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Ultraviolet decontamination of personal protective equipment, particularly masks, is important in situations where mask reuse is practiced. To assist in the development of UV-C decontamination chambers, we have constructed ray tracing models in Zemax OpticStudio v20.1 for two distinct geometries, namely, a rectangular cabinet and a cylindrical can. These models provide irradiance distributions that can be used for comparison with experiment, as well as to predict local irradiance variation over the surface of a mask. In this paper we describe the model details, including: (1) a mask object in CAD format; (2) our assumptions for modeling surface properties; (3) the use of polygon object detectors for local irradiance analysis; and (4) experimental results that compare favorably to the simulations.

We present evidence-based design principles for three different UV-C based decontamination systems for N95 filtering facepiece respirators (FFRs) within the context of the SARS-CoV-2 outbreak of 2019–2020. The approaches used here were created with consideration for the needs of low- and middle-income countries (LMICs) and other under-resourced facilities. As such, a particular emphasis is placed on providing cost-effective solutions that can be implemented in short order using generally available components and subsystems. We discuss three optical designs for decontamination chambers, describe experiments verifying design parameters, validate the efficacy of the decontamination for two commonly used N95 FFRs (3M, #1860 and Gerson #1730), and run mechanical and filtration tests that support FFR reuse for at least five decontamination cycles.

We propose a technique for data detection in a two-dimensional page-access optical memory. The technique combines sequence detection by the use of the Viterbi algorithm with decision feedback to improve the bit-error-rate performance in a system corrupted by intersymbol interference. It has an advantage in that it can be operated on a row-by-row basis as data are output from the optical detector. Use of the proposed scheme might ease the design tolerances of the optical components or permit the use of large data pages.

We discuss wavelength selection for true-color holography by investigating the sampling nature of the holographic process. During holographic recording the chosen wavelengths point sample the surfacereflectance functions of the objects in a scene. To understand the effect of this sampling on color perception, we study the tristimulus values of points in the reconstructed hologram. The sampling results in the holographic process being mathematically equivalent to integral approximations for the tristimulus integrals. By selecting efficient approximations, we infer wavelengths to use in color holography. Our analysis not only suggests wavelengths for the usual three-color holography but also suggests the use of four or more wavelengths to improve color reproduction in holography.

Two-dimensional velocity or displacement fields that are recorded as double-exposure speckle patterns may be measured with an anamorphic optical processor. The anamorphic optical processor measures one component of the velocity or displacement throughout a linear region of the double-exposure speckle pattern. The signal in the output plane of such a processor is a fringe pattern. An analysis to predict fringe modulation based on Fourier optics and the statistics of speckle patterns is developed. The analysis specifies the effects of both the speckle-recording optics and the anamorphic optical processor on the fringe modulation. The observed loss of modulation when the velocity or displacement component perpendicular to the measured component is increased is also described. Measurements of fringe modulations that are produced by anamorphic optical processors with and without increased tolerance to the perpendicular velocity component are compared to results of the analysis. Fringe modulation versus relative exposure in the double-exposure speckle pattern are also measured and compared to the results of this analysis. An anamorphic processor that reduces the time for digital processing of the fringe patterns by a factor of N (typically 128, 256, or 512) relative to the two-dimensional Fourier transform optical processor (with identical spatial resolution) is demonstrated.

We present a practical real-time optical pre-processor intended to enhance small defects in a smooth surface. The heart of the system is a photorefractive BSO phase conjugate mirror which reflects only the low intensity features of the object’s optical Fourier Transform. By adjusting the beam ratios so that only the low intensity, high spatial frequency image components are phase conjugated and inverse transformed, an image consisting of just the defects is produced. To our knowledge, this is the first use of this technique on opaque and non-periodic objects. We present experimental data showing enhancement of defects smaller than 0.2 μm.

This paper addresses the problem of visualizing 3-D scalar data, initially represented as an ordered set of digital images stacked parallel to each other. An observer’s ability to perceive the geometry of the structures in these data fields depends on the methods of reconstructing and displaying 3-D representations. We describe three computer-based visualization methods that share the common goal of displaying the interior structures of 3-D data, and we present the results of applying these methods to a set of fluid-flow data. Interactive peeling of smooth opaque contour surfaces is the best of the three methods: it gives excellent perception cues.

The geometrical design characteristics of multiple-image holograms are evaluated. A figure of merit expressing these characteristics as a function of the hologram diameter and the distance between the hologram and the image plane is developed. This value is then used to compare two designs which are capable of forming several hundred interconnections. The results indicate that these connections can be formed between points on the substrate separated by 2-3 cm provided that the holograms are separated from the substrate plane by 0.5-1 cm. Each hologram design is experimentally demonstrated in bleached photographic emulsions.

Three-dimensional optical data storage is demonstrated in an initially homogenous volume by first recording a reflection grating in a holographic photopolymer. This causes the entire volume to be weakly reflecting to a confocal read/write head. Superposition of two or three such gratings with slightly different k-vectors creates a track and layer structure that specialized servo detection optics can use to lock the focus to these deeply-buried tracks. Writing is accomplished by locally modifying the reflectivity of the preexisting hologram. This modification can take the form of ablation, inelastic deformation via heating at the focus, or erasure via linear or two-photon continued polymerization in the previously unexposed fringes of the hologram. Storage by each method is demonstrated with up to eight data layers separated by as little as 12 microns.

Micrometer-sized reflection holograms can be written into a rapidly rotating homogeneous photopolymer disk at the focus of a high-numerical-aperture beam and its retroreflection to implement high-capacity multilayer digital data storage. This retroreflection is generated by an optical system with positive unity magnification to ensure passive alignment of the counterpropagating beam. Analysis reveals that the storage capacity and transfer rate of this bit-based holographic storage system compare favorably with traditional page-based systems but at a fraction of the system complexity and cost. The analysis is experimentally validated at 532 nm by writing and reading 12 layers of microholograms in a 125-microm photopolymer disk continuously rotating at 3600 rpm. The experimental results predict a capacity limit of 140 Gbytes in a millimeter-thick disk or over 1 Tbyte with the wavelength and numerical aperture of Blu-Ray.

We describe the design and implementation of a high-data-rate high-capacity digital holographic storage disk system. Various system design trade-offs that affect density and data-rate performance are described and analyzed. In the demonstration system that we describe, high-density holographic recording is achieved by use of high-resolution short-focal-length optics and correlation shift multiplexing in photopolymer disk media. Holographic channel decoding at a 1-Gbit/s data rate is performed by custom-built electronic hardware. A benchmark sustained optical data-transfer rate of 10 Gbits/s has been successfully demonstrated.

Unwanted erasure during readout of holographic data can be reduced or eliminated by use of a different wavelength for reading than that which was used for writing. To prevent distortion and Bragg mismatch that would be unacceptable for digital data storage, one can format data to account for the wavelength difference. Techniques to format data and the results of this formatting are presented. Varying the formatting parameters is investigated to optimize diffraction efficiency.

An encryption method and apparatus for holographic data storage are disclosed. In a system using orthogonal phase-code multiplexing, data is encrypted by modulating the reference beam using an encryption key K represented by a unitary operator. In practice, the encryption key K corresponds to a diffuser or other phase-modulating element placed in the reference beam path, or to shuffling the correspondence between the codes of an orthogonal phase function and the corresponding pixels of a phase spatial light modulator. Because of the lack of Bragg selectivity in the vertical direction, the phase functions used for phase-code multiplexing are preferably one dimensional. Such phase functions can be one-dimensional Walsh functions. The encryption method preserves the orthogonality of reference beams, and thus does not lead to a degradation in crosstalk performance.

We have built an adaptive system capable of detecting submicrometer defects in periodic structures by using real-time holography in photorefractive crystals. We summarize the design and optimization of the defect-enhancement system. We present representative results of 0.2- to 0.5-µm diameter defect detection on two different periodic substrates: chrome-on-glass masks and patterned silicon wafers. On patterned silicon we detect 94% of the 0.5-µm diameter defects with three false positives, while inspecting an area greater than 1 mm(2) in 20 s or less. The throughput on the glass masks is somewhat less. To the best of our knowledge, these defects have an area 100 times smaller than those previously detected with any real-time holographic technique.

Growth-induced striations in photorefractive media constitute phase gratings that scatter transmitted light and therefore degrade the quality of reconstructed images in holographic applications. A simple angular multiplexed holographic memory arrangement in a striated strontium barium niobate sample is considered. For forward-propagating reconstruction the striations distort the readout images and introduce ghost images. For counterpropagating readout, inhomogeneous image reconstruction and interimage cross talk can occur. We investigate these effects experimentally for different reconstruction methods and demonstrate the cross talk and the ghost images with a simple model based on coupled-wave theory. Readout with a counterpropagating plane wave eliminates the ghost images and the distortions but suffers degradation from cross talk and inhomogeneous image intensity. Only reconstruction with a phase conjugate of the transmitted reference beam eliminates cross talk and distortions. The model indicates that negligible material dispersion is a necessary requirement for high-quality phaseconjugation readout.

The number of holograms that can be linearly superimposed on one photographic plate has two fundamental limits; one is the finite extent of the characteristic amplitude transmittance vs energy-of-exposure (Ta − E) film curve, and the other is holographic reciprocity law failure [ K. M. Johnson L. Hesselink J. W. Goodman , Appl. Opt.23, 218 ( 1984)], the chronological decrease in brightness of reconstructed images in a multiple-exposure hologram. In this paper a multistep hologram, called the multiple multiple-exposure hologram, is presented which increases the number of holograms that can be linearly superimposed on one photographic plate and reconstructs images of equal brightness. The brightness of the reconstructed images in the final display hologram is a function of the reference-to-object beam ratio K in the intermediate and final steps of the multiple multiple-exposure hologram. By choosing different values for K in each step of this technique, a cross section can be displayed with the same diffraction efficiency in the initial multiple-exposure holograms and the final multiple multiple-exposure hologram. The trade-off between the maximum number of holograms that can be linearly superimposed on one photographic plate and the signal-to-noise ratio in the final display hologram is also discussed.

This paper is concerned with the propagation of laser light through a slab of a randomly varying medium. A theoretical analysis is presented which relates the spectrum of the recorded-intensity field some distance downstream of the medium to the spectrum of the index-of-refraction field. For a homogeneous and isotropic random field, the 3-D spectrum of the medium is obtained from the 2-D spectrum of the photograph by dividing each component of the spectrum by the frequency raised to the fourth power. Free-space propagation outside the random medium is accounted for by a scaling factor. Experimental results are presented which support the theoretical analysis. The nonintrusive diagnostic technique presented here is applicable to photographs which contain partially developed caustic networks.

In this paper, a tomographic procedure for reconstructing the density field around a helicopter rotor blade tip from remote optical line-of-sight measurements is discussed. Numerical model studies have been carried out to investigate the influence of the number of available views, limited width viewing, and ray bending on the reconstruction. Performance is measured in terms of the mean-square error. It is found that very good reconstructions can be obtained using only a small number of views even when the width of view is smaller than the spatial extent of the object. An iterative procedure is used to correct for ray bending due to refraction associated with the sharp density gradients (shocks).

An imaging system is proposed as an alternative to metallized connections between integrated circuits. Power requirements for metallized interconnects and electrooptic links are compared. A holographic optical element is considered as the imaging device. Several experimental systems have been constructed which have visible LEDs as the transmitters and PIN photodiodes as the receivers. Signals are evaluated at different source–detector separations. Multiple exposure holograms are used as a means of optical fan out allowing one source to simultaneously address several receiver locations. Limitations of this technique are also discussed.

Previous authors have reported a falloff in diffraction efficiency of reconstructed images in multiple-exposure holograms. We call this phenomenon holographic reciprocity law failure. We propose an explanation for this phenomenon based on latent image formation in photographic materials and discuss a method for superimposing holograms that reconstruct images of equal brightness.

We demonstrate a technique by which components of an image moving with a given speed and direction may be selectively enhanced. By using the strong grating velocity sensitivity of the nonlinear photorefractive response, we show that a BSO crystal used in a schlieren imaging system may be used as a real-time velocity filter. The velocity selectivity, tunability and resolution constraints of this system are discussed in detail.

In this paper, we consider a two-wave mixing system using a photorefractive medium and compute the diffraction efficiency as a function of the writing beam ratios. In certain conditions, the diffraction efficiency is shown to be exactly proportional to the inverse of the object beam intensity. Experimental results, obtained using a Bi12GeO20 crystal, are compared to the theoretical expression. In particular, we investigate the dependence of the range of beam ratios over which inversion occurs on the experimental parameters of total writing beam intensity and applied electric field. Results of performing inversion of gray-scale objects using a degenerate four-wave mixing setup are shown.

Optical computer assisted tomographic (OCAT) reconstruction of a three-dimensional unsteady object requires simultaneous acquisition of many line-of-sight measurements (projections). A projection represents a measurement of absorption or index-of-refraction along the pathlength. To acquire one projection a source, often a laser, is used in conjunction with beam steering and recording elements; all necessary projections can be obtained by either rotating the object, by rotating the data acquisition apparatus or alternatively by replicating the system required for making one projection. All these approaches have been investigated in the past for the purpose of making, for instance, measurements of quasi-stationary objects (Ref 1) or time-averaged measurements of complicated turbulent flows (Ref 2). Replication often leads to cumbersome and expensive optical systems and the lack of availability of a simple fast data acquisition system has impeded wide spread use of optical tomography in fluid mechanics research.

A coupled wave model for two multiplexed reflection holograms recorded in a volume material is presented. Both simultaneously and sequentially formed gratings are evaluated. The effects of a strong intermodulation grating, the thickness change with emulsion processing, and the construction geometry on the desired diffraction orders are investigated over a range of reconstruction angles. The model results are compared with experimental data from holograms formed in bleached photographic emulsions.