This PDF file contains the editorial “Editorial: The Anatomy of an Invitation” for OE Vol. 34 Issue 04

This PDF file contains the editorial “Guest Editorial: Optics in the Ukraine” for OE Vol. 34 Issue 04

A review of the authors' experimental studies of photoinduced effects in thin light-sensitive films since 1976 is presented. In the first part of the review, the results of the optical and electron microscopic study of the Weigert effect in thin silver halide films containing granular Ag are observed. It is shown that the Weigert effect in these systems is connected with chains consisting of spherical silver granules oriented by a polarized laser beam. The second part gives the results of experimental studies of spontaneous periodic structures induced in thin light-sensitive films by a single polarized beam on scattered waveguide modes. The third part concerns the study of spontaneous gratings induced by an off-normal incident laser beam and their self-organization.

Interference and polarization-interference methods for measuring amplitude and phase parameters of random optical fields are reviewed and their applications to random field identification and diagnostics of random phase objects are discussed. The use of the correlation dimension of chaos in an optical field as a diagnostic tool is considered. The interference principles employed in parallel processing of large data bulks are shown to increase considerably the processing speed of diagnostic devices. That a proper account of the contribution of the longitudinal field component in the formation of such wave dislocations enables one to gain an insight into the wavefront formation mechanism in the vicinity of a zero amplitudeis also demonstrated.

New concepts are developed to describe a wide area of nonlinear systems involving the phase relaxation peculiarities for the degenerate two-level system under the resonant optical excitation. Nonlinear susceptibility of the two-level system becomes anisotropic, and self-induced changes of polarization (SICP) are developed to the large (gigantic) magnitudes. The nonlinearities of two different natures are considered: the saturation of absorption and the resonant optical reorientation of anisotropic defects. For these particular cases, the SICP effects manifest themselves at a field much lower than that in traditional nonlinear optics. The larger magnitudes of the effects offer good possibilities for the development of optical devices based on the new physical principles. Various applications of SlOP effects are demonstrated, including the spectroscopic investigations of impure cubic crystals, optical diagnostics, optical storage, information processing, and the development of new optical devices.

Measurements are presented for the photorefractive effect in CdTe using 10-ns pulses at a wavelength of 1.06 μm. Different self-action effects that accompany two-beam coupling are discussed.

Transverse optical bistability investigation review is presented. Aberration theory of the transverse optical bistability with counter-propagating light beam interaction is developed. The effect of aberration phenomena on switching thresholds is described and theoretical results are compared with experimental observations in α-SiC(6H) crystal.

The ability of rotated gyros to self-correct their errors is investigated. The specific design scheme of the device for three-axes orientation measurement enables using the self-correcting properties of rotation with maximum benefit. A mathematical model of the device using laser gyros is developed, on the basis of which computer simulation results are obtained. The proposed design scheme of the device due to its low sensitivity to gyro errors, including scale factor instability, is recommended for the use in strapdown navigation/orientation systems that employ not only a small-sized laser but also fiber optic or integrated-optic gyros.

The construction of two novel double-beam polarizational devices for the realization of the combined ellipsometric parameter method for solids and for liquids is described. As an example, the results of measurements based on this method for nonoxidic and oxidic surfaces of copper are presented.

Energetic, statistical, and temporal characteristics of a picosecond KGW:Nd laser based on the Sagnac interferometer are studied. All experiments are provided in comparison with the traditional linear cavity. The effect of stimulated Raman scattering suppression in such a specific cavity was found. Stimulated Raman scattering in KGW dumped all output parameters in the laser with a linear cavity. A new cavity scheme can solve such problems and provide for good output handling. It is shown that output pulse duration is larger in the proposed scheme compared with a linear cavity but other characteristics are much better.

A generalized analysis of the results of several studies of the properties, structure, and the optical-geometric parameter peculiarities of the influence of high temperatures on light-scattering objects of various physical nature is presented. A number of appliances and methods specially designed for this research are also described, agreed-on spectrum-photometric and polarization-metric methods, as well as scattering media spectroscopy methods are applied. The principal practical results are (1) a coating is designed for photometric layers that has the best existing spectrum photometric characteristics in the spectral interval 0.35 to 2.0 μm; (2) a number of photometric and polarization characteristics describing the peculiarities of light field formation inside the scattering medium are obtained; (3) some methods of quantitative evaluation of dielectrics and semiconductor roughness parameters, the corrosion injury of steel under opaque protective coatings, and the degree of partide orientation in the scattering medium are suggested; and (4) some instructions for optical methods to control the applicability of different dye staffs to cloth and for determining the temperatures of their usage and decay are elaborated.

Investigations in the field of diffractive optical element (DOE) fabrication using optical methods and registering media based on chalcogenide vitreous semiconductors are reviewed. The peculiarities of the holographic diffraction grating (HDG) fabrication processes using such resists are investigated and the factors that influence the groove profiles are determined. Ways of optimizing media parameters, exposure, and treatment processes are shown. High-quality HDGs are obtained with spatial frequencies in the range 600 to 3600 mm^-1, diffraction efficiencies of 80 to 85% in polarized light, and a stray light level of 10^-6. The processes of Fresnel lense formation by the holographic method with the consequent diffraction pattern transfer into the substrate are developed and investigated. This provides an opportunity to obtain binary lenses with high numerical apertures and small sizes. The results of investigations of the fabrication processes of DOEs with blazed profiles are discussed. Most promising is the method of direct DOE recording using a sharply focused laser beam, which enables one to obtain kinoform elements with m icrometer-sized distant zones. Additional treatment methods (wet or dry) enable one to obtain blazed gratings using the initial HDG with a symmetrical profile fabricated on the base of the chalcogenide layers.

Raman scattering measurements are combined with optical recording on amorphous selenium layers or Se-containing multilayered nanostructures with the purpose of ascertaining the nature and operation possibility of structural phototransformations at different stages or conditions of the recording process.

Real modulation transfer function is developed for a chopper operating pyroelectric camera. Constructive parameter influence on output signal is analyzed.

An approach to designing of all-optical universal integrated-optical logical elements (UIOLEs) for digital optical systems of data processing and transmission based on effects of changing of reference radiation spreading direction under the influence of control radiation is examined. The possibility of construction of multichannel universal logical elements with high-speed programmed tuning on a realized Boolean function is presented. Their throughput may be up to 100 billions of operations/s and higher.

The analysis of the linear and nonlinear optical properties resulting from quantum confinement in CdSSe-doped glasses is reviewed. The growth technology and the data obtained by x-ray diffraction and transmission electron microscopy methods are also reviewed. Analysis of the influence of sizes, composition, and the dispersion of these values on both charge carrier energy and optical (absorption and photoluminescence) spectra is carried out. The peculiarities of the absorption saturation processes related to the quantum confinement, the surface recombination, and the hexagonality of microcrystals randomly oriented in the glass matrix are discussed.

An exciton-phonon mechanism for producing cavityless optical bistability is suggested. We consider the influence of the oscillating subsystem of a crystal on the absorption process of a laser wave in the region of exciton frequencies. It is shown that exciton-phonon interaction leads to nonlinear dependence of the absorption coefficient on the density of the exciton gas. The increase of absorption with increasing exciton density, however, is possible only in the frequency region on the long-wavelength tail of the exiton band. As a result, the exciton density of the crystal becomes a hysteresis function of external parameters (intensity of the incident wave, temperature, etc.). We calculate the absorption coefficient of excitons and define the frequency and temperature regions where optical bistability may exist. We analyze different relaxation mechanisms of excitons and explain the experimental results of observing optical bistability in different semiconductor crystals.

We consider the problem of a holographic associative memory (HAM) which must reconstruct a 2-D optical signal with corrected amplitude errors. The experimental conditions for an associative reconstruction with true brightness tone rendering by a regular HAM based on the ghost-image hologram are determined. More universal all-optical error-correcting (EC) HAMs are also presented and demonstrated. These HAMs perform a reconstruction of the second image of a stored memory that is angularly separated from the readout beam of its partial version. We describe the scheme solution of an ECHAM problem using Denisyuk's hologram, which reconstructs an error-corrected associative response in reflection. Then the original all-optical ECHAM using the so-called quadric hologram (QH) is presented. This term here refers to a thin off-axis nonlinearly recorded hologram used as the matched filter of a regular coherent correlator. When a QH is read out by the partial or distorted version of the stored memory, the complex conjugated associative response is reconstructed at the output plane with an original brightness distribution. A QH-based ECHAM is equivalent in efficiency to nonlinear HAMs based on the resonator architectures using phase-conjugation techniques and external nonlinearities, but it differs from these in arrangement simplicity and implementation flexibility as an EC associative module of the more general neural network architectures.

Wide application of lasers in the optics of scattering media has stimulated interest to wavefront transformation during light propagation in inhomogeneous media, as I noted in a 1981 paper. The vectorial nature of coherent field scattering by rough surfaces is investigated

Monochromatic optical detection is often desired. One technique to accomplish this is to place the detector within an optical resonator. The authors consider the theoretical description of resonant optical detection using an intrinsic semiconductor detector layer placed within a monolithic vertical cavity. The effects of wavelength-dependent index and absorption are included in the analysis. It is found that, unlike passive Fabry-Perot filters, the resonant detector can have a single resonant peak and thus strong suppression of out-of-band light.

The author reports a method for inspection of optical disks based on diffraction measurements. An optical disk has very fine grooves, so that light diffracted from it is spread over large angles, and the change of inclination factor related to Fresnel's coefficients at grooves cannot be ignored. To predict diffraction patterns, Fraunhofer's integral has to be modified. In actual fabrication the groove form may deviate from the ideal rectangular cross section. Moreover, multiple reflections from substrate surfaces can also affect the diffraction patterns. A method is presented to measure the power spectrum of a light beam scattered or diffracted by an optical disk and to recover parameters (pitch, width, and depth of grooves) of optical disks from these power spectra. The wide-angle diffraction problem is solved by taking effects of the inclination factor into account. The effects of groove form and multiple reflections on the diffraction patterns are also included in the theory. To estimate the accuracy of this method, the optical disks were also examined by the SEM technique. The two methods yield results agreeing to 1.9% for the pitch, 5.6% for the width, and 8.6% for the depth.

This paper proposes a variable blaze angle echelette reflection grating applicable to the quasi-optical millimeter wave region with the necessary theory. With our mechanism, the blaze angle can be varied to get the optimum diffraction efficiency for the desired wavelength with the same instrument. Such a grating appears to have promising application in millimeter wave astronomy. Its diffraction efficiency as a function of blaze angle and operating wavelength is obtained.

Dichromated gelatin has been established as the most frequently used recording material for the production of holographic optical elements. New applications are being found for photopolymers in previously unexplored areas such as holographic interconnect systems. However, photographic emulsion from the beginning has been and continues to be the most used holographic recording material. This is due to its relatively high sensitivity and ease of processing, the availability of improved processing chemistries and commercial films, and the repeatibility of the results. We analyze different sources of noise in photographic emulsions (such as intermodulation noise, noise gratings, and nonlinear noise) and the influence of the photochemical process on those noise sources. Bleached emulsions using rehalogenating and solvent processes are considered, and silver-halide-sensitized gelatin is discussed as a medium for transmission holograms. New developers and new noise models are presented on the supposition that the nonlinear response of the recording material is due to the photochemical process.

We present a comparative study between two experimental methods to determine the modulation transfer function (MTF) of a hololens system. The two hololenses were previously recorded and tested for filtering pseudocolor. In the first method we used the classical Foucault test. The second, alternative method is based on the digital image processing of a perfect edge under incoherent illumination. From the digitized intensity line profiles we obtain the MTF and cutoff frequency of the optical system according to the reciprocity between line spread function and MTF. Comments are made on the applicability and accuracy of these two methods.

A holographic microscope with conjugate reconstruction for the interferometric determination of 3-D displacement vectors is described. Three double-exposed holograms of different illumination directions recorded on one hologram plate are reconstructed conjugately, and phase-stepping techniques are used to evaluate the interferograms. Only by conjugate reconstruction it is possible to obtain a perfectly optimized interferometer for the static evaluation method. Using both phase-step and filtering techniques, the evaluation of interferograms greatly disturbed by speckle noise can be performed successfully.

Dichromated gelatin with methylene blue is red sensitive. Tetramethylguanidine intensifies this red sensitivity. Holographic plates covered with such an emulsion were used to investigate the influence of some procedure and development parameters on the structure and diffraction efficiency of holographic gratings. The ratios and concentrations of prehardener, fixer, and sensitizing solution, as well as the pH dependence and storage time, have been investigated. The best results were obtained by a six-step development process. The optimized process needs 3 h from the first step to the final hologram grating. By adapting all investigated parameters, more than 70% diffraction efficiency was achieved. Volume effects in layers of different thickness have been investigated.

We present a spatially and temporally adaptive iterative image restoration algorithm. It extends an earlier technique using row action projection (RAP) by continuously varying spatial adaptation for applying updates and smoothing instead of the earlier segmentation based approach. The new algorithm is a subset of the method of projection onto convex sets and incorporates any a priori information about the blurred image or the blur in order to reduce ambiguity in the solution and accelerate the speed of convergence. Our algorithm generalizes the projection concept to column action projection (CAP). In RAP, an error in the estimate of a pixel of the blurred image is used to update all those pixels of the restored image that contribute to it. In CAP, a pixel of the restored image is updated using the errors in the estimates of all those pixels of the blurred image that receive contributions from that pixel. This algorithm adds a way of emphasizing high-SNR regions during restoration, reducing edge blurs by using a new edge-oriented smoothing, morphologically processing the local variance of the restored image, and temporally varying the restoration parameters to provide significantly better SNR improvements during restoration.

Surface roughness determination is of great interest for many applications. Several methods can be found in the literature, but most of them rely on indirect evaluation of the information, such as photographic techniques. We propose a method to measure surlace roughness that takes advantage of digital speckle pattern interferometry for obtaining the data, and of digital image processing for evaluating it. After defining the problem, a theoretical description is presented, and finally it is compared with experimental results, showing good agreement.

The possibility of improving the focusing effect in laser scalpels employing tapered probes with a novel parabolic form has been studied. The irradiance distribution in conventional conical and parabolic tapered probes has been calculated by 3-D ray tracing in the tangent plane with taper angles 9 and 17 deg and their parabolic modifications. The results are compared with measurements of the light distribution in saline using a CCD camera. The irradiance increase in parabolic probes was four times that observed in conical probes. Laser scalpels with novel parabolic rods will be better for precise treatment of tissue than conventional laser scalpels with conical rods.

To improve overall separation and classification performance for touching handwritten numeral strings, we have to deal with double-touching problems, which occur particularly for some combinations of digits. We propose a strategy to separate single- and double-touching numerical strings. The proposed technique includes: using two-cut links to deal with double-touching problems; using weighted geometric-property measures to rank both one- and two-cut links; and using a rejection scheme to reject poor links at both ranking and recognition stages. Two-cut link pairs that join the high-curvature points in inner contour(s) to those in the external contour are considered when all one-cut links that join the upper and the lower external contours fail to separate them. All combinations of one- and two-cut links are ranked according to weighted geometric-property measures, and the top links are chosen and tested by the recognition system. Experimental results on the National Institute of Standards and Technology database show that our system for solving both single- and double-touching problems compares favorably with the other techniques tested.

A photorefractive joint transform correlator is connected to a PC-based image processing board and tested for fingerprint recognition. Distortions due to rotation, scale, and partial hiding are considered: ± 4 deg in rotation, ± 7% in scale, and up to 80% hiding can be handled by the correlator. The performance of the correlator operating with a realtime fingerprint acquisition camera is then measured. The captured fingerprint is generally distorted with respect to its original counterpart stored in the PC memory. These distortions are mostly due to the positioning and pressure of the finger on the glass prism of the camera. We evaluate the recognition performance qualitatively and statistically with these distortions on a limited data bank and demonstrate 80% successful recognition rate.

Subsurface probing of inhomogeneous dielectric media has received considerable attention from the research community. Extensive work in this area has been presented either in the time or frequency domain. However, most of the algorithms presented are mainly devoted to continuous dielectric profile inversion. The fast Fourier transform (FFT) inversion method is newly introduced for discrete multilayer inversion. This method has the advantages of simplicity, a short computation time, and robustness with respect to noise. The FFT inversion method is applied to a discrete homogeneous multilayer dielectric model using oblique incidence and a limited bandwidth, provided that all dielectric media are lossless and nondispersive. For a given model, a uniform plane wave is obliquely incident on the top of its surface, with its polarization being either a transverse electric or a transverse magnetic wave. In each case, the corresponding reflection coefficient is sampled over a finite frequency range. The time-domain spectrum of the reflection coefficient is obtained by applying the FFT algorithm to its samples. An algorithm is developed for the deduction of the height and permittivity of each layer. The algorithm is tested by using the simulated data of a three-layer half-space dielectric model. The resulting relative errors in the inversion process are almost less than 10^-4 for all of the model parameters. When a random noise signal is superimposed on the sampled input data, the relative errors are comparable to the noise-to-level ratio.

A method for invariant pattern recognition of range images by means of the phase Fourier transform is introduced. The phase Fourier transform may be used for the segmentation of connected planar and quadric surfaces. The method is generalized to nonconnected planar surfaces through the use of the concept of the characteristic normal. An invariant representation under changes of position, scale, and orientation for the characteristic normals is defined. This representation is used as the input for a feedforward neural network. Examples of applications are given, and finally the method is applied to the problems of classification and occlusion.

The response of a self-pumped phase-conjugate mirror to spatially nonuniform phase change of incident wave is examined with a phase-conjugate Fizeau interferometer. The experimental results make it clear that the spatially nonuniform phase change of the incident wave is not reversed by the self-pumped phase-conjugate wave (SPPCW) immediately after the phase change, and the decrease of phase-conjugate reflectivity caused by the nonuniform phase change is proportional to the nonuniformity of the phase change. The phase characteristic of the SPPcw makes the phase-conjugate Fizeau interferometer for surface profile measurements insensitive to object vibrations. The reflectivity characteristics enable us to measure the nonuniform phase change by detecting the intensity of the SPPCW.

In light of the principle of phase matching (PM) in biaxial crystals, PM types for four-wave interaction processes are discussed. The relationships among the refractive indices of the four interacting waves are analyzed to classify PM topologies. A computer program is developed to characterize and obtain PM directions and their loci. As examples, PM loci for direct third-harmonic generation in four biaxial crystals are presented.

A new method using an atomic-resonance filter and deconvolution techniques has been developed to acquire high-resolution spectra of atmospheric Rayleigh-Mie scattering. In the deconvolution process, the difticulty of the undetermined division 0/0 is overcome by a fitting method. Preliminary laboratory experimental results on 90-deg scattering show that with a signal-to-noise ratio of 20, the scattered Rayleigh-Mie spectrum may be retrieved in agreement with the theoretical analysis.

An experimental analysis has been made of the light scattering from particulate surfaces as a function of the surface particle density. The samples were composed of a conducting flat substrate seeded with spherical metallic particles whose radius is on the order of the wavelength of the incident radiation (λ = 0.633 μm). We analyze how the multiple-scattering effect evolves as the separation between particles changes. From a theoretical point of view, we have applied a ray-tracing method to obtain the scattered intensities. These were compared with the experimental results. Good basic agreement was found, especially in the backscattering region.

An effort to quantify effects of weather in the northern Negev desert on airborne particle concentration and on cross-sectional area per unit volume, so as to permit prediction according to weather, has begun. Correlations of prediction with measurement are on the order of 94% and 91%, respectively. Humidity is the dominant weather parameter, as expected, but it is not the only parameter. There is statistical significance too to solar flux, air temperature, and wind speed. The empirical model here provides a means of comparing theoretical models of effects of weather on airborne particle statistics with real-world phenomena. It is suggested that these models may well be applicable elsewhere, since the newly airborne particles are only a small fraction of the total airborne amount.

We present a nondestructive, high resolution optical technique to obtain the surface topography of ancient paintings. The method is based on the projection of a grid of parallel lines, using white light, onto the surface to be analyzed. When viewed at an angle different from the projection angle, the grid pattern appears deformed by the surface shape. This pattern is digitized and then processed using a spatial-carrier phase-shifting algorithm that allows recovering the surface height map with high precision. The method relies on very simple equipment, gives immediate quantitative results, and is suitable for in situ measurements. It permits the recording of topographic maps of ancient paintings as well as the measurement of local detachments of the paint layer. A theoretical analysis of the method is discussed, together with a description of the data analysis algorithm. Finally, we provide some experimental results concerning the diagnostic of a twelfth-century masterpiece.

A new method for measuring vibrations using a quadrant position sensor has been developed. It allows noncontact measurement of natural frequencies of objects that are transparent and small or lightweight, such as dragonfly wings. It simultaneously measures natural frequencies in two dimensions without any reflective mark having to be placed on the object. The system consists of a laser light source, a quadrant position sensor, and a spectrum analyzer. The object is illuminated by divergent laser rays coming from a microscope objective lens. The vibration amplitudes of the object are magnified and detected by the position sensor. By adjusting the distance between the object and either the lens or the sensor, the sensitivity and linearity of the system can be changed to measure objects of different size. We measured the natural frequencies of a dragonfly wing along the chord and the span, using a vein as a mark to measure displacement during vibration. This allowed us to determine the natural frequencies of bending and torsional deformation. Our results show that this two-dimensional, noncontact method can be effectively applied to the field of millibioflight.

We present a new method to estimate the wavefront with the curvature-sensing technique proposed by F. Roddier. Instead of solving a Poisson equation for the curvature signal, we estimate the wavefront by direct least-squares curve fitting of the curvature signal with derivatives of Zernike polynomials. It is computationally simpler and faster. From computer simulations, it is shown that the curve-fitting method gives quite accurate wavefront estimation. It is especially useful when only a fixed number of aberration modes are of interest, as in the optical-axis adjustment of a telescope.

Optical wavelet transformation is implemented with a volume hologram in the frequency domain. The 2-D Haar wavelets of different types and with different dilation factors are encoded with a polarizer, and their Fourier spectra are recorded in a volume hologram with an angular multiplexing technique. Different local features (such as corners and edges) of an input image are extracted simultaneously by the corner and edge Haar wavelets. Experimental results and computer simulation are compared and presented. The limitations and the feasibility of the system are discussed.

This PDF file contains the letter “Letter: Comment on the paper” for OE Vol. 34 Issue 04

This PDF file contains the editorial “Book Rvw: Integrated Optics: Design and Modeling," by Reinhard Marz for OE Vol. 34 Issue 04