One of the great pleasures in being your editor is that it keeps me in constant touch with colleagues around the world as we pursue our scholarly and technical work in optical science and engineering. Our family of authors, guest editors, reviewers, and readers is the international team who defines the discipline of optical science and engineering.

I agreed to be the guest editor of this special section with mixed feelings because I am only interested in optical materials from the designer’s point of view. I think that problems of materials science, which deals with properties of materials and how these properties are determined by a material’s composition and structure, are less substantial for readers of Optical Engineering. However, I carried out many discussions with potential contributors to focus the papers’ themes for this special section on practical and technical problems that are useful for engineers, and I hope I have succeeded in doing so.

High-power, high-energy laser (HEL) systems include an optical train consisting of mirrors and windows, which must be capable of transporting and directing the beam without seriously degrading the nominal performance. Since catastrophic failure modes are not a major threat at beam-power levels of current interest, the system’s performance as measured in terms of achievable target irradiances may degrade as a result of thermal lensing, that is, the wavefront distortion caused by thermally induced phase aberrations. Analytical investigations that address the problem of evaluating the nature of laser-driven mirror/ window distortions are reviewed and updated. In this context, a method is proposed for obtaining simple figures of merit (FoM) for rating the thermal lensing performance of mirror-substrate materials as well as window-material candidates. The performance of cooled HEL mirrors reflects their ability to minimize irradiance-mapping wavefront distortions, which leads to defining a thermal distortion coefficient j that controls the out-of-plane growth of the faceplate. It is then straightforward to derive equations for characterizing the root mean squared surface deformation and to assess the merit of mirror-faceplate materials in a pulsed or a cw environment. Since state-of-the-art heat exchangers exhibit relatively modest Biot numbers, the thermal conduction is not a critical parameter but the modulus of elasticity must be properly factored into the FoM for cw operation. Window-induced wavefront deformations require special attention because they involve not only position-dependent variations of the window thickness but also position- and polarization-dependent variations of the refractive index. This situation leads to introducing symmetric and antisymmetric distortion coefficients, which can be combined into an effective optical distortion coefficient x that specifies the relative weight of birefringence compared to all other sources of distortion and shows that zero distortion can be achieved only with stressbirefringence- free material having a negative dn/dT. As in the case of mirror-faceplate materials, FoMs for the prediffusion and the steadystate regimes emerge in a direct manner and demonstrate that fluorozirco- aluminate glass by far outperforms other window-material candidates in implementing the zero-distortion goal.

Three thermal effects—variation of image location, variation of focal length and longitudinal chromatism—are described in the form of formulas, which include surface distributions proportional to the thermal constants. Principles for the optical system athermalization by means of optical (passive) compensation and thermooptical (active) compensation are given. The problem of proper selection of thermal material constants and mechanical constants of lenses and mounts is discussed. The condition for achromatization in the form of the formula including material distributions and the principle of material selection is given.

The thermointerferometric method for the investigation of materials and thermo-optical phenomena is presented. It makes it possible to determine the thermal interaction-surface deformations and changes of optical properties of objects subjected to thermal load. The method is based on the registration of the temperature distribution on the object surface using a thermovision camera and simultaneous interferometric measurement of the wavefront reflected from the front surface or transmitted through the object. The latter measurement monitors the changes of the surface shape and its optical properties. The experimental setup is presented as well as the methodology of data acquisition, evaluation and presentation. Some considerations of the range of applications and perspectives are also given. These are based on the analysis of experiments verifying the application of the method to investigation.

Homogeneous lens material is characterized by an index of refraction and a point on the glass map n/d=f (y d). Gradient refractive index (GRIN) lenses have a spatially varying index and dispersion and are represented by a line on the glass map. GRIN lenses open the door to a wide variety of optical design applications incorporating entire lenses of axial gradient refractive material (macro-AGRIN). Axial gradient material essentially gives biaspheric behavior to lenses with spherical surfaces and exhibits a controlled gradient in both index and dispersion. Thus, the applications for this material range from simple singlet lens used for imaging laser light, in which spherical aberration is eliminated, to complex multielement lens systems, where improved overall performance is desired. The fusion/diffusion process that produces this material is surprisingly simple, repeatable, and applicable to mass production. The advantages of AGRIN technology coupled with the recent advances in material development and its accessibility in commercially available lens design programs provides optical designers with the opportunity to push the performance of optical systems farther than with conventional optics.

Gradient-index lenses have been made from phosphate glass containing silver by exchange of Ag1 ions from glass for Na+ ions from salt. A lens with a parabolic profile of a refraction index and a diameter of 7.26 mm is produced. For this lens, maximum ?n is 20.032.

The possibilities of producing waveguide structures in glass using the ion-exchange technique are discussed. The modeling of particular sequences of the technological process with respect to planar and strip waveguide structures as well as refraction profile measurement results for these waveguides are presented. An exemplary application of this technique in the construction of planar sensors is also presented.

The results of scientific and technological experiments performed in the Glass Department of the Institute of Electronic Materials Technology in Warsaw are presented. Research on fiber optic elements are carried out in areas of light and image guides made of multicomponent glasses and light guides made from pure silica glasses. The laboratory methods of manufacturing the glass elements, which are the starting preforms for optical fibers are elaborated. These methods include selection of the proper chemical composition of glasses, preparation of optimum material batches, melting the glasses in platinum or ceramic crucibles, mechanical working (grinding and polishing) of glass blocks to obtain rods for rod-in-tube preforms. Methods of pulling glass fibers of different cross sections for several medical, technical and environmental applications are improved. A high level of techniques and technological skills in the manufacture of optical fibers make it possible to obtain a higher generation of optical fiber elements and possibly to transmit an image.

Halide-chalcogenide glasses whose properties make them suitable for applications in modern optics and optical fiber technique are investigated. The object of examination were oxygen-free glasses in the Sb2Se3-BaCl2-PbCl2 system. Because of the unconventional method of obtaining these glasses (great difficulties connected with passing into the glassy state) a special method of synthesizing these glasses is developed. Their characteristic temperatures and thermal stabilities are determined. Structural investigations using IR spectroscopy are carried out and the phase composition following the crystallization of the glasses is established by x-ray examination. Certain properties of the glasses are investigated, giving special consideration to the optical properties (refractive index and transmission in the far-IR range). The investigation results reveal the possibility of producing stable glasses, a few millimeters thick, using a special method of synthesis. The absorption bands in the IR spectra of the examined glasses are attributed to the symmetric and asymmetric vibrations of the Sb-Se-Sb bridge. The transmission range of the obtained glasses falls within the limit 0.65 to 50 ?m, at the level of 38 to 60%, and the refractive index is n > 2.5. Material of such properties offers the possibility to obtain optical fibers of very high numerical aperture and special applications are possible because of a wide transmission range.

The results of the investigation of new kinds of amorphous glassy materials, the methods of their preparation, and their properties with a view of applying them in modern optics and light fiber techniques are presented. As a result of a change in the chemical composition and the applications of special synthesis techniques, it is possible to change the optical, spectral, technological, and other properties of glass. The objects of the investigation were the oxide, halide, chalcogenide-halide, and mixed glasses. The problem of the structural changes in particular kinds of glasses as related to the changes in their properties is discussed. The possibility of the application of glasses transmitting IR radiation is also discussed.

The optical properties of fluorozirconate glasses are determined. The composition of glass selected for investigation is 58ZrF4, 36BaF2, 6LaF2, 10AlF3, 10NaF. The light transmittance of the glass falls in the range from 0.23 to 7.5 ?m. The mean dispersion of the examined glass is the same that of water, 0.0065, and the Abbe number is 77. A very important advantage of fluorozirconate glass is the fact that it satisfies the condition of adjusted interferometry when water is the immersion medium.

The mechanical, thermophysical, spectroscopic, nonlinear, and laser properties are presented for one of the most efficient laser crystals: neodymium-doped potassium gadolinium tungstate, KGd(WO4)2:Nd3+-(KGW:Nd). Nonresonance and optical properties are also presented.

An Nd:glass laser system is described that enables smoothly varying the pulse duration of single-frequency laser radiation in the range from 0.2 to 30 ns and focusing the beam to spot sizes from 0.4 ?m at high reproducibility of spectral and spatial-temporal parameters of radiation. This laser system is used to examine the nonlinear photoinduced processes and laser-induced damage in chalcogenide glasses under high-power laser radiation in the near-IR spectral range. It is found that photoinduced losses (absorption and scattering) are produced in chalcogenide glasses by high-power laser radiation with photon energy hv < Eg . The exposure results in both reversible and irreversible structural transformation of these glasses in the exposed region. The reversible darkening is similar to the known effect of photostructural transformations in thin films exposed to photons with energy higher than the glass bandgap. The irreversible contribution is connected with the photoinduced localized destruction of bulk material. It is believed that the process of local destruction is connected with the nonlinear excitation of the structural irregularities randomly distributed in the glass.

The operating principles of electro-optic and photorefractive spatial-temporal light modulators (STLMs) having electrical and light control are considered. An analysis of the characteristics of STLMs shows that they make it possible to carry out basic mathematical operations on 2-D optical signals in real time as well as providing for the entry, processing, and display of information. The presence of an optical memory for information in the form of images makes it possible to carry out multichannel spectral analysis of ratio signals, multichannel correlation, pattern recognition, etc.

A one-dimensional physical model of a linear three-channel bulk charge-coupled device (BCCD) with a surface n channel and bulk channels of n- and p-type conductivity is considered. The system of three nonlinear differential equations describing the process of BCCD photorelaxation is obtained. On the basis of these equations, the numerical simulation of the process of photorelaxation under the influence of the absorption of optical radiation with uniform spectral intensity characteristic (0.4 ? ? ? 1.1?m) has been performed for a silicon three-channel BCCD. Spectral characteristics of the channel photosensitivities have been calculated, and the resulting selectivity of intrinsic radiation absorption is found. The maxima of spectral photosensitivity full at 0.5-, 0.67-, and 0.83-?m wavelength for the surface n channel and bulk n- and p-type channels respectively. Typical values of photorelaxation time are 1 to 0.6 ms at power density of absorbed radiation ? 100 ?W/cm2. The calculations have been performed for a three-cycle time diagram of the control voltage pulses of the following levels: upper level + 22 V, lower level + 2 V, and midlevel + 8 to 12 V. The results of simulation allow us to consider a three-channel silicon BCCD as a monocrystal spectrosonal photoelectrical image converter.

A new phase unwrapping algorithm based on reliability and edge detection is presented. Since the edge is detected efficiently through edge relaxation, the unwrapping procedure is simplified within the areas embraced by edges. Penetrating edges according to reliability ensures that this method will limit the unwrapping error to local-minimum areas at worst.

We previously (1995) proposed a novel recording method to reduce the crosstalk noise and improve the storage capacity in anglemultiplexed volume holographic data storages. Instead of conventionally using a plane wave (point reference) to record holograms, the technique employs a recording reference extending uniformly within a narrow spatial frequency bandwidth and reads the memory with a plane wave. The analytical results show that the SNR obtained by using the extended reference method is about 20 dB higher than that achieved in terms of the conventional recording method. For interpixel crosstalk noise, a statistical analysis is presented and the SNR is given in a closed form for both the point reference and the extended reference methods. Considering both interpage and interpixel crosstalk noise, we further investigate the crosstalk-limited storage density. The results show that the proposed extended reference method achieves about 10 times larger storage density than the point reference method.

A novel device, the nonspatial filter, is described for laser beam cleanup. It is based on the Bragg selectivity of thick holograms. Unlike pinhole and fiber spatial filters, which employ lenses and apertures in the transform plane, nonspatial filters operate directly on the laser beam. This eliminates the need for laser beam focusing, which is the source of many of the material and alignment instabilities and laser power limitations of spatial filters. Standard holographic materials are not suitable for this application because differential shrinkage during processing limits the maximum Bragg angle selectivity attainable, and because they are generally too thin. New technologies that eliminate the problem of differential shrinkage are described. These technologies are based either on the use of a rigid porous substrate material, such as porous glass, filled with a light-sensitive material, such as holographic photopolymers or dichromated gelatin, or on the use of a thick photopolymer with diffusion amplification (PDA). We report results of holographic nonspatial filtering of a laser beam in one dimension, with an angular selectivity of better than 1 mrad

A proposal for an image distortion compensation and perspective correction method for a rainbow-type color conical holographic stereograms is presented. The image processing method is accomplished through ray-tracing equations. The approach taken consists in applying an image process to the original set of images to generate a new set of 2-D images. Using this method, the original object perspective is recovered and a full color image without distortion is displayed at the center of the conical holographic stereogram.

We propose a new method to improve the image quality and the encoding time of tree-structured vector quantization (TSVQ). We call this new method the closest-coupled tree-structured vector quantization (CCTSVQ). In this method, we use the closest-neighboring pointers to enlarge the search range of each search path and guide all search paths into more appropriate codewords. CCTSVQ therefore improves the image quality of TSVQ. This fact is shown in our experimental results. Furthermore, in these experimental results, we see that the encoding time of CCTSVQ is always faster than that of TSVQ, based on the same image quality.

In automated manufacturing systems an important task is to recognize different three-dimensional objects, e.g., workpieces. For this purpose we have used the fact that different objects scatter laser light from a scanner differently. To recognize the differences between the light reradiated by the objects we have used Fourier transformation. By this means the scanned data can be reduced to a few parameters for classification of the objects. This method is a rather simple and inexpensive way to complement other object recognition systems, e.g., in robotic applications. Both theory and verifying practical tests and results are presented.

Quantitative assessments on the performance of automated cloud analysis algorithms require the creation of highly accurate, manual cloud, no cloud (CNC) images from multispectral meteorological satellite data. In general, the methodology to create these a priori analyses for the evaluation of cloud detection algorithms is relatively straightforward, although the task becomes more complicated when little spectral signature is evident between a cloud and its background, as appears to be the case in advanced very high resolution radiometer (AVHRR) imagery when thin cirrus is present over snow-covered surfaces. In addition, complex procedures are needed to help the analyst distinguish between water and ice cloud tops to construct the manual cloud top phase analyses and to ensure that inaccuracies in automated cloud detection are not propagated into the results of the cloud classification algorithm. Procedures are described that enhance the researcher’s ability to (1) distinguish between thin cirrus clouds and snow-covered surfaces in daytime AVHRR imagery, (2) construct accurate a priori cloud top phase manual analyses, and (3) quantitatively validate the performance of both automated cloud detection and cloud top phase classification algorithms. The methodology uses all AVHRR spectral bands, including a band derived from the daytime 3.7-?m channel, which has proven most valuable for discriminating between thin cirrus clouds and snow. It is concluded that while the 1.6-?m band is needed to distinguish between snow and water clouds in daytime data, the 3.7-?m channel remains essential during the daytime to differentiate between thin ice clouds and snow. Unfortunately this capability that may be lost if the 3.7-?m data switches to a nighttimeonly transmission with the launch of future National Oceanographic and Atmospheric Administration (NOAA) satellites.

A regularized image restoration model in multiresolution spaces is proposed. The image is transformed in the wavelet domain, and the restored image is found as the solution of a constrained meansquared- error optimization. The image energies in the subbands of a wavelet decomposition of the image set the constraints of the optimization problem. A closed-form relationship of the image energy in the wavelet channels is derived. The restored image is obtained by solving iteratively the equation that sets the derivative of the error norm equal to zero. The Lagrange multiplier that corresponds to a subband is given as a function of the noise and the image energy in the subband. Results of numerical experiments on multiresolution image restoration using one and nine constraints, respectively, are presented and compared against image restoration results obtained from a conventional regularized image restoration algorithm that is based on generalized cross validation and uses the Laplacian operator as the smoothing filter. The experimental results obtained by the proposed method indicate that the restored image is closer to the original if one solves the restoration problem using more than one smoothing filter.

Sampling-limited resolution in a two-dimensional infrared focal plane array is discussed in terms of the reciprocal (inverse) lattice in the frequency domain. It is shown how the bandwidth of the signal that can be reconstructed without error can be increased by a microscan. Microscanning means translating the image over the detector array along a short distance and then resampling the image, thus increasing the spatial sampling rate by decreasing the distance between samples. Two current microscan modes are compared: the rectangular bidirectional mode, in which the image is translated by half the array’s pitch along the two main perpendicular axes, and the diagonal mode, in which the image is shifted by half the diagonal of a rectangle defined by four adjacent pixels. It is shown that the diagonal mode implies the same frequency limit in accordance with the Nyquist criterion, in the horizontal and vertical directions, as the bidirectional mode. The temporal MTF that is a result of the microscan is calculated for the case where the temporal impulse response is a one-sided exponential pulse, like the thermal response of uncooled IR detectors. A simple algorithm for the reconstruction of the diagonal-microscan sampled data is suggested, and its MTF is derived.

A new optical method for angle measurement based on totalinternal- reflection heterodyne interferometry is presented. In this method, heterodyne interferometry is applied to measure the phase difference between s and p polarization states at total internal reflection. This phase difference depends on the angle of incidence. Hence, smallangle measurement can be performed only by evaluating this phase difference. The validity of the method is demonstrated, and it has a measurement range of 10 deg. Its resolution depends on the angle of incidence; the best resolution is 8×10-5 deg.

A recently introduced wavefront analyzer, based on a Fresnel-lens array, is improved by incorporating phase-shifting procedures. The resulting compact and stable interferometer can measure wavefront distortions with extremely high accuracy. In our experiments, with no special efforts at environmental isolation, the instrumental noise level was under 0.02?.

A simple and rapid dynamic experimental determination of the photorefractive and absorption coupling factors are presented. The experimental measurements were made during the sinusoidal grating decays that occur by interrupting one of the beams, after the real time grating formation, in a two wave mixing holographic setup. The proposed method is based on the effective dependence of the writing and probe beams polarizations, along the interaction between absorption and photorefractive gratings. All experiments were carried out in the diffusion only recording mechanism, that is, no external electric field is applied to the sample, for which we used the photorefractive crystal Bi12TiO20, illuminated by ?=50.633 ?m from a He-Ne laser light source.

The optical memory effects of the newly developed sol-gel gel-glass based thermochromic material are studied. Several fundamental material parameters, which contribute to the formation of two stable states in this substance are quantitatively measured. Simple writing and erasing methods along with the long term stability of each memory state are demonstrated.

We discuss a new detection scheme to measure very small angular deflections of a Gaussian beam. We show that it is possible to increase the sensitivity to angular deflection substantially in comparison with the conventional optical beam deflection method (OBDM). It is shown that the theoretical limit to the minimum detectable angle when the detection is assumed to be shot-noise-limited may be improved accordingly. A detailed analysis of the conventional OBDM for the purpose of comparison is also presented. A proof-of-principle experiment is described, and some experimental results are given.

The authors discuss the use of spectral pattern recognition techniques to distinguish color camouflage from green vegetation background. Here, the spectral feature is taken as the basic characteristic for recognizing the target. We have measured many reflected spectra of state-of-the-art green camouflage material and green vegetation, analyzed their spectral pattern regularities, and found the optimum features for recognition. The classification results are very satisfactory.

We propose a general and fully automated procedure that enables the self-correction of the errors and performance losses produced by the misalignment of the components of an optical correlator. This method is simple, is carried out entirely by software, and has minimal operating constraints. There are no moving parts and no extra hardware is required.

A novel technique for photon correlation measurements, based on the excitation of a resonant system by photon-detector single pulses, analog/digital sampling, and deconvolution, has been developed and analyzed experimentally and by computer simulations. The measured correlation function is expressed by a convolution of the true photon correlation function of the optical field and a well-defined, noiseless resonator correlation function. The effect of detector statistics is reduced to the contribution of two integral parameters—the total single-pulse charge and the jitter of single-pulse centers. Good performance of this technique is demonstrated at high photon rates and resolutions, where the well-known photon-counting or single-quantum methods are ineffective. The novel technique offers linear recording of photocount time series without dead-time effects. The temporal resolution is defined by the sampling step of the analog/digital converter. The retrieval error does not exceed 1 to 3% at count rates higher than 1 GHz and single-pulse durations larger than the resolution cell. This technique can be effectively applied in photon correlation measurements of high dynamic optical fields.

An improved phase algorithm for phase-measuring profilometry (PMP) is presented. In comparison with the traditional algorithms, it can remove the influence of the carrier frequency before unwrapping and slow down the variation of the phase. This new algorithm makes the procedure of phase unwrapping easier and more automatic. It is especially suitable for PMP with a high-frequency grating.

Optical ray tracing permits realistic simulations of light images to be produced by calculating the intensity and color of each individual light ray that is projected into a predefined scene. This paper presents a similar technique for the simulation of sidescan sonar images of underwater environments that are generated by the use of acoustic signals. The inherent properties of light in air and sound in an underwater environment produce several fundamental differences between the two techniques, mainly as a result of the temporal display of the sonar images. This paper investigates these differences, presents the basic methodology of the sonar simulation model, and illustrates the techniques used to circumvent the time-based display problems. Finally, some results obtained using this technique are presented.

Recently, multilayer neural networks (NNs) have been used to compress still input pictures.1–8 The first NN to be used for this purpose was described by Cottrell, Munro, and Zipser (CMZ),1 who used a simple (single-structure) fully connected three-layer NN. The CMZ NN has a low computational complexity but only moderate compression performance.*

Recently, multilayer neural networks (NNs) have been used to compress still input pictures.1–8 The first NN to be used for this purpose was described by Cottrell, Munro, and Zipser (CMZ),1 who used a simple (single-structure) fully connected three-layer NN. The CMZ NN has a low computational complexity but only moderate compression performance.*

Have you noticed that there are so many new optical microscope technologies that they are starting to steal each other’s acronyms? Do you suspect that you could solve your problems better with an AC Zernike phase-contrast scanning microscope, but you don’t know what that means? The book under review will help you sort out this exciting field. It is both an introduction to and a review of many new optical microscope technologies.