JEOS:RP - Journal of the European Optical Society Rapid publications
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Imaging of plankton specimens with the lightframe on-sight keyspecies investigation (LOKI) system
Get PDFZooplankton is a key element in aquatic food webs. Rapid mapping of abundance, combined with information on taxonomic and size composition is necessary to understand ecosystem dynamics. Classical sampling with towed plankton nets does not allow resolving fine scale distributions along hydrographic gradients (e.g. fronts and clines) although such structures determine community assemblages and trophic interactions. Furthermore, sample analysis is labor intensive and time consuming. To overcome these shortcomings, Lightframe On-sight Keyspecies Investigation (LOKI), a new imaging device, was developed for sensing spatial variability of plankton distribution on scales below the 1~m level. Here, we give a brief description of the LOKI system and demonstrate its potential for taxonomic identification using images of various zooplankton taxa collected in the south east Pacific
Application of the method of auxiliary sources to a defect-detection inverse problem of optical diffraction microscopy
Get PDFWe propose a method of numerical solution of a type of inverse scattering problem that arises in the optical characterisation/quality control of nanostructures. The underlying global, ill-posed, nonlinear optimisation problem is first localised by best-fit matching of library and measured diffraction efficiency patterns. The inverse problem is then solved using piecewise linear interpolation between the best far-field matches. Finally, the results are refined, on average, by solving an additional local optimisation problem formulated in terms of the Method of Auxiliary Sources. To illustrate the proposed method, we apply it in a concrete quantitative characterisation of a non-periodic, nano-scale grating defect, with numerically simulated measurements. It is shown that the presented procedure can solve the inverse problem with an accuracy usually thought to require rigorous electromagnetic theories
Investigations on a robust profile model for the reconstruction of 2D periodic absorber lines in scatterometry
Get PDFScatterometry as a non-imaging indirect optical method in wafer metrology is applicable to lithography masks designed for extreme ultraviolet (EUV) lithography , where light with wavelengths of about 13.5 nm is applied. The main goal is to reconstruct the critical dimensions (CD) of the mask, i.e., profile parameters such as line width, line height, and side-wall angle, from the measured diffracted light pattern and to estimate the associated uncertainties. The numerical simulation of the diffraction process for periodic 2D structures can be realized by the finite element solution of the two-dimensional Helmholtz equation. The inverse problem is expressed as a non-linear operator equation where the operator maps the sought mask parameters to the efficiencies of the diffracted plane wave modes. To solve this operator equation, the deviation of the measured efficiencies from the ones obtained computationally is minimized by a Gauss-Newton type iterative method. In the present paper, the admissibility of rectangular profile models for the evaluations of CD uniformity is studied. More precisely, several sets of typical measurement data are simulated for trapezoidal shaped EUV masks with different mask signatures characterized by various line widths, heights and side-wall angles slightly smaller than 90 degree. Using these sets, but assuming rectangular structures as the basic profiles of the numerical reconstruction algorithm, approximate line height and width parameters are determined as the critical dimensions of the mask. Finally, the model error due to the simplified shapes is analyzed by checking the deviations of the reconstructed parameters from their nominal values
On the history of the Secchi disc
Get PDFThe first records on regular, tabulated, measurements of transparency of natural waters are those by the German naturalist Adelbert von Chamisso during the Russian ‘Rurik’ Expedition 1815-1818 under the command of Otto von Kotzebue. A standardized method to determine the water clarity (transparency) was adopted at the end of the nineteenth century. This method (lowering a white painted disc into the water until it disappeared out of sight) was described by Pietro Angelo Secchi in Il Nuovo Cimento and was published in 1865. The Austrian scientist Josef Roman Lorenz von Liburnau, experimenting with submersible objects, like white discs, in the Gulf of Quarnero (Croatia) in the eighteen-fifties, well before Secchi started his investigations, questioned the naming of the white disc. However, the experiments performed by Secchi and Cialdi in 1864, on such an intensive scale, where never performed before. At the beginning of the twentieths century this method, water transparency observations by means of a 30 centimetres’ white disc, was named the Secchi-disc method
Electro-optically induced absorption in α-Si:H/α-SiCN waveguiding multistacks
Get PDFElectro optical absorption in hydrogenated amorphous silicon (α-Si:H) – amorphous silicon carbonitride (α-SiCxNy) multilayers have been studied in two different planar multistacks waveguides. The waveguides were realized by plasma enhanced chemical vapour deposition (PECVD), a technology compatible with the standard microelectronic processes. Light absorption is induced at λ = 1.55 μm through the application of an electric field which induces free carrier accumulation across the multiple insulator/semiconductor device structure. The experimental performances have been compared to those obtained through calculations using combined two-dimensional (2-D) optical and electrical simulations
Alteration of optical and morphological properties of polycarbonate illuminated by visible/IR laser beams
Get PDFIn this paper we investigate the effects of visible to near infrared (NIR) laser illumination on the optical transmission (OT) and morphological changes (MC) of thin, curved surfaces of polycarbonate (PC) as employed by industry. The second harmonic of Nd:YAG laser (532 nm) and two diode lasers (665 and 980 nm) were used as sources. We have shown that the morphological changes and optical transmission of the PC elements are influenced by visible to infrared coherent illumination. The morphological changes of the PC surfaces are determined using atomic force microscopy (AFM), demonstrating the appreciable changes caused by the shorter wavelengths (higher energy). When analyzing the OT spectra of PC thin films, a measurable decrease in the OT of the PC surfaces which were illuminated by 532, 665 and 980 nm, in particular 532 nm, for energy densities greater than 25 J/cm^2 can be seen
Valentin A. Fabrikant: negative absorption, his 1951 patent application for amplification of electromagnetic radiation (ultraviolet, visible, infrared and radio spectral regions) and his experiments
Get PDFThis paper is devoted to Moscow physicist Valentin A. Fabrikant who is known for his 1939 thesis with suggestion of experiments on light amplification directly proving the existence of negative absorption in gas discharge, his 1951 patent application (jointly with M.M. Vudynsky and F.A. Butaeva) for amplification of electromagnetic radiation (ultraviolet, visible, infrared and radio spectral regions), and his experimental attempts (jointly with F.A. Butaeva) to observe light amplification in gas discharge (paper submission of December 1957)
Terahertz analysis of an East Asian historical mural painting
Get PDFTerahertz (THz) spectroscopy and THz and imaging techniques are expected to have great potential for the non-invasive analysis of artworks. We have applied THz imaging to analyse the historic mural painting of a Lamaism temple by using a transportable time-domain THz imaging system; such an attempt is the first in the world. The reflection image revealed that there are two orange colours in the painting, although they appear the same to the naked eye. THz imaging can also estimate the depth of cracks. The colours were examined by X-ray fluorescence and Raman spectroscopy, and the results were found to be in good agreement. This work proved that THz imaging can contribute to the non-invasive analysis of cultural heritage
Wavefront compensation method using novel index in holographic data storage
Get PDFPhotopolymer media that uses holographic data storage generally causes volume shrinkage. This volume shrinkage distorts the recorded interference fringes. We propose an adaptive optics using novel index to compensate this distortion. The SNR value is improved from 2.1 dB to 3.4 dB in the worst part of a reproduced image and the peak intensity and the full width of the half maximum of an angle are improved by 6% and 10%, respectively. These results prove that adaptive optics using this novel index worked effectively
Polymer co-crystalline films for photonics
Get PDFRobust syndiotactic polystyrene (sPS) films exhibiting highly stable co-crystalline phases can be obtained with a large variety of low-molecular-mass chromophore guest molecules. In this report different aspects relative to the structure and the optical properties of these films are described. In particular, possible applications of these films as fluorescent materials, as optical memories (based on the co-crystallization of photoreactive guest molecules), as non-linear optical materials (with polar guests) and as chiro-optical memories (based on temporary co-crystals with chiral guest molecules) are presented