bluuebunny/crossref_metadata_2025 huggingface dataset:
New approaches to holographic video
Authors: St-Hilaire Pierre , Lucente Mark , Wadlington John , Arias Derrick , Benton Stephen A.
Published: February 2023

The MIT holographic video system has displayed color holograms of excellent quality but is limited in its present implementation to images of a few tens of millimeters on a side. This limitation is a consequence of using a polygonal mirror as a horizontal scanning element. It can be demonstrated that the diameter of this scanning polygon scales linearly with the display’s horizontal size, leading rapidly to impractical polygon dimensions. Replacing the polygon by a galvanometric scanner introduces a different set of design constraints since the mirror dimensions scale with the image size. Because the scan rate of a galvanometric scanner goes down as the mirror size is increased, we are faced with unpractically low scan rates for images larger than 5 cm. A solution to this problem is to use an array of small galvanometric scanners. Such low inertia scanners offer an acceptable linear response up to a few hundred hertz but can actuate only small mirrors. The mathematical optics of the MIT display, however, allow for the operation of an arbitrary number of scanning elements working in parallel. This makes possible the display of large images without the use of bulky electro-mechanical components. After a brief description of the issues involved we will describe the latest results obtained by using this novel approach and will show how it could lead in theory to even larger displays.
Compact, wide field-of-regard beam steering optics comprising two-lens modules
Authors: Gierloff J. J. , Dall’era A. , Johnson R. B. , Feng C.
Published: February 2023

A variety of applications exist for a compact, wide field-of-regard optical system that allows beam steering and serves as an optical window and the system aperture stop. Recently, a study was performed to investigate the possibility of designing and fabricating a small array of miniature lenses that would allow a detector array with an instantaneous field of view of 1.5° to be swept through an angle of up to 60° by simple movement of an element in the optical system. It was found that such designs with essentially diffraction-limited performance can be formulated for the 3.1–4.1 µm spectrum by using afocal modules comprising only two silicon lenses, where the second lens moves with respect to the first lens to provide the beam steering action. The spatial path followed by the second lens can be made to be circular with almost no degradation in performance, thereby minimizing the complexity of the scan mechanism. Results are presented that demonstrate the robust nature of the beam steering optics to large thermal gradients. Specific designs for one-dimensional and two-dimensional scanning systems with multiple lens modules are be discussed.
Aberration theory in the design of rugged optical systems
Authors: Reardon P. J. , Chipman R. A.
Published: February 2023

Optical designs for hypersonic vehicles and other hostile environments are discussed, with emphasis placed on the aberrations of alternate design concepts. By using the conceptual framework of the lens design continuum, the aberrations of specific regions of lens design space are explored. First, the lens design continuum is defined as a set of orthogonal coordinate axes. These axes are defined by surface curvatures, thicknesses, and material indices and also by numerical aperture, field of view, and entrance pupil location. Lens systems, defined as lens vectors, are then rotated through lens design space by using well defined lens transformation matrices. By explicitly defining the function and resulting lens quality for a specific lens transformation, they can then be arbitrarily applied to a given lens vector, yielding known results. These transformations allow generalities of the lens design continuum to be explicitly defined. The symmetries and characteristics of the lens design continuum are explored.
Zero-phonon lines in the luminescence spectra of ZnWO4 and electron–phonon interactions
Authors: Wang H. , Medina F. D. , Zhou Y. D.
Published: February 2023

The photoluminescence spectra of ZnWO4 in the near infrared region were obtained in the temperature range from 10 to 400 K. Zero-phonon lines and phonon replicas were observed. The temperature dependences of the shapes, widths, positions, and intensities of the zero-phonon lines in the infrared emission band of ZnWO4 single crystals were investigated experimentally. The results obtained are discussed in terms of the theory of electron–phonon interactions in impurity crystals. Anharmonic effects of the crystal vibrations are discussed.
Spectroscopy of dressed-atom states
Authors: Gauthier D. J. , Sukow D. W. , Concannon H.
Published: February 2023

Gain arising from the interaction of intense laser fields and atoms has attracted recent attention because it has been found, for example, that two-photon lasing1 and lasing without inversion2 occurs in these systems. Physical and intuitive models of these interactions can be developed by using the dressed-atom states, which, unfortunately, tend to be difficult to detect directly with high precision. We will report on a new modulation spectroscopy for the quantum limited detection of gain in dressed-atom systems. The spectroscopy involves weak modulation of the dressed-state splitting and lockin detection of the intensity of the probing beam. It differs from classic frequency-modulation spectroscopies in that the probe beam is not modulated before it interacts with the sample of strongly driven atoms and hence does not suffer from the effects of residual amplitude modulation.
Higher order structure functions and their effects on remote sensors
Authors: Walters Donald L.
Published: February 2023

Structure functions used in atmospheric optics remove means and regularize turbulence integrals. Recently, Yaglom extended this approach to generalized, self-similar processes with stationary increments of order n. We have applied this technique to a single microthermal probe carried by a balloon system. The higher order structure functions have completely removed non-turbulent low order trends in the data and provide a consistent set of higher order structure parameters along non-stationary, non-isotropic atmospheric paths. Other applications of this approach are possible.
Investigation of transient nonlinear response of PLZT thin films
Authors: Bao C. , Diels J.-C. , Wu A. Y.
Published: February 2023

We studied the second harmonic of 1.06μm in 28/0/100 PLZT thin film under the influence of a picosecond electric field. The field is produced by a photoconductive switch. The switch consists of a coplanar stripline circuit on a semiconductive substrates. The circuit includes a narrow central electrode that is sandwiched between two conductive surfaces. The central electrode and one of the conductive surfaces are at high potential. When a 530 nm picosecond pulse pumps the switch, an electrical pulse is produced and creates as it propagates along the transmission line, a field between the central electrode and the electrode originally at high potential. This electrical field is used to induce the second harmonic generation (SHG) in PLZT film. We press a sapphire plate with a PLZT film on the top of the circuit and direct a probe beam (a picosecond pulse at 1060 nm) onto the sample.
Thin-film design using incremental layer optimization
Authors: Southwell William H.
Published: February 2023

One approach to the thin-film synthesis problem is to search for the best index profile, be it continuous gradient index or discrete multilayer, for a given optical thickness and index range. This formulation is sufficiently general to include a global optimum solution and is also practical now that gradient-index deposition methods have been demonstrated. One approach for finding such solutions is a method (first introduced by Snedaker in the 1982 OSA Annual Meeting) that divides the total thickness into many incremental layers and successively finds the optimum index within limits for each sublayer. We have successfully used this approach and have expanded on it in various ways to obtain nearly equivalent configurations that are more favorable for fabrication. It turns out that for many problems the solution is discrete multilayers at the low and high index limits. Solutions to difficult problems often yield new insights for standard approaches.
Novel nonclassical effects in the homodyne detection of squeezed light
Authors: Dodson Arlis , Vyas Reeta
Published: February 2023

Nonclassical effects exhibited by the homodyned field when light from an optical parametric oscillator (OPO) is mixed with coherent light from a local oscillator are discussed. Calculations are carried out exactly without making the strong local oscillator approximation. It is found that, depending upon the local oscillator phase and the parameters characterizing the light from the OPO, the second order intensity correlation function of the superposed field violates various classical inequalities g(2)(0) ≥ 1, g(2)(0) ≥g(2)(τ), and |g(2)(0) –1| ≥ | g(2)(τ)–1|. Thus we can see sub-Poissonian or super-Poissonian statistics and bunching or antibunching. We express the fields at the beam splitter in terms of independent real Gaussian stochastic processes with coherent component. Using these properties of the dynamical field variables, we derive analytic expressions for quantities directly measurable in photon counting experiments. It is found that the waiting time distribution shows two extrema at nonzero times. The second order intensity correlation function is found to vanish at nonzero time in violation of a classical inequality.
Gain-switched GaAs vertical-cavity surface-emitting lasers
Authors: Wiesenfeld J. M. , Hasnain G. , Damen T. C. , Shah J. , Wynn J. D. , Leibenguth R. E. , Wang Y. H. , Cho A. Y.
Published: February 2023

The production of ultrashort optical pulses from GaAs vertical-cavity surface-emitting lasers (VCSELs) has been demonstrated by electrical and optical gain switching. The monolithically grown devices have four quantum wells in the active region, and have dimensions and mirror reflectivities (distributed Bragg reflector stacks) optimized for cw operation under current injection. Pulses as short as 24 ps were produced by electrical gain switching and optical gain switching. The pulse durations were determined by the photon lifetime of the VCSEL, whose value is constrained by the requirements for cw operation under current injection. Thus, there are design tradeoffs for VCSELs between short pulse production versus efficient cw electrical operation. Measurements of the optical spectra show the time-bandwidth product can be as small as 0.6, suggesting very small chirp for a gain-switched laser. This is a consequence of the small thickness of the active region of the VCSEL. Also, for lasers operating at different wavelengths, there is an increase in pulse duration as the wavelength increases, which results from band-filling effects.
Diffraction-coupled two-dimensional arrays of surface-emitting lasers
Authors: Dziura T. G. , Wang S. C.
Published: February 2023

We have studied the operation of 2D arrays of vertical-cavity surface-emitting lasers (SELs) in which interelement coherence is maintained via diffraction coupling. SEL subcavities with mirrors M1 and M2 are phased locked by reflecting the output of M2 back into the array with a third mirror M3, with a round-trip separation from the array of either one-quarter or one Talbot distance. The threshold gain depends on the array fill factor and the particular array mode. For quarter-Talbot cavities the lowest order supermode, which has a single-lobed far field, has the lowest threshold gain for a wide range of fill factors. For large fill factors the threshold gain is low but the supermode gain discrimination is poor. For Talbot cavities our calculation includes the coupling from all neighbors (not just the nearest neighbor), and we find that independent of array size there are four supermodes that are effectively degenerate and that have the lowest threshold gain. All but the "in-phase" supermode can be discriminated against by selective reflection with the mirror M3. The optimum reflectivity for the mirror M2 is simply the inverse square magnitude of the coupling matrix eigenvalue.
Ultrashort light pulses in confocal imaging systems
Authors: Kempe M. , Rudolph W.
Published: February 2023

Tight focusing of ultrashort light pulses is very sensitive because of small amounts of chromatic aberration present in the optical system. This has to be considered if imaging with high spatial and temporal resolution is required. Introducing the concept of time-dependent amplitude point spread functions of lenses illuminated by a pulse of given amplitude spectrum, we can describe the imaging process using Fourier-optical treatment. We show that in a confocal syntem (e.g., a laser scanning microscope) the temporal resolution is determined by the pulse width of the incident pulse if a suitable annular objective pupil and chirped pulses are used, even if the objective shows chromatic aberration. The spatial resolution in discussed in terms of the time-averaged point spread function (PSF) as well as in terms of the optical transfer function (OTF). The OTF shows clearly the influence of chromatic and spherical aberration and defocusing on the imaging process. We analyze this with the aim of obtaining high spatial and temporal resolution simultaneously. Applications of such a confocal system are suggested.
Sagnac spectroscopy
Authors: Diels Jean-Claude , Diddams Scott A.
Published: February 2023

In a passively mode-locked femtosecond ring dye laser the two counterpropagating pulses have a relative frequency difference Av that can be adjusted from a few hertz to megahertz by rotation of the cavity. These opposing pairs of pulses can thus be used to establish coherence between sublevels of a A transition in a resonant vapor. Sagnac spectroscopy is the distortion of the (previously linear) Sagnac response of the laser when such an atomic vapor (Sm) is inserted in the cavity. Even though the bandwidth of this unstabilized laser is of the order of 1013 Hz, spectroscopic measurements can be performed with 10 Hz accuracy. Applications include magnetic field measurement, lasing without inversion, and giant index of refraction.
Anisotropic light-induced scattering and “position dispersion” in KNbO3:Fe crystal
Authors: Song Q. Wang , Banerjee Partha , Zhang Chun-Ping , Talbot Peter
Published: February 2023

The light-induced scattering in photorefractive crystals has been investigated widely by many researchers because it has important effects on photorefractive holograms, phase conjugation, etc. The characteristics of the pattern of the light-induced scattering depend on polarization and orientation of the illumination beam relative to the crystallographic axes of the crystal. Most studies of the light-induced scattering to date were performed with LiNbO3:Fe, LiTaO3, and BaTiO3 crystals at fixed distances between focusing lenses and samples.[1,2,3] KNbO3 is an important crystal used in two-wave mixing, phase conjugation, and dynamic holography. This paper presents the features of light-induced scattering and "position dispersion" of KNbO3:Fe crystal. The anisotropic scattering from the KNbO3:Fe crystal is shown to be dominated by light-induced lensing.
Theoretical and experimental results on beam fanning in LiNbO3
Authors: Banerjee Partha P. , Liu Jaw-Jueh , Song Q. Wang
Published: February 2023

Using a linearized form of the Kukhtarev equations, we study beam fanning in LiNbO3 when a Gaussian beam is incident on the crystal in which no hologram has been previously stored. Both steady state and transient solutions are provided. The space charge field is calculated by numerically integrating the charge distribution, which can be found in closed form in the spatial frequency domain. A split-step beam propagation method is thereafter used to analyze the propagation of incident Gaussians of arbitrary widths and radii of curvature through a "thick" sample of the material. Our results clearly show the transient buildup of beam fanning, which is also verified from experiment. In the case of Gaussian beam incidence on a previously stored grating in LiNbO3, beam fanning is observed in the transient state for both the diffracted and undiffracted light. Once again, this observation is corroborated with theoretical results.
Comparison between linearized and nonlinear theories of beam-fanning in BaTiO3
Authors: Banerjee Partha P. , Misra Raj M.
Published: February 2023

The nonlinear Kukhtarev equations can be decoupled in the steady state to yield a nonlinear differential equation for the space charge field. Under suitable approximations, we can express the induced refractive index profile explicitly in terms of the intensity profile, its spatial derivative, and the dark conductivity of the material. We can thus also derive a nonlinear extension of the paraxial wave equation for the optical field propagating through a photorefractive material. Using a thin sample approximation, we first study beam fanning in BaTiO3 and compare our results with existing ones derived from the linearized Kukhtarev equations. Analytically, the far-field profile may be expressed in terms of an Airy pattern and the Fourier transform of the input beam profile. Numerical results based on thick sample calculations are also provided.
Spatial and temporal integration in relation to the nonlinearity of light adaptation
Authors: MacLeod Donald I. A.
Published: February 2023

Stimuli that are spatially and/or temporally periodic, but too high in frequency to be subjectively resolvable, appear by definition uniform and steady. If processing is linear up to the stage at which resolution losses obliterate the stimulus modulation, this stimulus will match a uniform and steady stimulus of the same average luminance. The phenomena of difference-frequency gratings and contrast-modulation flicker are exceptions to this principle for unresolvable gratings in cone vision, and the direction of deviation from linearity suggests that a compressive or sensitivity-regulating nonlinearity precedes any neural spatial integration in the cone system. This nonlinearity is a dynamic one rather than an instantaneous compression. In the rod system, on the other hand, the spatially integrated signals are very nearly linear, even at saturating levels. In the short-wavelength cone system, compressive nonlinearity precedes both spatial and temporal integration, the latter being revealed in deviations from the Talbot-Plateau law under some conditions.
Facet heating in AlGaInP 670 nm double-heterojunction visible lasers
Authors: Tang Wade C. , Rosen Hal J.
Published: February 2023

Visible-laser diodes are attractive light sources in optical applications such as high-density optical storage devices and laser printers. The maximum output power attainable for AlGaInP lasers is currently not as high as that realized in AlGaAs lasers, but it is constantly improving. Studies carried out in AlGaAs (780-840 nm) lasers have indicated that high facet temperature plays an important role in facet degradation and catastrophic optical damage (COD). We will present data on the facet temperature measurements on 670 nm AlGaInP and 830 nm AlGaAs double-heterojunction lasers.
Optical neural network using competitive learning
Authors: Prévost Donald , Gagné Philippe , Arsenault Henri H.
Published: February 2023

Among the neural network models proposed, some of the most promising are those that use an optical correlator architecture. The fastest optical correlators are acousto-optical, but these are one-dimensional systems. Two-dimensional optical correlators can handle 2-D data and are particularly appropriate for the kinds of application for which optical neural nets are most promising, that is, recognition and classification of image formatted data. Because of the lack of suitable non-linear devices, present systems must use a combination of optics and electronics. Our hybrid system, which stores interconnect weights in a computer-generated hologram, and which includes a computer for thresholding and feedback, can implement a number of neural models including Hopfield, Hamming, adaptive resonance theory, and competitive learning. We report here on using this system for competitive learning applied to recognition of alphabetical characters.
The ideal observer: from images to objects
Authors: Kersten Daniel
Published: February 2023

The human visual system is remarkably good at making accurate and reliable interpretations of the world from incomplete or noisy retinal image data. It does this by exploiting implicit knowledge of the statistical regularities of both objects and images. By quantifying the statistical uncertainty inherent in a visual task, ideal observer models specify a limit on the best performance for that task. Comparisons of human and ideal performance, often made by measures of efficiency, can be used to quantify information utilization. Historically, this technique has been developed most fully in the context of visual sensitivity and the early coding of image information. Recently, the ideal observer has been extended to problems of image understanding. I will present an overview of the ideal observer in visual perception research with examples drawn from our work at early and late levels of visual processing. For example, at the image level, human discrimination efficiencies for fractal images are relatively best for fractal dimensions near those of natural image ensembles. At the object level, human classification efficiency for 3D shaded "wire" objects is high enough to exclude generalized 2D template models of recognition and indicates particularly efficient processing of mirror symmetric and coplanar 3D objects.
Analysis of SLM based dynamic holographic optical elements
Authors: Tam Eddy C. , Song Qiwang
Published: February 2023

The use of SLMs to display Fresnel lenses has been demonstrated in various papers.1-3 It has been shown that dynamic diffractive optical elements can be implemented with various types of light modulators. In this study, we investigate the nematic liquid crystal based spatial light modulators that can provide full range phase modulation. Even though the modulation speed is relatively slow compared with that of other SLMs, the high resolution, high space-band-width product, electrical address, and full range phase modulation property of a nematic liquid crystal SLM make it very attractive. We have performed some basic analysis on the quality and efficiency of these dynamic elements. The chromatic aberration of a hybrid refractive lens / dynamic diffractive lens combination is comparable to that of a low dispersive refractive lens. The phase assignment of the dynamic element is also computed with several optimum algorithms, and their performance and efficiency are discussed.
Diffraction of Gaussian beams by binary diffractive elements
Authors: Moharam M. G. , Pommet D. A.
Published: February 2023

Multi-level binary diffrac­tive optical elements are of increasing importance in an expanding variety of engineering applications. Virtually all previous work on the analysis and design of binary diffractive elements has been for diffraction of infinite plane waves rather than the practical case of finite bounded-profile beams. Only diffraction of Gaussian beams by thick holographic gratings has been previously investigated. In this work the diffraction of finite beams by multi-level binary gratings is analyzed in detail by using the rigorous coupled-wave approach. The analysis applies to any finite beam that is spatially slowly varying on the scale of the wavelength of light. Detailed diffraction characteristics for the important case of Gaussian beams are presented. The diffraction efficiency of these gratings and the profiles of the transmitted and diffracted beams are calculated as a function of the grating depth, grating spacing, light wavelength, and Gaussian beam waist. It is shown that if the beam waist is more than 10 times the grating period, the diffraction efficiency follows very closely to the plane-wave diffraction efficiency with no significant distortion of the profiles of the diffracted beams. The conditions for plane-wave-like diffraction behavior (with finite profile) are determined.
Building robustness into laser controlled chemistry through optical pulse shaping
Authors: Warren Warren S.
Published: February 2023

Applications of controlled laser fields (phase shifted pulse sequences, shaped laser pulses, coherent multiple-frequency irradiation) to prepare useful molecular states or alter molecular dynamics have been extensively explored both theoretically and experimentally over the last few years. To date, however, most of the experimental demonstrations have simply enhanced signals or modulated overall dissociation rates. We will survey this work (including our own contributions) and compare it with the theoretical promise of selective bond breaking, climbing anharmonic vibrational ladders, orienting molecules, suppressing relaxation, and altering reaction pathways. There are several important reasons for the gap between theory and experiment, but the most important is robustness—many proposed experiments are too sensitive to experimental inhomogeneities or imperfect knowledge of the molecular Hamiltonian to be implemented in the laboratory. Imposing robustness by frequency modulation provides an extremely robust approach to preparing population inversions, generating quantitative transfer between states, and modifying relaxation rates. Experiments with frequency swept laser pulses amply verify that even simple, poorly controlled waveforms can produce useful molecular states.
Multiple pulse femtosecond spectroscopy
Authors: Wiederrecht Gary P. , Wang Weining , Nelson Keith A.
Published: February 2023

Multiple femtosecond excitation pulses have been used recently for increased control over molecular motion. Several developments in this direction will be discussed. For excitation pulse sequences with many (i.e., more than two or three) pulses, computer control over the generation of the pulse sequence is essential. It is important to be able to analyze the molecular of material response to a given pulse sequence and generate a new, optimized pulse sequence on the spot. Multi-element liquid crystalline masks can be used to do this. The analysis of material responses and design of new masks could be done by the human experimenter or, ideally, by computer. Real-time, single-shot femtosecond data acquisition is also essential for condensed materials in which the goal of multiple-pulse excitation is controlled chemical or structural change. Much current effort is directed toward gas-phase samples in which a buildup of reaction product can be avoided by continuously flowing new material into the irradiated region. Most applications will involve crystals, polymers, and other nonflowable media. Multiple femtosecond probe pulses can be used to collect all the necessary temporal information after just one excitation event. In this manner fundamental and applied experiments can be conducted on condensed-phase materials.
Optically induced birefringence in lithium dimer as the result of resonant ultrafast pumping
Authors: Lin C. , Littman M. G. , Shen L. , Rabitz H. , Reitze D. , Weiner A. M. , Leaird D. E.
Published: February 2023

In this experiment, Li2 is excited from ground electronic state to the first excited state by 1 μJ, 75 s pulses from an amplified CPM laser at about 620 nm. The birefringence created by the pump pulses is measured at a delayed time by using a white-light-continuum probe (10 nm width, center at 770 nm and 800 nm). Unlike similar experiments, we are pumping in the resonance regime (the Rabi period here is 1-10 ps). This experiment is laying the groundwork for the use of shaped ultrafast pulses to develop a birefringence time history by design. We have computed a birefringence and dichroism signal based upon spectroscopy parameters. Most of the features have been confirmed experimentally. Experimentally, a birefringence step is observed after the initial pump pulse; this is due to a population transfer that results from the pumping process. Peaks that appear later are believed to be due to rotational coherences in the ground and first excited states.
Multiplexed holographic optical waveguide interconnects
Authors: Lin Freddie
Published: February 2023

Multiplexed volume holograms have been realized in optical single-mode waveguides. This technology can be applied to optical interconnects and has many other applications. In addition, devices or systems based on this technology can be realized in a compact and rugged configuration. This presentation provides this technology's basic components, experimental results, and potential uses. Volume holographic materials can be implanted in low-loss optical waveguides in such a way that numerous multiplexed gratings can be fabricated in the same volume. The number of multiplexed channels (related through the Bragg selectivity) and the grating storage (i.e., number of recorded gratings) are limited by the interaction length (T) between hologram and the guided waves rather than the physical thickness of the holographic emulsion (t), where T ≫ t. The combination of multiplexed waveguide grating coupler and multiplexed waveguide holograms has the ability to couple light from free space into several guided waves in the waveguide and then split each of these guided waves in arbitrary directions. This allows the compact packaging of opto-electronics chip planes and optical interconnect planes. Their applications include clock distribution networks, global interchip interconnects, and backplane optical interconnects.
Holographic integrated optical circuits
Authors: Grebel H. , Zhong W.
Published: February 2023

Optical interconnects and other passive integrated optical circuits require a selective distribution of light among several addresses. Bragg waveguides are optical guides in which the transverse confinement is maintained by a grating rather than a step or gradual change in the refractive index. A two dimensional holographic optical circuit is achieved by surface grooves. The grooves serve as confining structures as well as selective filters. In that respect, the circuit as a whole participates in the light channeling process similarly to holograms. Polymeric devices offer flexibility in synthesis and fabrication. If the concept of the distributed holographic element prevails, one can envision stamping holographic optical circuits in plastics. We have fabricated and analyzed polymeric, Bragg confined waveguides. The core of the waveguides was made by embedding conductive crystallites in a polymeric film (artificial dielectric layer). Patterning was made by photoablation of that layer, which also proved useful in terms of the spatial resolution needed. Other patterning techniques will be discussed too.
Monte Carlo and projection methods to correct motion artifacts in magnetic resonance imaging
Authors: Smith Warren E. , Riek Jonathan K. , Tekalp A. Murat
Published: February 2023

Motion artifacts arise in magnetic resonance (MR) imaging when the patient moves (e.g., respiratory, cardiac, involuntary) during data acquisition. These artifacts give rise to “ghosts” in the reconstructed image, which typically manifest themselves along the phase-encoding direction. A model is presented to predict these artifacts due to source motion perpendicular to the slice-selection plane of the acquisition system. A three-dimensional (3-D) source with nonuniform spin density is presumed, and an arbitrary slice-selection profile is permitted.
A Monte Carlo wave function method in quantum optics
Authors: Mølmer K. , Berg-Sørensen K. , Castin Y. , Dalibard J.
Published: February 2023

Very recently there have been a number of papers discussing the applicability of stochastic methods as an alternative to the usual treatment of master equations in quantum mechanics.1-5 In this paper we present a wave function approach including a stochastic element to study the evolution of a small system when it is coupled to a reservoir. We show how fluctuations and dissipation originate from quantum jumps occuring randomly during the time evolution of the system, and we present a physical interpretation of the procedure. We demonstrate how this treatment may replace a wide class of master equations, and its use in problems with a large number of states N is discussed. Since the density matrix has N ×N elements, where a wave function is determined by only N variables, there is a computational advantage in using the wave function procedure. This is illustrated by calculations on cooling atoms in a laser field.
High resolution 3-D soft x-ray holography
Authors: McNulty Ian
Published: February 2023

Recent advances in x-ray sources, optics, and detectors have opened the door to three-dimensional holographic microscopy. Soft x-ray holography is a promising tool for study of micrometer-sized biological objects in their natural state. X-ray holograms obtained to date resolve features smaller than 100 nm; however, they yield little depth information because of their relatively low numerical aperture. The effective aperture and depth resolution can be improved by combining holograms recorded at various illumination angles. We have undertaken an experimental demonstration of this technique at the NSLS undulator beamline X1A. By using coherent 3.2-nm x-radiation, Fourier transform holograms of microfabri-cated test objects were recorded at several orientations with a CCD camera. The holograms were numerically assembled and reconstructed. Preliminary results are presented.
Fresnel phase zone plates for hard x-ray applications
Authors: Lai B. , Yun W. B.
Published: February 2023

High quality hard x-ray phase zone plates have recently been demonstrated based on advances in fabrication methods. The capability of these phase zone plates to efficiently focus x-rays opens up many new applications. In particular, microimaging, microanalysis, microdiffraction, and micro-EXAFS have all been demonstrated with ≈2-μm spatial resolution. At the present time, the focal spot size is limited by demagnification of the source, but the results indicate that the diffraction-limited intrinsic resolution is less than 1 μm. These zone plates were fabricated with either a sputtering/slicing technique or an x-ray lithographic technique. Both types of zone plates were tested at 8 keV, and their optics properties (focusing efficiency, signal-to-background ratio) show differences that are consequences of the fabrication method.
Nonredundant recording and reconstruction for x-ray holography
Authors: Wang Zhijiang , Zhang Zhenquan
Published: February 2023

We analyze why high resolution images have not been obtained by previous x-ray holography. We think that the resolution limit of reconstructed images from Grabor and Leith holograms is restricted by the resolution limit of the recording media. The nonredundant recording method is suggested to match the information quantity of the recording films with that of the object. It is predicted that the resolution power of x-ray holography should reach its wavelength. The brightness of existing x-ray lasers is about 107 times that of the synchrotron radiation. But its pulse width is only 10−10 sec. The brightness must be enhanced significantly to compete with synchrotron radiation. The synchrotron radiation can provide a wavelength ranging from 10 Å to 1 Å. This is another advantage of the synchrotron radiation. We show that x-ray laser divergence angle can be remarkably compressed, even to its diffraction limits; therefore the brightness can be enhanced. For this purpose, the gain–length product of a single oscillator must be sufficiently high.
Optical materials for deep-UV lithography
Authors: Rothschild M.
Published: February 2023

The fabrication of microelectronic devices with 0.35-μm and 0.25-μm resolution is widely expected to be accomplished with photolithogaphic techniques employing deep-UV radiation, mainly 248-nm and 193-nm lasers. A major area of concern at these wavelengths is the availability of high-quality, radiation-insensitive refractive optical materials and thin films. In addition to meeting stringent requirements in areas such as index homogeneity, these materials must be transparent at the operating wavelength and must be unchanged by prolonged irradiation, in particular with pulsed lasers. This paper will review the phenomenology of radiation-induced defect formation in fused silica, crystalline fluorides, and multilayer dielectric coatings and will address the effects of material impurities and processing conditions. The useful lifetime of the optical components is determined by an interplay between the optical design, quantitative analysis of radiation- induced effects, photoresist sensitivity, and required wafer throughput. It is shown that with the appropriate choice of materials and design, photolithographic systems can be kept within performance specifications for over 10 years of full-time operation.
Improved GaAs metal–semiconductor–metal photodetector performance for epitaxial liftoff applications
Authors: Hargis M. C. , Brown J. S. , Jokerst N. M.
Published: February 2023

Deposition of thin film single crystal compound semiconductor devices onto host substrates such as silicon using epitaxial lift off (ELO) may enable low cost optical communication subassemblies. In order for ELO technology to be viable for communication systems, the detector performance must approach that of their on-wafer counterparts. The MSM detectors reported herein were designed to make use of the fact that both the front and back surfaces of the absorbing layer are accessible via use of a polyimide transfer diaphragm. To passivate the back surface of the MSM, a thin layer of titanium was evaporated and mesas were defined. The Ti/GaAs layer was then lifted off and placed on the transfer diaphragm. The device was inverted, Ti side down, onto the Si3N4/Si host, and the interdigitated finger contacts and pads were defined. We have seen an order of magnitude improvement in the dark current and modest improvement of the dc responsivity.
Integrated optical data storage: from components and devices to systems
Authors: Kurdi Bülent
Published: February 2023

Optical data storage, which is currently based on small discrete optical components, has already established a place for itself in the computer data storage hierarchy. Optical storage offers high storage density, removability, and archival readonly and read/write functionality. It is in the area of read/write applications where comparable performance to magnetic data storage is expected from magneto-optical data storage systems. Integrated optics technology offers a reduction of optical head cost, size, mass, manufacturing complexity, and critical alignment tolerances by means of migration from the assembly of miniature but discrete optical components to planar-processed, self-aligned integrated optical elements. After a brief description of a generic discrete component magnetooptical head, recent developments in the area of integrated optical head concepts will be reviewed. Antiresonant reflecting optical waveguide (ARROW) structures and a crossed-grating structure for performing magneto-optical (MO) polarization detection will be presented. The issues of waveguide and grating fabrication, efficient waveguide and detector coupling, and packaging and integration challenges will be discussed.
Demonstration of integrated optical serial-to-parallel converter for high data rate communications
Authors: Tan Ronson , Verber Carl M.
Published: February 2023

We have demonstrated an integrated- optical serial-to-parallel converter based on surface-emitting second harmonic generation. The SHG is produced when two counter-propagating waves overlap inside a nonlinear 1 -μm-thick multilayer Al0.9Ga0.1 As/Al0.7Ga0.3As waveguide. As a proof of concept, we input two 2-ps 1,32-μm pulses into the waveguide. Counter-propagation is achieved by Fresnel reflecting the input pulses at the waveguide–air interface or by coating one end of the waveguide to form a mirror. As expected, by controlling the pulse separation, we were able to control precisely where the pulses collide inside the waveguide and hence predict the positions at which the SHG will be emitted. The device can handle pulses spaced as close as 4 ps (0.2 mm in the waveguide), corresponding to a 250 Gb/s data rate. By placing a detector over each collision site, serial-to- parallel conversion can be accomplished. In addition, this device can also be used as a demultiplexor and for code-recognition in a code-division multiplexing scheme.
Dimer-dominated materials for upconversion applications
Authors: Cockroft Nigel J. , Murdoch Keith M.
Published: February 2023

In many laser materials ionic dopants adopt nominally random spatial distributions. Consequently, information on energy transfer processes must be convoluted by using models for the distribution of separations between ions. For energy transfer upconversion lasers such a distribution results in some dopant ions absorbing pump excitation but being too isolated to contribute to the upconversion process. CsCdBr3 is one of a class of novel materials that preferentially accommodate trivalent dopant ions in a single dimer configuration. The inter-ion separation of approximately 6 A enables efficient energy transfer and allows for the use of simple single-rate analysis models. This paper demonstrates the powerful use of CsCdBr3 as a tool to unravel energy transfer processes and illustrates its potential use as an efficient and versatile upconversion laser host. Single and dual laser pumped infrared to visible upconversion investigations on Er3+ ion dimers and heterogeneous Tm3+/Pr3+ ion dimers are reported. Mechanisms for the excitation wavelength controlled dominance of violet, green, or red Er3+ emission and the mechanism for blue Pr3+ emission after near- IR Tm3+ excitation are determined.
Photon avalanche upconversion in Tm: YLF
Authors: Case W. E. , Kueny A. W. , Koch M. E.
Published: February 2023

Avalanche excitation of thulium in YLF using laser light at 1.04 microns produces blue fluorescence and even stronger emissions of ultraviolet. The pump frequency is resonant only with a transition (3F4 → 3F2) from an excited state, not the ground state. If the pump intensity exceeds a certain threshold value, sustaining an absorber population becomes possible through crossrelaxation feedback from an upper state. We have previously reported1 on an avalanche model for Tm ions based on a presumed known two-ion cross-relaxation process (3H4, 3H6 → 3F4,3F4) and the assumption that Tm excitation is quasi-homogeneous in the pumped volume. Although the model correctly predicts important qualitative features of the avalanche, quantitative predictions are not in good agreement with experimental data. In this paper, we will report on several new directions taken in our theoretical modeling. Most successful is the idea of small clusters of Tm ions distinguishable in optical response from a more uniform background. The clusters account for both avalanche absorption of pump energy and upconversion.
Laser properties of Yb3+ in fluorapatite and other crystalline media
Authors: Payne S. A. , Krupke W. F. , DeLoach L. D. , Smith L. K. , Kway W. L. , Tassano J. B.
Published: February 2023

An extensive search algorithm has been exercised in order to identify Yb-doped laser crystals that possess the optical properties that are most amenable to pumping with InGaAs laser diode arrays. Numerous considerations arise in this context, including the magnitude of the absorption and emission cross sections and emission lifetimes, the nature of the 2F7/2 ground state crystal field splitting, the issues confronting the growth of high-quality samples, and the thermal, mechanical, and optical properties of the host medium. Yb-doped fluorapatite (Ca5(PO4)3F or FAP) has been found to uniquely possess superior characteristics as a diode-pumpable Yb-doped medium, in comparison to the properties offered by 14 alternative crystalline hosts (e.g., Y3A15O12 Y2SiO5, LiYF4, BaY2F8, etc.).
Step one toward chaos in a small molecule: high resolution intracavity sub-Doppler spectroscopy of thioformaldehyde
Authors: Clouthier Dennis J.
Published: February 2023

Rotational lines of the S1-S0 band system of H2CS have been recorded with an intracavity sub-Doppler technique at a resolution of 10 MHz. The spectra show numerous extra lines due to interactions of the S1 levels with high rovibronic levels of the ground state, and to a lesser extent with levels of the T1 state. In favorable cases it has been possible to extract coupling matrix elements from the data. The S1-T1 matrix elements are of the order of 1–0.1 cm-1 while the S1-S0 matrix elements are much smaller with values from 6.5 × 10-3 to 1.4 · 10-3 cm-1. The observed perturbations correlate well with observations of level specific anomalously long life times and reduced fluorescence yields in the isolated molecule. The interactions with ground state levels can be classified as step one in the progressive stages of interstate coupling leading to chaos in the optical spectrum of a small molecule.
Vibrational energy transfer in the chemical energy regime
Authors: Wodtke Alec M. , Yang Xueming
Published: February 2023

The dependence of vibrational energy transfer on vibrational excitation has been studied by using the stimulated emission pumping technique to efficiently prepare a large range of specific vibrational states of the nitric oxide molecule in its ground electronic state. Laser induced fluorescence was used to detect collisionally relaxed NO. The self-relaxation rate constants of NO (υ ≫ 1) were up to 200 times that of NO (υ=l). Multiquantum relaxation was found to be important at high energy and was quantified at 3.8 eV. Theoretical explanations of our experimental results were attempted and it is shown that at vibrational energies up to ≈3 eV the qualitative trends observed in these experiments, such as, the mass effect and the linear dependence of the relaxation constant on υ, can be explained by the Schwartz–Slawsky–Herzfeld theory. A simple explanation of the anomalously high NO self-relaxation rate is given. The large acceleration of the vibrational relaxation rate above 3.0 eV is coincident with the energetic onset of high energy (NO)2 isomer complexes. More theoretical and experimental work is needed to explain the quantitative aspects of these observations.
Resonance hyper-Raman scattering from monosubstituted benzenes and naphthalene
Authors: Bonang C. C. , Cameron S. M.
Published: February 2023

Resonance hyper-Raman spectra (RHRS) of monohalobenzenes and naphthalene in solution are obtained by utilizing the intracavity power and 76 MHz repetition rate of a synchronously pumped stilbene 420 dye laser. The nature of one- and two-photon transitions to the 1La electronic state are examined for various halogen sub­stituents. For benzene, vibronic coupling by mode ν12 (b1
u
) makes the 1B1
u
(1La) transition weakly two-photon allowed, suggesting that 1B1
u
couples to the electronic ground state (1A1
g
) more effectively than to any other excited electronic state. Fluorine substitution makes the 1La transition two-photon dipole allowed, while both “weakly” perturbing chlorine and strongly perturbing iodine cause the transition to become strongly one- and two-photon allowed. The spectra confirm that the ≈1600 cm-1 is the totally symmetric ν8
a
mode rather than the previously misassigned ν8b mode. The naphthalene spectrum demonstrates the utility of RHRS for investigating overlapping one- and two-photon allowed transitions.