bluuebunny/crossref_metadata_2025 huggingface dataset:
One-step automatic focus
Authors: Dowski Edward , Cathey W. Thomas
Published: February 2023

With a convolutional image model and a known imaging system, the process of one-step automatic focus reduces to the statistical detection of the deterministic complex zeros of the specific out-of-focus optical transfer function. These complex zeros are independent of the object response and are only a function of the out-of-focus distance and in general lie off the unit circle. With 1-D data samples, a Baysian statistical detector then corresponds to an efficient matrix vector multiplication. This detector can be shown to be a projection of the sampled data onto the null space of the specific optical transfer functions.
Frequency stabilization and measurement of the sequence-band CO2 laser
Authors: Shy Jow-Tsong , Chou Che-Chung , Shieh Chern-Yn , Chern Jin-Dong , Yen Tsu-Chiang
Published: February 2023

The sequence bands of the CO2 laser, which can be generated by placing a hot CO2 cell inside a CO2 laser cavity, provide a considerable increased number of laser lines with sufficient power to pump FIR lasers and for molecular spectroscopy. Shy and Yen have been able to lock a sequence-band laser to the line center using the optogalvanic Lamb dip with a low pressure N2-CO2 dc discharge.1 In this paper, we report two new line-center frequency stabilization methods for the sequence-band CO2 laser. For the first method, which we call rf optogalvanic Lamb dip, the dc discharge is replaced by an rf discharge. This method has certain advantages over the dc optogalvanic Lamb dip: lower pressure, lower operation voltage, no need of water cooling, and better SNR. The second method, saturated 4.3-µm fluorescence, utilizes the fact that the 4.3-µm fluorescence originating from the upper level of the sequence bands does not have the photon trapping effect. We use a longitudinal cell to collect the fluorescence. The cell is a Pyrex tube with inside coated with Al. By heating part of the cell to ~200°C, we were able to observe the saturation dip in the fluorescence signal and use its derivative signal to stabilize the laser. The stability is >100 kHz for both methods. Finally, we measured the beat frequency between a sequence-band laser stabilized by rf optogalvanic Lamb dip and a frequency stabilized regular CO2 laser, and nineteen sequence transition frequencies have been measured to an accuracy of 300 kHz.
Phase matched frequency doubling in poled polymer film waveguides
Authors: Sasaki K. , Nonaka Y. , Nihei E. , Konoshita T. , Koike Y.
Published: February 2023

Frequency doubling in waveguides inevitably requires phase matching by degeneration between the fundamental and the doubled waves in dispersion relation. Furthermore, for higher efficient conversion spatial couplings of those waves must be considered. In the study, disperse red 1(DR1) dye-side-chain copolymer of polymethylmethacrylate (PMMA) was spin-coated with chloroform solvent on a Pyrex substrate at a certain thickness. The poling process was carried out by applying a high electric field (5-kV dc) between the substrate on a metal block and tungsten wire electrode to make a corona discharge at glass transition temperature. The absorption spectrum of the film after poling showed reduction of absorbance accompanying a small red shift corresponding to the orientation of side-chain DR1 molecules.
Holographic recording material for water immersible holograms
Authors: Savant Gajendra , Yacoubian Araz , Aye Tin M.
Published: February 2023

There are several holographic recording materials, such as silver halide, dichromated gelatin, and photoresists; most require extensive processing and do not survive water immersion. We have developed a novel polymeric material that is ideal for holograms that require water immersion and do not need extensive processing. The basic material composition is based on poly-2 hydroxyethyl methacrylate (HEMA) photopolymer that is sensitive in the visible region of the electromagnetic spectrum. We have tested this system, which displayed excellent survivability in water over a period of several weeks.
Determination of binary image contours from the distribution of correlated results
Authors: Lin T. William , Lu Jianyi
Published: February 2023

In optical correlation processes, the intensities of correlation peaks generally serve as the tool for decision-making process in pattern recognition use. The distribution at the correlation plan provides the information for determining the existence of the object being recognized in the references and its whereabouts. However, in a binary pattern recognition process, this distribution at the correlation plane also provides information about the contour of the input object if references are properly chosen. This type of information offers a possibility of updating the reference image when a good match between the input object and the reference images does not exist. Consequently, the reference image can be modified toward the shape of the input image so that an adaptive recognition process can be achieved. In this paper, interpretation of the distribution of correlated result toward the contour of binary input image is investigated. A generalization of these interpretations is formulated and presented. An optical correlator based on joint transform architecture is used to verify the generalized interpretation and the proposed adaptive recognition process.
Nonlinear external cavity dynamics of a fiber laser
Authors: Shore K. A.
Published: February 2023

Considerable activity has been evident recently in the use of lasers coupled to nonlinear external cavities for the generation of short optical pulses. In particular nonlinear optical fibers have been used to effect additive pulse mode-locking (APM).1 In the present paper we report a theoretical study of the utilization of a fiber laser source coupled to a nonlinear fiber external cavity configured for APM. The model developed in this work is of general application and, for example, includes as a special case a description of pulse effects in fiber laser amplifiers. The model utilizes numerical techniques for solving the nonlinear Schroedinger equation appropriate to both the active gain medium of the fiber laser and the passive external cavity nonlinear fiber.2 It is shown in this work that a variety of pulse phenomena may arise in the all-fiber coupled cavity configuration depending upon the operating conditions of the fiber laser. The anticipated pulse narrowing is seen but pulse breakup may also occur. Prospects for high repetition frequency short pulse production are considered.
Imaging diffuser obscured objects
Authors: Welch Gisels , Rhodes William T.
Published: February 2023

An image of a planar object obscured by a moving diffuser can be obtained if the diffuser is illuminated by a coherent plane wave and coherence measurements are made on the wave field reflected by the object back through the diffuser. The image distribution is given by the intensity that would be observed were the object illuminated directly by a plane wave and the reflected wave allowed to propagate one-half the diffuser-object distance. Improved signal-to-noise ratio is achieved if two-point illumination is coordinated with the two-point coherence measurements. Further analysis shows that (1) similar imaging can be performed even with a fixed diffuser and (2) a simpler noninterferemetric measuring system can be used if the diffuser is a pure phase screen. Partial phase conjugation associated with enhanced backscatter plays the key physical role in this process. An important aspect of the analysis is the decomposition of the object distribution into Fresnel transform components.
Triple correlation for pattern recognition
Authors: Zheng S. H. , Karim M. A. , Gao M. L.
Published: February 2023

The purpose of this study is to combine two valuable concepts: triple correlation and matched filtering. Triple correlation analysis is a method for restoring the quality of a disturbed signal or image. Matched filtering is useful for detecting the presence of a specific pattern within an environment of other patterns or noise.
Laser hardening systems based on nonlinear optical material
Authors: Savant Gajendra , Hirsh Jay , Pelka David
Published: February 2023

The development of agile laser filter is of increasing importance because of the expanding use of tunable lasers in the battlefield. Device requirements include broad bandwidth, near-instantaneous response, and high transmittance at low intensities. Implementation as an ocular protection device imposes additional requirements for field of view coverage and high photopic efficiency for incoherent light. Recently, we have been investigating the suitability of self-induced Bragg grating configurations using third-order Kerr-type polymers and photoinduced nonlinear absorbers. The investigation included the development of methods to avoid coupled-wave phase mismatching to improve the device effectiveness. Numerical results based on theoretical coupled-wave analysis indicate strong attenuation of the transmitted laser radiation.
Femtosecond second harmonic generation and autocorrelation applications using nonlinear poled polymeric thin films
Authors: Knoesen A. , Yankelevich D.R. , Dienes A. , Schoenlein R.W. , Shank C. V.
Published: February 2023

The large second-order nonlinearities and short interaction lengths of poled polymer thin films permit unique ultrashort pulse applications. Second-harmonic generation (SHG) with femtosecond pulses requires the use of extraordinarily thin nonlinear media because of the group velocity mismatch (GVM) between the fundamental and second harmonic waves. This limitation is especially severe for the visible to UV wavelength conversions. The short interaction length of poled polymer films results in negligible pulse broadening of the fundamental and second harmonic pulses. For autocorrelation measurements, since phase matching is not a requirement, the poled films can be readily used at different wavelengths. Experimental results of a femtosecond pulse application feasibility study that uses poled polymeric thin films are presented. For example, the results of an experiment that demonstrate SHG of 14-fs long 630-nm pulses using a poled polymeric film 2.5 μm thick are presented. The efficiency is high for such a thin material: 0.16% has been measured and 0.5% has been determined to be possible. A damage threshold of ~60 GW/cm2 was observed. Since GVM is negligible in the film, this allows the generation of UV pulses as short as a few femtoseconds.
Energy conversion efficiency in nonlinear harmonic generation with nonuniform beams
Authors: Cousins A. K.
Published: February 2023

Eimerl1 has presented a map of harmonic generation efficiency as a function of nonlinear drive and beam dephasing. While useful as a conceptual guideline, this type of analysis is limited by the implicit assumption that the beams involved are both temporally and spatially uniform, i.e., that they are continuous-plane waves. Most beams used in practice have spatially nonuniform (approximately Gaussian, in many cases) profiles. In addition, the need to achieve high nonlinear drives usually requires the pump beams to be pulsed in time, often with crudely Gaussian profile in time. The uniform-beam model predicts a rapid decline in conversion efficiency as the nonlinear drive is increased beyond a certain value; experiments with nonuniform beams typically do not exhibit this behavior. The present work extends the conversion efficiency theory to beams with arbitrary super-Gaussian profiles in both space and time. The resulting total energy conversion efficiencies are presented as maps in the drive-dephasing plane, with the beam profiles collapsed into a single additional parameter. As this beam nonuniformity parameter is increased the maps clearly show that the efficiency roll-off tends to disappear, corresponding with the experimentally observed data.
Modulation index for passive FM locking in semiconductor lasers
Authors: Shore K. A. , Lau C. N.
Published: February 2023

In earlier work1 the role of gain nonlinearities in effecting self-locked FM oscillation in semiconductor lasers was established. In FM operation, the longitudinal modes of the laser become equally spaced in frequency and the cavity modes form a single frequency-modulated (FM) optical wave: the so-called FM supermode. The requisite gain nonlinearities and lasing field intensities have been shown to be consistent with the experimental observations of Tiemeijer et al.2 To demonstrate the occurrence of intrinsic FM locking in semiconductor lasers, it is sufficient to utilize a three-mode laser model, but to establish the depth of FM modulation in the self-locked state it is necessary to extend the model of Ref. 1 to take more than three modes into account. In the present paper we describe calculations made using a multimode model of the FM-locking dynamics of laser diodes and specifically report results obtained for a seven-mode model. It is found that an FM modulation index of ~1.8 is obtained for parameters typical of long- wavelength laser diodes.
Status of the lockhead 57-actuator AO system
Authors: Smithson R. C. , Acton D. S.
Published: February 2023

Lockhead has operated a fifty-seven-actuator adaptive optics system in solar astronomy for several years. In this system, the wavefront phase distortions are measured with a Hartmann wavefront sensor and corrected by a nineteen-segment adaptive mirror. In the past, the Hartmann sensor used quadrant array detectors to make the phase measurements. We have recently tested a Hartmann sensor that uses position sensing devices instead of quad-cells.
Dynamic erasable dye-polymer for all-optical neural networks
Authors: Savant Gajendra , Wang Liping , Hirsh Jay
Published: February 2023

Thus far, neural network models have mostly been implemented on computers and electronic hardware. Although there is a potential for optics to offer high density parallel interconnects at high speeds, optical neural network implementation has been limited to single layer machines confined to solving only a very narrow range of pattern recognition problems. Multilayer neural networks are much more powerful than the single layer machines, because they represent a class of universal approximators; however, no practical implementation has yet been reported. The primary reason for this slow progress in the optical implementation of neural networks is the lack of suitable materials that can provide dense, modifiable synaptic interconnections. As a result of broad material research efforts in organic/polymer media, we have developed a new dynamic holographic erasable dye-polymer material. Using this material, high efficiency polarization holograms can be recorded, selectively enhanced or erased in real time, so that dense, modifiable neural interconnects can be implemented.
Analysis of 1-D antireflection structured surfaces
Authors: Raguin Daniel H. , Morris G. Michael
Published: February 2023

Over the past two decades, there has been considerable interest in the use of subwavelength-sized surface-relief features to create antireflection surfaces (ARSs). Because the surface features are small compared to the wavelength of the incident light, the incident light averages over the profiles in question and behaves as if it were encountering an effective medium that had optical properties between those of the incident medium and those of the substrate. By properly designing these surface-relief features, one finds that Fresnel reflections can be remarkably reduced from those produced by a smooth surface. In this research, 1-D ARSs possessing continuous triangular and sinusoidal profiles are modeled theoretically. By analyzing the structures using effective medium theory, closed-form solutions for the reflectance from AR surfaces are obtained. The solutions are found by treating the AR surface as a gradient-index medium and applying Maxwell’s equations along with transmission line theory. For the triangular profile, exact solutions are obtained using Hankel functions, while for the sinusoidal profile, a Ricotti differential equation is solved under the condition that the surfaces reflect <1% of the incident light. Numerical analysis of these AR surfaces was also conducted using rigorous coupled wave theory.1,2 Both the theoretical and the numerical treatment reveal that properly designed 1-D AR surfaces are insensitive to the polarization of the incident radiation and exhibit low reflectivities over a wide range of angles and wavelengths.
Recent studies of a new optimizing technique for computer-generated holograms
Authors: Ersoy O. K. , Sponaugle James
Published: February 2023

Computer-generated holograms are often optimized by techniques such as error diffusion, projections onto constraint sets (POCS), and direct binary search. Earlier, we introduced a new method based on interlacing a number of subholograms,1 each subhologram is optimized by a well-known algorithm, such as the POCS, to correct the remaining reconstruction error. The resulting technique is fast, has excellent error performance, and has the potential to reduce local minima problems.
Remote sensing of object shape using a wavelength scanning laser radar
Authors: Shirley Lyle G.
Published: February 2023

A laser radar prototype has been developed for determining an object’s shape and estimating its surface scattering properties. In this system the target models are flood illuminated with a frequency scanning Ti:sapphire laser. As the frequency changes, the speckle pattern in the backscattered light appears to boil; the time-varying intensity carries information about the object’s range-resolved laser radar cross-section U(z). If the frequency is scanned linearly in time, the power spectrum of the intensity fluctuation at a single point provides a speckled estimate of the autocorrelation of U(z). The speckle is smoothed by low-pass filtering, scan averaging, or averaging estimates from multiple detectors. In a laboratory setting U(z) can be obtained directly from the power spectrum measurement by placing a reflective reference plane behind the object. In general, U(z) can be reconstructed from a higher-order spectrum, the bispectrum. In either case, U(z) is determined uniquely and provides a fingerprint for the object at the given aspect angle. The main advantage of this type of laser radar is its high range resolution, which can be >1 mm. Given U(z) as a function of aspect angle, the object shape can be reconstructed by reflective tomography. The result is a function of position representing the object shape, i.e., zero valued outside of the object bounds. Its value inside the object is related to the surface scattering properties, e.g., the reconstruction tends to fill in more uniformly as the scattering becomes more diffuse. Illustrative measurements are presented for simple shapes including cones, spheres, and cylinders. Parameters, such as sphere radius and cone half angle, are extracted.
Retrieval of particle size distribution function from optical measurements using the downhill simplex method
Authors: Sun Feng , Lewis James W. L.
Published: February 2023

The determination of particle size distribution p(r)m, σ, r) (r= particle dimension, rm= , σ = ) from scattering/extinction data that can be expressed as has long been investigated and several methods have been developed. The downhill simplex is a nonlinear curve fitting technique which, by assuming a suitable two-parameter distribution f(r
m
, σ, r), evaluates the distribution at any three sets of (r
m
, σ) and then changes the parameters in a special way until q, the deference between trial data t = K·f and s = K·p reaches minimum.
Experimental evidence for distinct classes of coupling mechanism in intramolecular vibrational redistribution
Authors: Bethardy G. A. , Go Jungsug , Perry David S.
Published: February 2023

Sub-Doppler infrared absorption spectra of jet- cooled 1-butyne and trans-ethanol exhibit contrasting patterns of molecular eigenstates. In the presence of intramolecular vibration energy redistribution, frequency resolved spectra reveal that transitions to zero order upper state, v, J, K
a
, K
c
levels are fragmented into clumps of molecular eigenstates. The number and frequencies of these discrete features contain information about the nature of the intramolecular coupling. In the methyl C-H stretch of ethanol at 2990 cm-1 between J = 0 to 2, the number of coupled states increases sharply and is comparable to the rovibrational state density. In contrast, the actetylenic and methyl C-H stretches of 1-butyne at 3333 cm-1, respectively, exhibit coupling that is approximately independent of J and coupled state densities comparable to the purely vibrational state density. It is therefore concluded that a rotationally mediated coupling mechanism such as Coriolis or centrifugal coupling is involved in ethanol whereas only anharmonic coupling is apparent in 1-butyne.
High resolution infrared spectroscopy as a tool to measure chemical reaction dynamics
Authors: Philips Laura A. , Brummel Christopher L. , Mork Steven W.
Published: February 2023

Both intra- and intermolecular interactions play an important role in determining the potential surface for a chemical reaction. Such interactions determine both physical structure and chemical reactivity. High resolution infrared spectroscopy has been used to probe both molecular structure and vibrationally induced chemistry. 2-fluorethanol is an example of a molecule in which the strong attractive interactions between F and the OH moity not only determine the lowest energy conformation of the molecule, but also the most efficient vibrational excitation for inducing conformational isomerization. An analogue of 2-fluoroethanol, 1,2-difluoroethane, although similar in structure, has quite different intramolecular interactions. These differences are apparent in both the isomerization dynamics and the spectroscopy. Spectra were measured using a color center laser with optothermal detection (resolution = 10-4 cm-1). The spectra of these molecules allow us to link vibrational mode-coupling to chemical reactivity.
Winner-take-all VLSI/liquid crystal spatial light modulators
Authors: Slagle Timothy M. , Wagner Kelvin
Published: February 2023

This paper describes an optical implementation of a winner-take-all (WTA) function using a VLSI/liquid crystal spatial light modulator. The WTA function evaluates an array of continuous valued inputs and produces a binary output vector with components that are true for the largest of the inputs (the winner) and false for the others. The WTA function is used in neural network models such as competitive learning and for associative memories and correlation plane detectors. Optical implementations of these systems require a WTA with optical inputs and outputs. VLSI/liquid crystal devices provide photodetectors for optical inputs, liquid crystal modulators for optical outputs, and electronic circuitry to implement the globally nonlinear WTA function.
Infrared-pumped green and blue upconversion lasers
Authors: Lenth Wilfried , Macfarlane Roger M.
Published: February 2023

Upconversion lasers operate at wavelengths that are shorter than those used for pumping. Efficient upconversion lasing has been achieved in rare earth-doped materials using several different ex citation processes such as sequential two-photon absorption, energy transfer upconversion and a so-called absorption avalanche mechanism; in the latter case, the pump photons are not resonant with absorption from the ground state.1 All these processes involve the use of metastable, intermediate levels which act as a storage reservoir for pump energy. Following the demonstration of the first cw-pumped upconversion laser in 1986, we have achieved upconversion laser operation at violet, blue, green and red wavelengths in several fluoride host crystals doped with Nd3+, Ho3+, Er3+, and Tm3+ ions by pumping with cw dye, Ti:sapphire or diode lasers.1 These upconversion lasers operate at temperatures up to ~ 140 K using pump powers of a few hundred milliwatts. The use of longitudinal pumping of short, monolithic laser crystals resulted in fairly high pump intensities, which is important for these nonlinear excitation processes. Multistep upconversion excitation has been achieved in Er:YLiF4 by producing laser oscillation at 470 nm from the 2P3/2 level whose energy is more than three times higher than that of the 969-nm light used for pumping. At 77 K, green 551-nm laser output was obtained by pumping a 2-mm long Er:YLiF4 crystal with a 809-nm GaAl As diode laser. Recently, green and blue cw upconversion lasing at room temperature has been reported using fluorozirconate fibers doped with Ho3+ and Pr3+, respectively.2
Praseodymium-doped fluorozirconate glass fiber upconversion laser
Authors: Tropper A. C.
Published: February 2023

Infrared-pumped upconversion lasing of praseodymium ions in a fluorozirconate glass fiber at room temperature has been observed in our laboratory at 491,520,605,635, and 715 nm. For all these transitions the initial state is the 3P0 level at 21 000 cm-1, populated by a two-step pumping process using Ti:sapphire lasers at diode compatible wavelengths; 1.01 μm and 835 nm. The observed threshold powers suggest that diode-pumped operation of these upconversion laser transitions should be readily achievable. Elsewhere the use of codoping to pump this system at a single wavelength has also been demonstrated. In waveguide geometry modest pump powers can achieve large transition rates, an important advantage in this system where the intermediate pump level has a lifetime limited by nonradiative decay to 100 μs. The 4-level 635-nm transition, which exhibited the highest gain, yielded a maximum output of 185 mW when pumped by a total of 2.7 W of infrared power. The efficiency of the pumping process was further demonstrated by operation on the quasi-3-level blue transition at 491 nm. Output powers of up to 40 mW have been achieved at this wavelength.
Contrast sensitivity functions measured during dark adaptation and on steady backgrounds
Authors: Hahn Lance W. , Geisler Wilson S.
Published: February 2023

To compare the effects of bleaching adaptation and background adaptation on spatial vision, we measured contrast sensitivity functions (CSFs) during dark adaptation and on steady back grounds of various luminances. Measurement of the CSFs during dark adaptation (without adding a steady background) required designing a special stimulus. This stimulus was the sum of a 2-D Gaussian blob (intensity A) and a 2-D Gaussian-damped sinewave (amplitude A) with a bandwidth of 0.5 octaves. To prevent detection from being mediated by the Gaussian blob, the sinewave component was added in either a + or – 45° orientation and the subject had to judge the orientation. Thresholds, for spatial frequencies from 1 to 15 c/deg, were measured following full bleaches and on backgrounds from 0 to 10,000 td. Like earlier studies, we observed the square-root law for high spatial frequencies and Weber’s law for low spatial frequencies. In other words, as background luminance increased, the CSF increased at high spatial frequencies relative to low. In contrast, the shape of the CSF was nearly invariant during dark adaptation.
Lateral interactions among contrast sensitive mechanisms
Authors: Cannon Mark W. , Fullenkamp Steven C.
Published: February 2023

We have previously demonstrated suppression of the apparent contrast of a small centrally viewed, 0.25 contrast, sinewave grating patch by a peripheral grating, of 0.5 contrast, presented in an annular surround of variable width.1 We conducted two new experiments with eight subjects to extend our understanding of these lateral interactions by using several central patch contrasts and several surround to center contrast ratios. Experiment 1 determined how center apparent contrast changed as surround size, central patch contrast, and surround to center contrast ratio were changed systematically. This experiment revealed that central patch suppression is not universal for all subjects in all conditions studied. While two subjects did show universal suppression, two other subjects showed almost universal enhancement, and the other four showed a systematic change from suppression to enhancement as stimulus conditions changed. Experiment 2 investigated lateral interactions over a much larger surround to center contrast ratio at a fixed surround width. These data indicate that all subjects show suppression for surround to center contrast ratios of 4.0 and higher. Enhancement, when it exists, occurs only for surround to center ratios between 0.5 and 4.0. The data indicate that contrast perception for complex stimuli may be mediated by an interaction of both excitatory and inhibitory interconnections among contrast sensitive mechanisms. Possible reasons for the different types of behavior across subjects with essentially normal vision are discussed.
Real-time analog electronic pseudocolor encoding based on an optical processing method
Authors: Jutamulia Suganda , Toyoda Shinji , Fujita Akihito , Ito Eiichi
Published: February 2023

Pseudocolor display is developed to increase the visually distinguishable levels. Pseudocolor display can be generated by an electronic digital system or an optical processor.1,2 The principle of the optical method is as follows: Positive and Negative images of the gray-level input are en coded with two primary colors, for example, red and blue. Then the product of the positive image and the negative image is encoded with the third primary color, in this case, green. The superim position of these three color-encoded images results in a pseudocolor image of the gray-level input. We develop an analog electronic system in which a monochrome gray-level video signal is directly transformed into red, green, and blue video signals similar to the optical method mentioned above. If the gray-level intensity signal is denoted by I(t), where 0 ≤ I(t) ≤ 1, color signals are generated as follows: R(t) = I(t), B(t)= 1−I(t), and G(t) = I(t)[1−I(t)], where R(t), B(t), and G(t) are red, blue, and green signals, respectively.
Electrooptic switch using speckle holography
Authors: Yu Francis T. S. , Wu Shudong , Rajan Sumati , Yin Shizhuo
Published: February 2023

Recently we have proposed the use of multimode optical fibers for optical sensing utilizing speckle hologram techniques. In this paper the feasibility of using the fiber speckle hologram techniques for optical switching is demonstrated. Traditional methods of optical switching employ mechanical means to make or break optical paths, or non-mechanical electrooptical (EO) switches based on polarization rotation. The mechanical methods are slow (1-100 ms). Though the EO switches are faster they are bulky and cumbersome to construct and use. To overcome these disadvantages we propose the use of fiber specklegram as a less clumsy and faster optical switching technique. A hologram is formed using a speckle pattern and a spherical reference beam. The transmission hologram thus formed is recorded using a LiNbO3 crystal. On illumination by just the speckle field, the hologram can partially reconstruct the reference beam yielding some information encoded in the speckle field. The reconstruction of the hologram is sensitive to changes in the speckle field. By utilizing this property, and multiplexing more than one specklegram an EO switch has been designed. The design and uses of such a switch are discussed, and the experimental results are presented.
Nonlinear dynamical effects in a periodic waveguide structure
Authors: Sankey Norris D. , Prelewitz David E , Brown Thomas G.
Published: February 2023

Several nonlinear dynamic effects have been predicted to occur in a nonlinear periodic structure including optical switching, gap soliton excitation, and chaos.1 Our experimental investigation utilized a Nd:YAG pulsed laser at λ = 1.064 μm to observe all-optical switching in a periodic silicon-on-insulator waveguide structure. The periodicity of the structure was created by fabricating a Bragg reflector, with a period of 162.5 nm, using electron beam lithography. Two second-order gratings were fabricated on either side of the Bragg reflector to couple light into the waveguide. Transmitted and reflected signals from the Bragg reflector were simultaneously monitored to study the nonlinear dynamic effects in the structure. Measurements were taken at energies ranging from 0.5 to 20 μJ. We have observed all-optical switching and other interesting nonlinear dynamics, including several effects that as yet have no theoretical description.
Self-induced transparency solitons in a nonlinear Kerr host
Authors: Wang Tsun-Yee , Chi Sien
Published: February 2023

We have found a steady-state solution for a pulse propagating in imhogeneously broadened resonant two-level atoms embedded in a dispersive and nonlinear Kerr lossless host medium. The pulse is of an unchirped hyperbolic-secant form with a linear spatial phase delay. There are several salient features in this solution which are different from the results obtained previously. First, for the given parameters of the medium and carrier frequency, the group velocity, the amplitude, and the pulse width are uniquely determined. Second, the group velocity is independent of the density of the resonant atoms. Third, the solution exists in the positive dispersion region, which is different from solitons in fibers.
Polarization ray tracing in anisotropic optically active media
Authors: McClain Stephen C. , Hillman Lloyd W. , Chipman Russell A.
Published: February 2023

We present algorithms for polarization ray tracing through uniaxial optically active crystals, such as quartz, in a form specifically suited for integration into optical design software. These algorithms incorporate ray directions, polarization modes, optical path lengths, and Fresnel transmission and reflection equations. Current commercially available polarization ray tracing software does not perform birefringent ray tracing in uniaxial or optically active materials. The optical designer lacks a straightforward tool for analyzing propagation and aberrations in these media. We apply these algorithms to some examples. For a quartz polarization rotator a misalignment of the crystal axis of 1° is negligible, but a misalignment of 5° renders the device useless.
Three-dimensional optical transfer functions of an optical heterodyne scanning microscope
Authors: Poon Ting-Chung , Raj Kannan
Published: February 2023

Optical scanning systems are broadly used in a variety of imaging schemes in microscopy. However, the image processing operations achievable with a scanning optical system are limited to those corresponding to a real and positive point spread function.1 An optical heterodyne laser scanning system has been introduced to overcome the constraints.2 Here, we investigate the defocusing imaging effect on the optical transfer function (OTF) of the optical heterodyne scanning system and discuss the synthesis of OTFs from defocused 2-D OTFs. Through analytical and simulation results, we show the synthesis of 3-D OTFs using two spatially separated scanning Gaussian laser beams as one example, and two superimposed Gaussian beams apodized by complementary Fresnel zone plates as another example. Low frequency de-emphasis of the obtainable 3-D OFTs is achieved.
Antireflection coatings with reflectance controlled in the visible and far infrared spectral regions
Authors: Li Li , Dobrowolski J. A. , Sankey J. D. , Wimperis J. R.
Published: February 2023

Antireflection (AR) coatings are important components of optical instruments and many papers have been published on their design. However, few deal with the design of dual band AR coatings except for the special case of wavelength doubling or tripling. There is, in addition, a need for AR coatings that act in widely separated spectral regions. For example, when visible lasers are used for the alignment of infrared lasers, the optical surfaces should have AR coatings that are effective at both laser wavelengths. In the case of CO2 and He-Ne lasers, the wavelength ratio is about 17 to 1. Two methods for the design of such AR coatings are described. One is based on the elimination of visible light reflection at the interfaces of the AR coating for the infrared region. The other method uses the concept of a thickness-independent buffer layer.1
Desensitization of optical multilayers to thickness errors
Authors: Ho F. C. , Dobrowolski J. A.
Published: February 2023

Previous work on the desensitization of the performance of optical multilayer designs to production errors in the construction parameters is reviewed. Two new methods developed at the NRCC are described. The first makes use of a compound merit function, which is composed of the basic merit function describing the performance of the system and another term based on the derivatives of this basic merit function with respect to the construction parameters. In the second method, a systematic search is performed in the construction parameter hyperspace over a volume that is centered on the parameters of the starting design and which is defined in terms of the likely construction parameter errors. The second method has the advantage that it can be used for systems composed of many layers. Both methods are illustrated by numerical examples.
X-ray microscopy studies of biological specimens in their natural state
Authors: Schmahl Gunter
Published: February 2023

First, an improved x-ray microscope is described which is installed at the BESSY electron storage ring in Berlin. The x-ray optical setup consists of an x-ray condenser zone plate and a high resolution microzone plate. Both types of zone plate are germanium phase zone plates. They are produced in our institute by ultraviolet laser lithography and electron lithography with zone widths down to 30 nm. X-ray microscopy studies of biological specimens in their natural state (chromatin structures of chromosomes, cytoskeleton structures, etc.) are performed with this microscope with 2.4-nm radiation.
Theory and measurement of surface and bulk scattering in optical multilayers used as classical filters or waveguides
Authors: Amra C. , Bruel L. , Cleva F.
Published: February 2023

Last year we showed how to separate substrate effects from all other effects in a study of light scattering from optical multilayers. In particular, we gave the residual roughness values for different materials obtained by IAD and IP processes. These values explain the additional scattering characteristic of the materials and are not due to reproduction of substrate defects.
Coating and substrate surface roughness
Authors: Guenther K. H. , Tehrani M. M. , Bennett Jean M.
Published: February 2023

Mirror scattering, which is an important factor in a number of instruments including the ring laser gyro, is largely determined by the surface roughness. The question is to what extent is the latter influenced by the coating material and process. To answer this, a number of substrates were surface profiled using the (noncontact) Zygo optical heterodyne profilometer. Of these, two each were coated with one, two, and four half-waves of titania using the reactive ion plating (RIP) technique. A similar set of coatings using silica were produced as well as two multilayer stacks of titania/silica. Ail samples were surface profiled after the coating. Results indicate no statistically significant change in the rms surface roughness and, on the average, a slight increase in the peak-to-valley roughness. Experimental details and the results of both the optical heterodyne profilometry and Talystep measurements are discussed.
Dynamic optical interconnect systems
Authors: Morris James E. , Feldman Michael R.
Published: February 2023

Dynamic optical interconnect systems are being investigated. These systems consist of fixed, high frequency, computer-generated holograms (CGHs) and dynamic spatial light modulators (SLMs). The CGH is used to achieve a high space-bandwidth product that is currently not available in SLMs and the SLMs provide the dynamic properties. Each modulator changes the wavefront that hits a large area of CGH. The CGH is designed so that different wavefronts will send light to different positions. This method allows for local control (modulators in same plane as processors) or external control (modulators in different plane than processors) of the connections. Computer simulations have been preformed on various system configurations to test this theory. Iterative optimization techniques are used to design the CGHs and take into account quantizations in the CGHs and SLMs.
Phase locking of GaAs semiconductor diode lasers
Authors: Rogovin D. , Shen T. P. , Rentzepis P. M. , Depatie D.
Published: February 2023

Beam combination via nondegenerate two-wave mixing (NDTWM) is a nonlinear optical scheme that enables one to transfer energy from a high frequency pump beam to a low frequency probe wave. An important characteristic of this process is that it is not necessary for the pump wave to be phase coherent as the pump photons acquire the frequency, wave vector, and phase of the probe beam. Thus an incoherent pump beam can be used to amplify a coherent probe wave without degrading its optical characteristics and phase-lock the amplified output laser beams. We examine phase locking of semiconductor diode laser arrays via NDTWM in a variety of nonlinear media in either waveguides or optical fibers. The waveguide structures are essential for efficient phase-locking, since they provide large effective nonlinear wave-mixing coefficient. For semiconductor diode lasers whose power levels exceed 100 mW, the emission is usually phase incoherent and this presents a problem for phase-locking by a coherent probe beam. However, if the active medium has a response time that is fast on a time scale set by any changes in the interference pattern of the laser beams, the phase incoherent pump wave may still be phase locked.
Uses of volume holographic optical elements
Authors: Tedesco James M.
Published: February 2023

Several uses that have been developed or proposed for volume holographic optical elements (HOEs) are reviewed. Volume HOEs possess several unique properties that distinguish them from conventional optical elements. These properties include (1) wavelength and angle selectivity, (2) imaging functions relatively independent of surface shape, (3) ability to impart spectral notches that are deep (>5 OD) and steep-sided, (4) high, negative V-number dispersion, and (5) ability to share a single aperture between multiple elements. Several applications that make use of these unique features of volume HOEs have been developed or proposed. Holographic head-up display (HUD) combiners provide high display reflectance simultaneously with high visual transmittance. Curved, highly off-axis holographic HUD combiners provide built-in aberration correction, enabling high image quality over wide fields-of-view in systems having very restricted installation geometries. Notch filters have found use in protection against laser damage for sensors and eyes, attenuation of atmospheric emission lines in remote sensing, and range extension of Raman spectroscopy instruments to lower wavenumber shifts. Rotating HOEs have been used as laser scanners for barcode readers and higher resolution imaging equipment. Holographic gratings are used in multiplexers/ demultiplexers and other monochromator devices to provide both focusing and wavelength separation. Holographic optical interconnects may provide parallel VLSI electronic circuit connections with large fan-out and negligible propagation delay.
Crosstalk limited storage capacity of volume holographic memory
Authors: Hong John H. , Saxena Ragini , McMichael Ian , Mok Fai
Published: February 2023

Angularly multiplexed volume holograms1 are considered for use in optical memory systems where compactness and high storage density are desired features. In such a memory system, an object beam containing a page of information is recorded in association with a uniquely oriented reference beam in a volume recording material such as photorefractive crystals. The procedure is repeated with different sets of object and reference beams to yield a volume memory in which a particular page of information can be uniquely accessed by reading the hologram with the corresponding reference beam. The largest amount of information that such a system can store is upper-bounded by the geometric factor O(V/λ3) where V is the volume of the holographic medium and λ is the wavelength of light.2 A tighter upperbound can be derived by considering the limitations of the medium.3 In this paper, we consider the storage density limiting effects due to crosstalk between the stored pages during readout. We review some earlier work done in this area4 and present new theoretical and experimental work that characterizes the storage capacity limitations from the crosstalk.
Ultimate bandwidth limitations of quantum well lasers
Authors: LaCourse Joanne , Rideout W. , Sharfin W. , Vassell M.
Published: February 2023

Most high frequency quantum well lasers reported so far have been limited either by insufficient power or by electrical parasitics, but this paper addresses the ultimate bandwidth limit, set by damping due to gain suppression:

f

max

=

8

 
π
l
k

, where k = Γ/fO2, where fO is the resonance frequency, and where Γ is the damping rate. This limit is ~30 GHz for bulk lasers but is highly variable for quantum well lasers. Estimated values range from 4 GHz (for 1-μm strained SQW lasers1) to 70 GHz (for 1.5μm strained MQW lasers2). Clearly it is important to understand the cause of this damping, not only for fundamental principles but also to guide the optimization of high frequency quantum well lasers.
Ultimate modulation bandwidth in semiconductor quantum well lasers
Authors: Zhao B. , Chen T. R. , Yariv A.
Published: February 2023

Recent theoretical and experimental work has shown that the use of multiple quantum wells (QWs) in the active region of semiconductor lasers has led to significant improvements in their intrinsic frequency response. Here we derive the relationships among the optimal modulation bandwidth, optical power, number of QWs and other laser device parameters by considering the 2-D characteristics of the injected carriers in the QWs and both the differential gain and nonlinear gain caused damping effects. These results are used to study the modulation bandwidth optimization. The multiple QW structures are superior to single QW structures on modulation bandwidth only in some limited ranges of device parameters, but the optical power to reach the optimized modulation bandwidth decreases as the number of QWs increases. The maximum optimized modulation bandwidth increases as the number of QWs increases, but there is an ultimate limit. Compared with that of the bulk structure lasers this ultimate limit is lower.
Theory of dielectric branching waveguides
Authors: Songwatana Kraisin
Published: February 2023

The optical branching waveguide is analyzed, using the interaction between guided and radiation modes of the main (stem) waveguide. These modes are known to be orthogonal and form a complete set. The electric field in the branching waveguide is therefore assumed to be a weighted sum of these modes and they are coupled through the perturbed boundaries (i.e., the branches). The generated radiation modes are not only a mechanism for radiation loss but also act as a transport medium for coupling between the guided modes of the main waveguide and the branches. The coupling of light between the stem and the branches can then be viewed as a two-step process: (i) the coupling between the guided mode of the stem and the radiation modes, followed by (ii) the coupling between the radiation modes and the guided modes of the branches. This analysis leads to a system of coupled-mode equations involving the amplitudes of the modes. This system of equations is then simplified and solved analytically. Data obtained from the optical measurements on branching waveguides devices fabricated by Ti-diffused into LiNbO3 channel waveguides are also provided to confirm the result of the analysis.