This PDF file contains the editorial “Editorial: A Matter of Citation” for OE Vol. 34 Issue 06

This PDF file contains the editorial “Guest Editorial: Polarization Analysis and Measurement” for OE Vol. 34 Issue 06

When photoelastic modulators (PEMs) are used with lasers as light sources, modulated interference effects may appear as spurious signals at the fundamental and harmonic frequencies of the PEM. They are correlated with the modulator reference signal and are at precisely the same frequencies as the polarization modulation effects being studied. This modulated interference does not appear to be a problem with any light source other than lasers. The modulated interference effects arise because of interference between light reflected at the surfaces of the modulator optical element and the primary beam and relative motion of these two surfaces synchronized with the modulator oscillations. Interference in modulator optical elements, which is similar to multiple beam interference in thin films, is examined. Criteria for estimating the strength of the modulated interference are presented and a simple test for the presence of modulated interference in an optical system that includes a PEM is described. Several strategies are presented for reducing or eliminating these troublesome effects including (1) careful positioning of the PEM, (2) use of antireflective (AR) coatings, and (3) techniques that physically separate the primary beam from multiple reflected beams. Data are given for suppression of the modulated interference by using AR coatings and for one method of beam separation.

Contours of constant principal angle Φ and constant principal azimuth Ψ for an in-line, symmetric, three-reflection mirror system are presented. The three mirrors are assumed to be uncoated substrates of the same homogeneous isotropic material with complex relative dielectric function ε. By assigning values to Φ from 45 to 85 deg in 5-deg steps, the constraint on complex ε is determined numerically and represented graphically. The special case of Φ = 45 deg, which applies to a right-angle parallel-mirror beam displacer, enables an analytical solution. These results have important applications for the production of circular polarization over the entire spectrum, and especially in the VUV, where transmission-type devices are not possible. The performance of the three-mirror system as a VUV quarter-wave retarder/circular polarizer using different metals is also considered.

The design and operation of a Mueller matrix imaging polarimeter is presented. The instrument is configurable to make a wide variety of polarimetric measurements of optical systems and samples. In one configuration, it measures the polarization properties of a set of ray paths through a sample. The sample may comprise a single element, such as a lens, polarizer, retarder, spatial light modulator, or beamsplitter, or an entire optical system containing many elements. In a second configuration, it measures an optical system's point spread matrix, a Mueller matrix relating the polarization state of a point object to the distribution of intensity and polarization across the image. The instrument is described and a number of example measurements are provided that demonstrate the Mueller matrix imaging polarimeter's unique measurement capability.

Four types of polarizers are experimentally evaluated and compared for the uniformity of their transmission axis orientations and the contrast ratio and their spatial variation. Representative samples of calcite Glan-Thompson polarizers, polarizing beamsplitters, silver glass polarizers, and stretched polymer polarizers are characterized at 850 nm using a rotating polarizer imaging polarimeter. The sample Glan-Thompson polarizers show the highest contrast ratios and greatest uniformity of transmission axis. Silver glass polarizers and stretched polymer polarizers show intermediate contrast ratios, but all samples of both show a systematic variation of the transmission axis orientation with a magnitude of several tenths of a degree. The polarizing beamsplitter cube samples have very good uniformity of transmission axis but the smallest contrast ratios with noticeable spatial variations of contrast.

Although zero-order quartz waveplates are widely used in instrumentation that needs good temperature and field-of-view characteristics, the residual errors associated with these devices can be very important in high-resolution polarimetry measurements. How the field-of-view characteristics are affected by retardation errors and the misalignment of optic axes in a double-crystal waveplate is discussed. The retardation measurements made on zero-order quartz and single-order "achromatic" waveplates and how the misalignment errors affect those measurements are discussed.

When a static magnetic field perpendicular to the propagation direction of a laser beam is applied to a magnetic liquid, linear birefringence and dichroism can be present in this material (dichroism appears only for particular preparation conditions of ferrofluid samples). Linear birefringence is used to realize an adjustable wave plate for polarimetric modulation applications in active imagery. A set of linear birefringence measurements are made using a continuous laser source and the results show the possibility for such a material to realize polarimetric modulation, but with inhomogeneities induced by temperature effects. To extend the utilization of such polarimetric property in active imagery, the spatial distribution of this polarimetric characteristic must be homogeneous. A measurement method is developed in the case of an imagery application using a pulsed laser beam; in this case, the temperature effects that could appear with a continuous laser source are removed. The results show the possibility to develop ferrofluids as homogeneous adjustable wave plates for which it is possible to obtain polarimetric modulation for different wavelength.

A commercial PLZT modulator is characterized at wavelengths from 0.6328 μm to the limits of its IR transmission around 9 μm. Laser polarimetry and IR spectropolárimetry are the characterization techniques used. Polarization measurement results include diattenuation and retardation. The PLZT modulator is found to be an electrically controllable polarizer as well as an electrically controllable retarder.

A novel technique for measuring the polarization light scattering function of surfaces using a Mueller matrix imaging scatter polarimeter is presented. This technique measures the near-specular scatter of reflective surfaces as Mueller matrix images, enabling the diattenuation, retardance, and depolarization of the scattered light to be determined. An example of measurements of a diamond-turned aluminum mirror with an rms roughness of 11.4 nm is presented and interpreted. The most surprising result in our data was that this scattering process created partially elliptical polarized light from unpolarized incident light, where we had expected essentially partially linearly polarized light.

We consider the application of the general theory of unitary matrices to problems of wave scattering involving polarized waves. Haying outlined useful parameterizations of the low dimensional groups associated with these unitary matrices, we develop a general processing strategy, which we suggest has application in the extraction of physical information from a range of scattering matrices in optics. Examples are presented of applying the unitary matrix structure to problems of single and multiple scattering from a cloud of random particles. The techniques are best suited to characterization of depolarizing systems, where the scattered waves undergo a change of degree as well as polarization state. The degree of disorder of the system is then quantified by a scalar, the polarimetric entropy, defined from the eigenvalues of a scattering matrix that ranges from 0 for systems with zero scattering to 1 for perfect depolarizers. Further, we show that the unitary matrix parameterization can be used to extract important system information from the eigenvectors of this matrix.

It has been well recognized that, if the incident electromagnetic wave is linearly polarized parallel or perpendicular to grooves of a surface, the far-field scattering from a 1-D rough surface will have an identical polarization. We present recent experimental results and the comparative theoretical analysis that cover the enhanced backscattering from a characterized randomly rough 1-D vacuum/dielectric interface for p and s polarizations. It is believed that the observed enhanced backscattering results from the coherent interference of multiply scattered optical paths with their time-reversed partners when the wave vectors of the incident and scattered light are oppositely directed. This coherency is lost for scattering into directions other than the retroreflection direction.

A unified formalism for polarization optics is presented. This formalism was developed to use the Stokes-Mueller matrix equation and the Lorentz group to provide a conceptual framework and a systematic method to model and understand complicated polarization phenomena in optical media (such as optical fibers, fiber systems, devices, and networks). Central to this approach is the utilization of operator and group theoretic techniques to exploit the analogy that exists between the dichroism and birefringence elements of the Mueller matrix of polarization optics and the boost and rotation generators, respectively, of the Lorentz transformations of special relativity. This formalism incorporates the other popular [i.e., the Jones, the coherency (or density), and the Mueller matrix] polarization approaches into a single unified formalism. To address polarization issues for complicated systems, we introduce several rudimentary deterministic Mueller matrices. First, the Mueller matrix for arbitrary birefringence and dichroism is given. Second, the Mueller matrix for arbitrary but uniform birefringence and dichroism is given. Third, the Mueller matrix for optical media with successive (series) birefringence and dichroism along the optical path are given. Fourth, the Mueller matrix for optical media with simultaneous (parallel) birefringences and dichroisms along the optical path are given. Finally, the formalism is applied to a comparison between polarimetric data [for a short (~ 1 m) optical fiber with low internal linear birefringence under the influence of a constant external twist rate] and a theoretical model. The agreement between measurement and theory are excellent.

Polarization ray tracing is a collection of methods that extends geometrical ray tracing allowing the calculation of the evolution of polarization states along ray paths and the determination of the intrinsic polarization properties, such as diattenuation and retardance, associated with ray paths. The suitability of the Jones, Mueller, and threedimensional polarization ray tracing calculi are compared, examining the issues of local versus global coordinates, amplitude versus phase representations, inclusion of the wavefront aberration function, partially polarized light, measurements of images by polarimeters, and diffraction image formation by low- and high-numerical-aperture beams.

The fundamental quantity used to describe radiative transfer is the radiance or specific intensity. For unpolarized descriptions of surface scattering, the radiance is used in conjunction with the bidirectional reflectance distribution function (BRDF) defined by Nicodemus. Unfortunately, the BRDF does not describe polarization effects. In recent years, polarized descriptions of surface scattering have been developed, but the relationship between the BRDF and the polarized descriptions of surface scattering have not been published. The unpolarized description of surface scattering, which involves radiances and BRDFs, is extended to properly describe polarization effects. The concepts of radiance, irradiance, intensity, and radiant power are redefined as vector quantities. The intensity vectors are defined as conventional Stokes vectors and as the modified Stokes vectors adopted by Ishimaru, Ulaby, and others. The BRDF and directional reflectance matrices are defined and expressed in terms of the amplitude scattering matrix elements and in terms of the intensity scattering or phase matrix. The relationships between the unpolarized and polarized BRDFs and directional reflectances are discussed.

The four optimum rotation angles for a polarimeter consisting of a quarter-wave plate in conjunction with a linear polarizer are found. This is done by using the determinant and condition numbers of the system measurement matrix as objective functions in a minimization procedure. The four angles so found result in the polarimeter's estimate of the incident Stokes vector to have a minimum sensitivity with respect to fluctuations in the detected flux and errors in the angular position of the optical components constituting the polarimeter. Four optimal angles are presented. These four angles also retain a simplicity of form for the measurement matrix.

The four sets of two optimum rotation angles for a polarimeter consisting of a quarter-wave plate in conjunction with a linear polarizer, both of which are free to rotate, are determined. These angles are obtained by maximizing the determinant of the system measurement matrix. The determinant for this system is approximately twice the value of the determinant when only the quarter-wave plate is free to rotate. In addition, the condition numbers of the measurement matrix decrease with the additional consideration of a rotatable linear polarizer.

The liquid crystal polarimeter (LCP) is a low-voltage complete Stokes polarimeter and spectral analyzer designed for measuring solar vector magnetic fields. The polarimeter consists of polarization and spectral analyzer sections, each a stack of commercially available nematic and ferroelectric liquid crystals. Used in conjunction with a Lyot birefringent filter and 2 CCDs, the system provides an essentially simultaneous polarization-spectral measurement by modulating input and output ferroelectric liquid crystals in phase at up to 31 .5 kHz. Each measurement determines a single magnetic-field physical parameter unaffected by atmospheric seeing. The sequence of four Stokes parameters spectrally sampled in even and odd components in the solar line is obtained in successive reads of the CCDs with different settings of the nematic liquid crystals. The LCP provides solid state imaging of the vector magnetic flux, Doppler velocity, intensity, and equivalent width in a solar spectral line. Our differential method with 2 CCDs allows for automatic CCD gain and dark-current correction. The design provides a considerable simplification to previous magnetograph designs for greatly improved speed, sensitivity, and flexibility. Some of our tests of the liquid crystals and of the LCP are described.

A polarization transformer in combination with a polarization analyzer is well suited for the generation of any wanted polarization state. We describe the setup, calibration, and applications of an in-line fiber optic polarization detector (IPD) built with a fiber optic coupler of 99% coupling ratio. At the low power output port we use standard beamsplitters and polarizers to generate four different polarization dependent signals. For calibration, the polarization is measured at the high-power output port with an oft-line polarimeter (OPD). This enables the determination of the system matrix, which represents the relation between the polarization at the high-power port and the four signals at the low-power port. With this system matrix, a continuous and accurate determination of the polarization at the high-power output port is possible.

Hybrid correlators are composed of numerous nonideal electronic and optical components that, to one degree or another, limit performance through unintended transformations of signals. Many of these eftects show up as phase errors at a spatial light modulator (SLM) plane. The errors can be described as random variables, or as systematic offsets from the correct phases, as appropriate. Sources of systematic phase errors include quantizing circuits, incorrect or nonlinear amplifier gain, limited range phase modulators and residual phase modulation of amplitude-mostly SLMs. Random phase errors arise from electronic noise and fabrication variations of SLMs. Several systematic and random filter plane errors are related through a single parameter that describes the amount of phase mismatch. A model of peak-to-noise ratio (PNR) is also presented that describes the combined effects of random and systematic errors. This expression contains the products of two functions, one that depends only on systematic, the other on random, phase mismatch. PNR is also a function of the number of pixels in the filter plane modulator and a normalized moment of the amplitude of the image spectrum. The model is useful for developing phase error budgets for correlation systems.

The nondiffractive propagation of the ideal zero-order Bessel beam is explained in terms of both the geometrical imaging and the interference of spherical waves emitted from the ring source. The source shift with respect to the focal plane of the imaging system is simply related to the divergence of the produced beam. The intensity distribution of the ideal Bessel beam in the focal region is examined for an aberration-free lens of finite aperture. Both the resolution gain at the focal plane and the position of the axial intensity maximum are investigated in dependence on the truncation of the input Bessel beam.

Light coupling to planar guided-wave optical circuits by means of directional coupling between D-fiber and buried square waveguide is indicated as a viable means of reducing alignment tolerances in fiber-pigtailing procedure of integrated optical devices. The geometry studied consists of a circular core fiber vertically coupled to a buried square waveguide. An accurate analysis by a vectorial formulation of the finite element method is presented. The structure is analyzed for generic cladding and core configurations. The dependence of power transfer efficiency from waveguide size and refractive index is investigated. The influence of the vertical separation between D-fiber and square waveguide on the overall coupled power is also analyzed. It is shown that because of mode mismatch at the input and output sections of the coupler between the field distributions of isolated guides and coupled guides, the power transfer is limited by radiation losses. By appropriately sizing the coupler and by choosing suitable refractive index values, the power transfer efficiency from the D-fiber to the square waveguide can approach 100%.

We describe new methods to obtain nonorthogonal Gabor expansions of discrete and finite signals and reconstruction of signals from regularly sampled short time Fourier transform (STFT) values by series expansions. By this we understand the expansion of a signal of a given length n into a (finite) series of coherent building blocks, obtained from a Gabor atom through discrete time- and frequency-shift operators. Although bump-type atoms are natural candidates, the approach is not restricted to such building blocks. Also the set of time- and frequency-shift operators does not have to be a (product) lattice, but just an ordinary (additive) subgroup of the time/frequency plane, which is naturally identified with the 2-D n x n cyclic group. In contrast, other nonseparable subgroups turn out to be more interesting for our task: the efficient determination of a suitable set of coefficients for the coherent expansion. It is sufficient to determine the so-called dual Gabor atom. The existence and basic properties of this dual atom are well known in the case of lattice groups. It is shown that this is true for general groups. But more importantly, we demonstrate that the conjugate gradient method reduces the computational complexity drastically.

Fractal coding of digital images offers many promising qualities. The coding process, however, suffers from the long search time of the domain block pool. We obtain mathematical results on the distance measure used in the search. Then we derive an incremental procedure to bound the domain block pixels. We arrange the domain blocks in a tree structure and utilize the procedure to direct the search. We show that this method speeds up the coding process by up to 50 times, without noticeable loss of image quality. Our procedure works in conjunction with other methods such as block classification

Although much work has been done toward developing lossless algorithms for compressing image data, most techniques reported have been for two-tone or gray-scale images. It is generally accepted that a color image can be easily encoded by using a gray-scale compression technique on each of the three (say, RGB) color planes. Such an approach, however, fails to take into account the substantial correlations that are present between color planes. Although several lossy compression schemes that exploit such correlations have been reported in the literature, we are not aware of any such techniques for lossless compression. Because of the difference in goals, the best ways of exploiting redundancies for lossy and lossless compression can be, and usually are, very different. We propose and investigate a few lossless compression schemes for RGB color images. Both prediction schemes and error modeling schemes are presented that exploit interirame correlations. Implementation results on a test set of images yield significant improvements.

We present a new shape recognition algorithm for binary images based on the morphological approach. The standard algorithms based on the morphological hit-or-miss transform use block structure patterns, but in many practical situations, this may cause problems because the size of the object is unknown. In the proposed method, we match the corners of the object instead of the block structure pattern. Because most objects have different structure elements for the corners, our method gives a more reasonable approach and the size of the object plays a less significant role in our recognition algorithm than in the standard algorithms. Our method can be easily adapted to recognize the features of different types of objects.

New classes of nonimaging reflector designs, referred to as tailored edge-ray designs (TEDs), were recently developed as basic solutions for the problem of designing a reflector that achieves a specified distribution of radiation on the target. These designs yield exact solutions, even when the source is extended, i.e. , not small compared to the reflector size. A systematic exploration of these designs for the practical and challenging problem of producing uniform far-field irradiance for linear (2-D) configurations is presented. We establish the inherent, fundamental limitations on the dimensional and flux-map characteristics of these TEDs. We develop designs that are a significant improvement over conventional approaches in meeting the practical design goals commonly set by luminaire manufacturers. We also derive analytic simplifications in the relevant formulas that can save considerable time in design calculations.

The lattice vibrations of barium metaborate (β-BaB₂O₄) crystal are analyzed with the aid of space group theory. The β-BaB₂O₄ crystal belongs to space group C⁶3v (R3C). The vibration modes are classified by the method of the factor group of the space group. The results of infrared and Raman spectra are given.

Estimates are made of nodding requirements for a secondary mirror used for radiometry of satellites in the 8- to 12-μm band. The first portion of the analysis determines the fundamental nodding frequency based on atmospheric turbulence and wind measurements taken at the Air Force Maui Optical Station. The temporal power spectral density for sky background fluctuations shows that a 50-Hz frequency will satisfy 50-percentile wind and turbulence conditions. The required frequency for a maximum operating wind condition of 40 mph is above 100 Hz. In addition to the 50-Hz fundamental, the analysis indicates that at least one, and preferably two, higher order harmonics of 150 and 250 Hz, respectively, are required to reconstruct a mirror drive waveform with sufficient duty cycle or integration time for background subtraction. The results are shown to be consistent with the performance of existing nodding systems.

Experimental measurements of polarized light scattered from a rough oxidized metal surface are presented. The metal is a heavily oxidized nickel alloy taken from tubes in a large steam reformer furnace. Many of the existing models for reflections off rough surfaces are tested on the data. A semiempirical model based on the approach of Torrance and Sparrow is developed and gives a good fit to the data. The model is computationally inexpensive and permits modeling of the reflection corrections in the radiation thermometry of reformer furnaces.

Pattern recognition theory is introduced to perform rough surface classification. The light intensity distribution scattered from a rough surface is defined as the pattern vector of the rough surface. Using the Karhunen-Loeve transformation, the pattern vector is transformed into a feature vector for classification. To achieve a maximum separability, a modified method is proposed. The feasibility and effectiveness of the proposed method is demonstrated by computer simulation results.

Optical analysis of rough single and double layers is performed by interpreting the spectral dependences of the measured coherent reflectance. Formulas for the coherent reflectance of these systems derived within the scalar theory of diffraction of light are used for this interpretation. Possibilities and limitations of the method utilized are illustrated using several concrete samples of both the rough single and double layers represented by models corresponding to fully correlated (identical), partially correlated, and fully uncorrelated boundaries. It is shown that the values of the optical parameters, the root-mean-square (rms) values of the heights of the boundary irregularities and the values of the cross-correlation coefficients of the boundaries characterizing the layered systems mentioned can be determined within the method described.

An optomechanical photonic switch that exploits the stationary property of the minimum deviation angle of a dispersive prism is described. The switch is based on an optical beam deflector consisting of an electric motor with hollow shaft. The tip of the motor is fitted with a dispersive prism and the deflected beam is focused onto pixels arranged around a circular scan track. It is shown that the proposed switch is, for all practical purposes, completely insensitive to mechanical wobble of the motor. Furthermore, the existing technology suggests that such a small-inertia motor with no external load may achieve speeds up to hundreds of thousands of revolutions per minute and beyond. We suggest one application of the switch as a write gate of a time slot interchanger in the time-division switching of pulse code modulation (PCM) codes. It is shown that the proposed switch can achieve speeds up to and exceeding hundreds of megabits per second.

Many studies on thermal processing of thin-film structures assume an incoherent thermal emission with an emissivity value that is constant or varies according to bulk properties. However, thermal radiation has a coherence length that varies with temperature. Thus, coherent thin-film interference affects the radiative properties of heterostructures when the wavelengths of radiation are of the same order of magnitude as the film thicknesses. For semiconducting and dielectric thin films on optically thick substrates, there are distinct trends in these microscale radiative effects. Numerical simulations of the temperature-dependent optical characteristics of multilayer thin-film structures were conducted to evaluate the thin-film interference effects. These results can be applied to thermal processes of thin-film structures where a spatial or temporal temperature distribution exists. An example of these effects is shown for radiative cooling of silicon-on-insulator wafers.

To explore the origin of chuck-related surface nonuniformities in thin films deposited from solutions, real-time observations of evaporative cooling effects during spin-coating of solvents are made using an IR switched-field-effect-transistor (FET) array camera. The evaporative cooling depends strongly on the volatility of the solvent being tested. For acetone (the most volatile solvent tested) the cooling eftect can be as large as 10°C when a silicon wafer is used as the substrate. Comparisons are made between wafer type and position on the substrate and sources of the temperature differences are discussed within the framework of the basic spin-coating paradigm. It is likely that these evaporative cooling effects play an important role in the development of chuck-related surface nonuniformities during spin coating; solvent systems may be selected to help optimize film uniformity. These aspects of solution engineering are also discussed.

An efficient method for tracking the attitude and translation of an object from a sequence of dense range images is demonstrated. The range data are sine coded and then Fourier transformed. By this process, planar surfaces in the image produce distinctive peaks in the Fourier transform spectrum. The position of a peak provides a direct measure of the normal of the plane. Tracking the positions of these peaks enables tracking the orientation of a known object. After computing and undoing the rotation, the translation is obtained by measuring the 3-D centroid of the segmented planar surfaces. All computations are closed form. The Fourier transform method is also used for segmentation. The integrative nature of the Fourier transform is very effective in attenuating the effect of noise and outliers. Results of tracking an object in a simulated range image sequence show high accuracy [0.2 deg in orientation and 0.2% root-mean-square (rms) error in translation with respect to the width of the object]. The system runs presently at 3 to 5 frames/s. The method promises real-time (video rate) performance with the addition of accelerator hardware for computing the Fourier transform. The approach is well suited for dynamic robotic vision applications.

A new method of real-time high-resolution imaging through the atmosphere is presented. This technique is based on knowledge of average atmospheric modulation transfer function (MTF) at the time the image is received. Atmospheric effects are modeled by a noisy spatial frequency filter including an average component described by the average atmospheric MTF and a noisy component modeled by the atmospheric point spread function's power spectral density. The noisy component represents random changes in the atmospheric MTF. Analytical results are accompanied by experimental image restoration examples, indicating significant image quality improvement based on knowledge of average atmospheric MTF, which includes both turbulence and aerosol MTF components. This method can be used to help overcome the jitter characteristics of turbulence, and is capable of yielding real-time image restoration with resolution limited essentially only by the hardware itself. Turbulence blur, aerosol blur, and contrast degradation are all corrected simultaneously, unlike adaptive optics, which corrects for turbulence only.

The performance of starting PtSi infrared cameras is characterized based on estimating their spatial frequency response. Applying a modified knife-edge technique, we arrive at an estimate of the edge spread function (ESF), which is used to obtain a profile through the center of the 2-D modulation transfer function (MTF). Using this technique, the complete system MTF in the horizontal and vertical direction is measured for various imaging systems. The influence of charge transfer efficiency (CTE) on the knife-edge measurement and resulting MTF is also modeled and discussed. An estimate of the OlE can actually be obtained from the shape of the ESF in the horizontal direction. In addition, we demonstrate that this technique can be used as a field measurement. By applying the technique at long range, the MTF of the atmosphere can be measured.

The amplitude transfer function for coherent imaging in the Fresnel approximation is derived. It is shown that this transfer function can solve problems in Fresnel diffraction that the more usual Fraunhofer approximation cannot. Because of its simple form, it allows for the formal solution of the aperture specification problem in diffractive optics by giving the complex optics transmission function in terms of a given object plane amplitude distribution and a desired image plane amplitude distribution. Two examples of this use are presented. Finally, the generalization of this transfer function to imaging in partially coherent and incoherent light follows easily.

A new method is presented to solve a zoom system in which the lenses are divided into two combined units, and each combined unit is defined as an optical component. It is shown that most zoom systems can be considered as two-component systems and can be solved using principal plane techniques of optical component, and the first-order zoom system design is thus made easier. The theory with some examples are described.

This PDF contains the communication "Gaussian random number generation by differential detection of speckles."

This PDF file contains a Comment on the paper "Etalon effects in laser mirrors," and a response from the authors.

This PDF file contains the editorial “Book Rvw: Optical Communications: Second Edition," by Robert M. Gagliardi and Sherman Karp for OE Vol. 34 Issue 06

This PDF file contains the editorial “Book Rvw: Adapted Wavelet Analysis from Theory to Software," by Mladen Victor Wickerhauser for OE Vol. 34 Issue 06