, size scaling of such engineered materials towards micro and nano dimensions is more demanding for optical characterization techniques as well as for light propagation modelling. Therefore, novel optical techniques are being developed, that are often combined with other instrumentation, like atomic force microscopes, X-ray scattering, electron beam microscopy, to achieve a thorough understanding of the processed materials at such small scales. In the present volume papers concerning different aspects of optical technologies are collected. A method for characterizing solar concentrators and their embedded optical components is reported in the work of P. Sansoni et al. in which experimental procedures are proposed and discussed to estimate the collection efficiency of the lens, as well as the energy distribution in the image plane. In the paper by P. Carcagnı` et al., a scanning system for multi-spectral imaging of paintings in the 380–800 nm spectral region is presented, specifically developed to
0143-8166/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlaseng.2006.03.001
overcome most of the problems related to traditional detection systems based on CCD or Vidicon cameras. Successful application to an ancient painting, covering an area of 1 m2 with 16 dots/mm2 spatial resolution and 10 nm spectral resolution, is demonstrated. Switching from the macro to the micro scale, the next work describes a scanning micro-interferometer, with a Mach-Zehnder configuration realized by using non-standard processes of planar technology on lithium niobate crystals. The performances of the integrated optical spectrometer were preliminarly tested in the spectral window ranging from 0.4 to 1.0 mm. In a further experiment, the performances of the microinterferometer were tested for trace gas detection by using a calibrated NO2 optical gas cell. One additional important issue of the characterization of optical crystals has been addressed in the paper by M. Bazzan et al. There, characterization of periodically poled lithium niobate structures with periods ranging between 2 and 10 mm is reported. The approach followed in the paper was to characterize either the domains distribution along the crystal by a profilometer and its non linear efficiency by means of second harmonic generation. By a numerical analysis, feasibility of backward second harmonic generation in the sample with the shortest domain period has also been verified. In the work by P. Galinetto et al., a micro-Raman analysis on lithium niobate (LN) substrates is reported. It was accomplished in order to study the compositional homogeneity of the crystals and to clear up the effects of etching and polishing processes on the surface of wafers and crystals. By means of Raman analysis, in combination with a confocal microscope, the possibility to determine the sample stoichiometry and the crystalline quality has been demonstrated. Finally, a paper is devoted to an interferometric characterization method to evaluate the measured strain by means of a Fibre Bragg Grating (FBG) sensor. Using a Digital Holographic technique, it is shown that in-plane strain can be measured and compared with the strain detected by an optical fiber attached on it. This is a general
ARTICLE IN PRESS 350
Editorial / Optics and Lasers in Engineering 45 (2007) 349–350
technique that allows to quantify if, in a specific FBG configuration, all the effective strain acting on the surface is transferred to the FBG sensor. We gratefully acknowledge the Editor in Chief Pramod K. Rastogi for making possible this special issue and Mrs. Carmen Addeo (CNR-INOA- Napoli) for taking care of the manuscripts.
Paolo De Natale Pietro Ferraro Istituto Nazionale di Ottica Applicata (INOA) del CNR, Via Campi Flegrei, 34, c/o Compr. ‘‘Olivetti’’, 80072 Pozzuoli (Na), Italy E-mail addresses: [email protected] (P. De Natale), [email protected] (P. Ferraro)
Optics and Lasers in Engineering 45 (2007) 349–350
Editorial
Volume B: Optical characterization methods and techniques Optical characterization is increasingly extending to materials, components and devices, both at the micro and macro scale. Numerical simulation has also made enormous progress, especially thanks to the continuous upgrade of computer power. This makes possible detailed design of complex optical systems as well as modelling of experiments, in order to improve theoretical models and predict the behaviour of engineered optical materials. The latter subject is of utmost importance during microstructuring of linear and nonlinear materials in view of specific optical applications. Such micro-components are essential for a wide range of applications, spanning from telecom to the development of optical microsensors or microresonators for coherent radiation generation. It is interesting noticing that the development of microcomponents, traditionally made using semiconductors, especially silicon, is more and more moving towards not only optical fibers (e.g. microstructured fibers, or fiber Bragg gratings) but also to nonlinear optical materials, like LiNbO3, that can have an unusually rich variety of interactions with light and are transparent in wide spectral ranges, typically from the mid-IR (3–5 mm wavelength) across the entire visible portion of the spectrum. Of course, size scaling of such engineered materials towards micro and nano dimensions is more demanding for optical characterization techniques as well as for light propagation modelling. Therefore, novel optical techniques are being developed, that are often combined with other instrumentation, like atomic force microscopes, X-ray scattering, electron beam microscopy, to achieve a thorough understanding of the processed materials at such small scales. In the present volume papers concerning different aspects of optical technologies are collected. A method for characterizing solar concentrators and their embedded optical components is reported in the work of P. Sansoni et al. in which experimental procedures are proposed and discussed to estimate the collection efficiency of the lens, as well as the energy distribution in the image plane. In the paper by P. Carcagnı` et al., a scanning system for multi-spectral imaging of paintings in the 380–800 nm spectral region is presented, specifically developed to
0143-8166/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlaseng.2006.03.001
overcome most of the problems related to traditional detection systems based on CCD or Vidicon cameras. Successful application to an ancient painting, covering an area of 1 m2 with 16 dots/mm2 spatial resolution and 10 nm spectral resolution, is demonstrated. Switching from the macro to the micro scale, the next work describes a scanning micro-interferometer, with a Mach-Zehnder configuration realized by using non-standard processes of planar technology on lithium niobate crystals. The performances of the integrated optical spectrometer were preliminarly tested in the spectral window ranging from 0.4 to 1.0 mm. In a further experiment, the performances of the microinterferometer were tested for trace gas detection by using a calibrated NO2 optical gas cell. One additional important issue of the characterization of optical crystals has been addressed in the paper by M. Bazzan et al. There, characterization of periodically poled lithium niobate structures with periods ranging between 2 and 10 mm is reported. The approach followed in the paper was to characterize either the domains distribution along the crystal by a profilometer and its non linear efficiency by means of second harmonic generation. By a numerical analysis, feasibility of backward second harmonic generation in the sample with the shortest domain period has also been verified. In the work by P. Galinetto et al., a micro-Raman analysis on lithium niobate (LN) substrates is reported. It was accomplished in order to study the compositional homogeneity of the crystals and to clear up the effects of etching and polishing processes on the surface of wafers and crystals. By means of Raman analysis, in combination with a confocal microscope, the possibility to determine the sample stoichiometry and the crystalline quality has been demonstrated. Finally, a paper is devoted to an interferometric characterization method to evaluate the measured strain by means of a Fibre Bragg Grating (FBG) sensor. Using a Digital Holographic technique, it is shown that in-plane strain can be measured and compared with the strain detected by an optical fiber attached on it. This is a general
ARTICLE IN PRESS 350
Editorial / Optics and Lasers in Engineering 45 (2007) 349–350
technique that allows to quantify if, in a specific FBG configuration, all the effective strain acting on the surface is transferred to the FBG sensor. We gratefully acknowledge the Editor in Chief Pramod K. Rastogi for making possible this special issue and Mrs. Carmen Addeo (CNR-INOA- Napoli) for taking care of the manuscripts.
Paolo De Natale Pietro Ferraro Istituto Nazionale di Ottica Applicata (INOA) del CNR, Via Campi Flegrei, 34, c/o Compr. ‘‘Olivetti’’, 80072 Pozzuoli (Na), Italy E-mail addresses: [email protected] (P. De Natale), [email protected] (P. Ferraro)