bluuebunny/crossref_metadata_2025 huggingface dataset:
Optics in particle contamination inspection
Authors: Batchelder J. S. , Taubenblatt M. A.
Published: February 2023

The continual reduction of printable feature sizes in micro-electronics fabrication will require UV optics and possibly x-ray or ebeam lithography in the coming decade. Since circuit patterns are typically adversely affected by particles one tenth of the minimum feature size, optical particle detection will be required to operate well into the Rayleigh limit, where the scattered light intensities fall as the sixth power of diameter for isolated particles. The resulting marked drop in signal level, plus the need for shorter times between technology introductions and volume manufacturing, leads to a segmentation of sensor technologies into a spectrum of niches ranging from off-line (slow, highly sensitive lab tools) to on-line (stand-alone product inspection on the manufacturing floor) to in-line (in the process flow) to in-situ (in the process chambers). We will outline the required speed and sensitivities for different particulate detection applications over the next ten years.
Microlaser microscope
Authors: Webb Robert H.
Published: February 2023

A scanned laser microscope with no moving parts is described. The source for this device is an array of 250 000 microlasers on a single substrate, each laser being typically 2 mm in diameter. The entire array is imaged on the microscope's object plane, but only one laser emits light at a given instant. Thus, as the array is electronically scanned, the illumination spot moves over the object. In the simplest configuration, a beam splitter returns light from the object to a detector, and the resulting voltage stream is synchronously displayed on a television monitor. The microscope can thus be packaged in a volume of ~1 cm3 (plus electronics). Variants on the basic microscope permit random access to any pixel, transmission microscopy, and a wide range of field sizes. Later versions will incorporate a synchronous solid-state detector array, which makes this a confocal microscope, and multiplexing of the array elements so that the device has both the scanning laser (confocal) microscope's brightness and the tandem-scanning (confocal) microscope's Felgetts advantage. This detector array can be used to run much faster than television scanning rates or to use much less light, thus avoiding fluorophore bleaching. Ultimately, the microscope can be further miniaturized so that it can be introduced into body cavities and other difficult places. Finally, the same technology can be used to make an inexpensive high-brightness display that is small enough to be worn on an eyeglass frame.
From features to solids
Authors: Sclaroff Stan , Pentland Alex P.
Published: February 2023

We present a closed-form, physically-based solution for recovering a three-dimensional (3-D) solid model from collections of 3-D or 2-D features. This method uses the positions of comers, face centers, contours, and edge centers to recover any object that can be generated by smooth deformations of a sphere, e.g., boxes, bowls, bananas, hourglasses, and heads. Given a sufficient number of independent features, the solution is overconstrained and unique, except for rotational symmetries. This method is also effective for recovering 3-D structure from 2-D gray-scale images of line drawings; when only the x and y positions of the features are available, we can generate a good estimate of the unknown z values by finding the 3-D interpretation with the lowest internal energy. A particular advantage of this approach is that the recovered solid model supports extremely efficient shape-comparison and intersection calculations.
Rotation-invariant recognition and generalized autocorrelation
Authors: D'Zmura Michael , Iverson Geoffrey , Yellott John
Published: February 2023

We discuss the problem of how to determine whether two patterns are identical up to some rotation. Much work on this topic in machine vision relies on first-order correlation procedures to determine the magnitudes of the angular-frequency components in the patterns. Because phase information at each frequency is ignored, such strategies identify patterns that are not related by a rotation. How can we capture this phase information, which is needed for fully rotation-invariant recognition? Generalized autocorrelation functions1 provide increasingly more information about relative phases at each angular frequency as the order of the generalized autocorrelation is increased. We examine the conditions on image patterns under which nth-order autocorrelation functions can be used for fully rotation-invariant recognition. The results show that for many applications fully rotation-invariant recognition can be achieved only through generalized correlation procedures that are computationally intractable. We show that this difficulty in capturing the rotation-invariant aspects of patterns extends to many groups of transformations of interest in vision research that have as a subgroup the group SO(2) of rotations.
Perceptual asymmetries in texture segregation can be explained by bottom-up processing alone
Authors: Williams Douglas , Julesz Bela
Published: February 2023

For certain texture pairs, the ease of perceptual segregation changes when the roles of targets and distractors are switched. For example, it is far more difficult to detect an array of circles in a field of ellipses than vice versa. Similarly, it is more difficult to detect an array of straight lines in a field of curved lines than the reverse. The existence of such perceptual asymmetries suggests that the element that is easier to detect (i.e., an ellipse or curve) contains an emergent feature. To further determine the significance of these asymmetries, we studied discrimination with short presentations (40 ms duration) of only two elements: (1) one target and one distractoror (2) two distractors. False-alarm rates for two distractors were much higher if the presentations were composed of the more easily detected element pairs. These results suggest that these elements are not reliably perceived and that their duals are more stable. We therefore conclude that asymmetry is not the result of an emergent attribute. Rather, elements may not be completely resolved because of either short presentation or, in the case of displays composed of many elements (i.e., textures), because of lateral inhibition owing to the limited spatial extent of focal attention.
Performance characteristics of an airborne backscatter lidar operating at 9.25 μm
Authors: Tratt David M. , Menzies Robert T.
Published: February 2023

The Jet Propulsion Laboratory Airborne Backscatter Lidar (ABL) has now participated in three major field campaigns aboard the National Aeronautics and Space Administration Ames Research Center DC-8 research aircraft, which were carried out over the course of one year. This presentation will focus on the design philosophy of ABL and will emphasize how well the instrument has performed throughout its extended deployment. Comprehensive performance-validation exercises have been key features of each individual flight series, so in this regard we are satisfied that ABL is performing to specifications and that the data being produced unequivocally demonstrate the excellent internal and external consistency of the instrumental parameters. Although individual component subsystems have been deficient at various times during this period, each of these issues has been successfully resolved. Additionally, and with few exceptions, the lidar optical integrity has proven remarkably resistant to repeated environmental disturbances, such as aircraft touchdown and inflight turbulence.
Confocal microscopy
Authors: Webb Robert H.
Published: February 2023

Confocal microscopy is an exciting new development in imaging. The same techniques that work for compact-disk recorders make it possible to increase resolution in microscopes and to discriminate so well against scattered light that out-of-focus planes do not spoil the contrast of the focal plane. That, in turn, permits optical sectioning in the transparent objects of biology and optical profiling in metallurgy.
Issues in pulsed laser interferometry and coherence control
Authors: Kessler T.
Published: February 2023

We review the interferometric and wavefront analyses techniques available for the pulsed laser beam. Then we compare these methods to the commercially available systems that are directed towards numeric continuous wave applications. Finally, we explain specific applications of precision interferometry to lasers and laser components.
Texture coding and analysis by Gabor functions
Authors: Tabernero Antonio , Navarro Rafael
Published: February 2023

It is well known that the receptive fields of simple cortical cells can be modeled by Gabor functions. This can be a new and promising way of facing the texture problem. In our presentation we show how the responses of the neurons in the visual cortex can be used as texture descriptors in image analysis tasks—mainly segmentation and classification. We have used a simple Gabor scheme with a pyramid implementation in the spatial domain. Only four orientation channels and four frequency channels have been used. We have also searched for descriptors that are invariant under rotation and scale changing. Equivalent texture analysis results may be expected with other similar schemes, such as the cortex transform. Because this Gabor coding is not complete, there will be some errors during the reconstruction. These errors have been studied, including the effect of missing frequency channels. In spite of these errors, the resulting reconstructed images have good visual quality, except for some typical visual illusions. Because these illusions also appear in the visual system, a similar scheme might be used as a model of the visual system.
Spatiotemporal spectrum of time-varying imagery
Authors: Eckert Michael P. , Buchsbaum Gershon
Published: February 2023

It has been suggested that image representation in the visual system is matched to the spatial statistics of natural imagery.1 The extension of this idea to include time requires the development of a reasonable model of the spatiotemporal spectrum of real-world time-varying imagery.2 We have calculated the spatiotemporal power spectrum of 14 image sequences (256 × 256 × 64 at 30 frames/s with no scene cuts). The sequences include scenes with camera pans, object tracking, and object motion with no camera motion. They represent a small ensemble of time-varying imagery the visual system might encounter in the real world. The spectrum of each sequence was found to be spatiotemporally separable to a large degree and was well fit by a model of the form S(|k|,f) = [(2π |k|/a)2 + 1]− n1 [(2πf/b)2 + 1]−n2,where k and f are spatial and temporal frequencies and a, b, n
1
, and n2 are parameters computed separately for each sequence. Reasonable fits to all spectra (in the mean-squared-error sense) were obtained with n1 = 1.5 and n2 = 1.0, which suggests that the image sequences can also be modeled reasonably well by an exponential autocorrelation function that is spatiotemporally separable.
Observation of dark spatial solitons and study of induced focusing in a self-defocusing medium on a nanosecond time scale
Authors: Kang Keith , Guha Shekhar
Published: February 2023

The advantage of using nanosecond pulses to generate the large thermal nonlinearity that arises from the absorption of laser beams in liquid media is that one can avoid the problems of the spatial nonlocality of the nonlinearity owing to the convection currents and diffusion that are associated with cw beams. By using 10 ns laser pulses that passed through a cross wire placed behind an absorbing liquid, we found evidence of the generation of stable spatial dark solitons from the near-field and far-field patterns generated by low-intensity and high-intensity beams. We also observed evidence of the formation of spatial dark solitons when the cross wire was replaced by a phase plate. We plan to measure the transverse velocity, modulation depth, and other constants of motion and compare them with the theoretically predicted values. The spatial dark solitons are particular solutions of the nonlinear Schrodinger equation, which describes wave propagation in a medium with a large negative nonlinearity. Another consequence of this equation was recently pointed out by Agrawal,1 who showed that for two copropagating but not completely overlapping beams, cross-phase modulation can take place without energy exchange. We have observed large two-beam coupling in thermal media and will present the results of our investigation of the effect predicted by Agrawal.
Detection algorithms for fluorescence lidar with atmospheric extinction, noise, and daylight background
Authors: Rosen David L. , Gillespie James
Published: February 2023

Remote chemical analysis by fluorescence lidar is limited by the problems of background light, multiple-component fluorescence, and atmospheric spectral attenuation. We modeled the detection of chemical compounds from simulated fluorescence-lidar returns by means of rank annihilation-factor analysis (RAFA). RAFA is a set of algorithms for analyzing excitation-emission matrices (EEM). A spectral background consisting of daylight and fluorescence from fly ash was used in our simulation. The target substance to be detected was NO2. The simulated lidar returns were calculated as a function of range, and they included both photon noise and atmospheric extinction. A RAFA detection algorithm was applied to both background-only returns and to background-plus-NO2 returns to determine how the background limits the range at which the components in the mixture could be distinguished. We found that the combination of daylight and photon noise severely limited the RAFA detection algorithm.
Recovery of optical waves by a phase-conjugate mirror in a random medium with loss (gain)
Authors: Tarng J. H. , Yang C. C.
Published: February 2023

It has been theoretically proven that in most situations optical waves, which experience random scattering in a lossless medium, can be completely recovered when reflected by a phase-conjugate mirror. The recovery is not complete, however, if the medium has loss (gain) or if the phase-conjugate mirror changes the wave intensity. When the medium includes random fluctuations of refractive index, such as is brought about by turbulence, the recovery of optical wave deteriorates. The existence of random fluctuations of refractive index in the propagating medium implies random fluctuations of the medium's absorption (emission) according to the Kramers–Kronig relations. In this research, the extent of wave recovery by a phase conjugate mirror in a random medium with loss (gain) is investigated. The wave is propagated through a random medium, reflected by a phase-conjugate mirror, and then propagated back through the same random medium. Because a random system is under investigation, statistical parameters such as average wave field, average intensity, standard deviation of phase, and contrast (scintillation index) are evaluated. These parameters indicate the extent of wave recovery. The Rytov approximation is used, and the planewave assumption is made for mathematical simplicity.
Frequency tuning and control of doubly resonant optical parametric oscillators
Authors: Eckardt R. C. , Yang S. T. , Gustafson E. K. , Byer R. L.
Published: February 2023

The tuning analysis of the doubly resonant optical parametric oscillator (DRO) is extended to provide a quantitative description of spectral hops between adjacent axial modes and the larger discontinuous frequency changes of cluster jumps, which are in agreement with experimental observations. DRO's offer the advantages of lower pump threshold for oscillation and better frequency selectivity than singly resonant parametric oscillators (SRO's), and it has been demonstrated that DRO's can reproduce the frequency stability of the pump radiation with little additional noise.1 These advantages, however, are gained with an increase in the complexity of tuning. Control of three parameters, such as pump frequency, temperature, and applied electric field, is required to attain optimum phase and frequency matching of the cavity resonances for DRO operation. The pump-frequency change is divided between the DRO signal and idler. Temperature change used to maintain phase matching and applied potential is used to maintain frequency matching through feedback techniques. DRO's should find application to slowly tuned or fixed-frequency operation, whereas SRO's have advantages for rapidly tuned and transient-pulse operation. Experimental studies to demonstrate stable fixed-frequency operation and slowly tuned operation of DRO's are in progress.
Meaning of first-order optics
Authors: Stone Bryan D. , Forbes G. W.
Published: February 2023

The concept of first-order properties of axially symmetric optical systems is well known. Of course, the same concept is fundamental in the context of nonaxially symmetric systems. To determine the first-order properties of a system, it is common to perform a differential ray trace, the results of which are conveniently represented in the form of a derivative matrix. From this matrix, any first-order property (e.g., focal length and magnification) of the system can be determined. For imaging systems, one important property is the location of the first-order image. For axially symmetric systems, the derivative matrix can be used to determine the position of the image of the axial point of the object. However, the location of the firstorder image of any other point on the object cannot be determined uniquely. Consequently, there is never a unique paraxial image plane. This concept and its extension to the nonaxially symmetric case are discussed. Although the extension is straightforward, it has caused some confusion in the literature (e.g., see Ref. 1 and the references cited therein). The aspects of the problem that have contributed to this confusion are addressed in an attempt to shed some light on this situation.
Hopfield neural network using electron-trapping materials
Authors: Jutamulia Suganda , Stroti George M. , Seiderman William , Lindmayer Joseph
Published: February 2023

The electron-trapping (ET) materials are optical storage materials developed by Quantex. When ET materials are exposed to visible light (e.g., 488 nm), electrons from the ground state are excited and then captured by thermally stable traps. Subsequent exposure to IR light (e.g., 1064 nm) excites and releases the trapped electrons to the ground state with the emission of orange-to-red light. The ET materials are capable of performing multiplication, addition, and subtraction within a dynamic range covering four orders of magnitude. The orange emission intensity is proportional to the product of the blue write-in intensity and the IR read-out intensity. The addition and subtraction operations are performed by increasing and decreasing the number of trapped electrons. An ET thin film can be used as an optical mask to perform matrix vector multiplication. Furthermore, the ET thin film has an inherent capability for summing, subtracting, and storing optical data, in addition to multiplication. This extra capability, which is not commonly found in spatial light modulators, will be used for the optical formation of an interconnection matrix (prescribed learning).
Measurement of frequency locking in phase-conjugate optical gyroscopes
Authors: Rosker M. J. , McMichael I. , Saxena R.
Published: February 2023

A ring resonator containing a phase-conjugate mirror can act as a phase-conjugate optical gyroscope (PCOG).1 The frequencies of the counterpropagating oscillations depend on the nonreciprocal, but not on the reciprocal, optical path length of the resonator; thus, the device is potentially useful for inertial sensing of rotational motion. A primary limitation of conventional ring-laser gyroscopes is frequency-locking behavior, wherein backscattering couples the counterpropagating laser oscillations. Our previous theoretical results2 indicated that, for nonreciprocal phase shifts of ~π/10 rad, frequency locking occurs when the ratio of backscattered light to pump light exceeds ~10-3. We describe our experimental investigation of the frequency-locking characteristics for the ring PCOG. A weak seed beam was injected into the oscillator along the same direction as the phase-conjugate output. The frequency difference between the counterpropagating waves was measured as a function of the seed intensity and the nonreciprocal phase shift. Measurements were made with both coherent and incoherent (with respect to the pump) seed light to simulate scatter contributed by the phase-conjugate and conventional mirrors, respectively. The experimental results are in good agreement with theory.
Optical scale-space–based morphological processor
Authors: Fedor A. , Freeman M. O.
Published: February 2023

Mathematical morphology is a branch of mathematics that has proven its usefulness in many image-processing and computer-vision problems.1 We present the application of an optical-centroid scale-space processor for the computation of basic morphological operations. The centroid scale-space map2 extracts centroids of the image that are defined within a local neighborhood whose size is specified by the kernel (x + iy) limited by a circular window. Properties of these centroids, as they are tracked through scale, permit one to obtain a great deal of information from the image in a simple and straightforward manner. One property of these maps is that solid regions of centroids are produced when the kernel is completely enclosed within a constant region of the input. One may use this information to compute various morphological transformations, such as erosions, dilations, and medial-axis transformations (MAT). Redundancies in the representation result in a method for the MAT that is robust in the presence of noise. In addition, the map works simultaneously on all constant regions of a gray-level image. The optical system is based on a joint-transform correlator that uses an optically addressed ferroelectric liquid-crystal spatial light modulator. A complete range of scales is scanned by winking an iris between open and closed. Results from this optical system will be presented.
Non-ideal thresholding effects in the optical implementation of median filtering
Authors: Hereford James M. , Rhodes William T.
Published: February 2023

Median filtering can be performed optically on a gray-scale input by decomposing the input into a seriesof binary cross sections, convolving each cross section with a binary kernel of the desired shape, thresholding the convolution output, and summing the filtered cross sections to form the gray-scale output. A potential problem in the optical implementation of this method is finding a spatial light modulator to perform the thresholding. We studied whether it is possible to obtain adequate results with nonideal (soft) thresholding. A numerical simulation was used to evaluate the effects of soft transfer curves with different slopes. The simulation produced a startling conclusion: It is better not to have ideal thresholding when performing median filtering. Better grayscale outputs were obtained with transfer curves that had a finite transition region rather than an ideal step response. This bodes well for the possibility of a real-time optical implementation of median filtering with real devices.
X-Ray Focusing Using a Flexible Hollow-Core Tampered Glass Fiber
Authors: Thiel Daniel J. , Bilderback Donald H. , Lewis Aaron , Stern Edward A.
Published: February 2023

A new method of focusing x-rays using a tapered, hollow glass fiber is being developed. By directing an x-ray beam down the bore of such a fiber, one can obtain increased intensity since the guided radiation suffers only slight loss upon repeated total reflections from the air/glass interface of the inner wall. The fiber must be drawn so that the angle of taper of the inner diameter is small compared to the critical angle of the impinging x-rays. We have overcome this challenge by drawing fibers with taper angles as small as 0.1 milliradians. A 1.6 meter long hollow fiber with an inner diameter that decreased linearly from 470 to 110 microns was tested using monochromtic synchrotron radiation of 8.04, 13, and 20 keV as well as characteristic radiation from a conventional x-ray tube with a copper target. Transmission and focusing characteristics are reported. Intensity enhancements as large as 10 corresponding to a transmission efficiency of 54% were observed. The high efficiency of this prototype fiber supports the notion that this confinement technique should yield gains of many orders of magnitude as the optimal fiber design is achieved.
Picosecond Spatial Soliton Induced Trapping of Weak Probe Beam
Authors: de la Fuente R. , Barthelemy A. , Froehly C.
Published: February 2023

It was predicted serevai years ago that the balance between diffraction and self-focusing in a Kerr type nonlinear medium leads to the propagation of a spatially stable wave under suitable initial conditions (1). These waves named spatial or geometrical solitons have already been observed in liquids, gases, and glasses (2-4), and require twodimensional propagation. On the other hand it has been theoretically pointed out (5) that it is possible for a strong pump beam to induce the trapping of a probe wave superimposed on the pump by means of cross phase modulation. However this approach neglects the fact that inevitably a cylindrical beam breaks up under chaotic self-focusing in threedimensional propagation.
Experimental Test of the deBroglie Guided Wave Theory for Photons
Authors: Wang L.J. , Zou X.Y. , Mandel L.
Published: February 2023

An experiment has been carried out to test a prediction of the deBroglie guided wave theory for photons. According to this theory, there exist electromagnetic waves as well as photons, with the former acting as guide for the latter. The wave not only determines the probability for the detection of a photon, but it also has an independent physical reality which can result in photodetection, As a result the guided wave theory predicts an interference effect when two photons pass through an interferometer with a particular geometry and one measures the rate of simultaneous detections by two photodetectors in coincidence as a function of optical path difference, By contrast, quantum mechanics predicts no interference under the same conditions. The experimental results clearly violate the prediction of the guided wave theory, but are in agreement with quantum mechanics.
Demonstration of Photorefractivity in Organic Polymers
Authors: Ducharme S. , Scott J. C. , Twieg R. J. , Moerner W. E.
Published: February 2023

Polymeric nonlinear optical materials offer a number of potential advantages over inorganic materials, particularly low cost of material, low dc dielectric constant, ease of fabrication, and compatibility with integrated optics. We report here for the first time firm evidence of photorefractivity in a nonlinear optical polymer. Photorefraction (at 647.1 nm) was established by a combination of hologram erasability, correlation with photoconductivity and electro-optic response, and enhancement by external fields in numerous samples (178 to 533 µm thick) of the polymers (BisA-NPDA)1 or (NA-APNA)2 mixed with hole transport agents such as p-diethylaminobenzaldehyde-diphenyl hydrazone (DEH). Diffraction efficiencies up to 0.1% (NA-APNA) and 0.06% (BisA-NPDA) were observed at bias fields of 84 kV/cm and 126 kV/cm, respectively. The calculated space-charge field in one sample of the BisA-NPDA mixture was 47 kV/cm (the largest yet reported in any photorefractive material) at 126 kV/cm and a grating spacing of 0.2 µm; the estimated photorefractive trap density was 6 × 1015cm−3.
Metastable xenon: a new optical clock
Authors: Rolston S. L. , Phillips W. D.
Published: February 2023

The possibility of a neutral atom-based "ultimate" frequency standard in the optical domain has improved dramatically with the discovery of sub-Doppler cooling mechanisms. Unfortunately, the atoms with clock transitions of order 1 Hz that have been identified will be extremely difficult to laser cool. We have identified a two-photon transition in metastable xenon (3P2→3P0) at 2.19 microns with a calculated linewidth of 2 Hz. Metastable xenon can be laser-cooled with a cycling transition at 882 nm, convenient for Ti:sapphire lasers, with cooling parameters almost identical to cesium. Expected temperatures should be about 3 microkelvin, which will allow a fountain to be constructed that has little loss of signal due to spatial spreading of the atoms. After making the 2-photon clock transition, the atoms that are in the 3P0 metastable state can be detected with high efficiency with a metastable detector. Atoms in the lower metastable state can be completely removed by applying small amounts of diode laser light at 828 nm to drive atoms into the ground state, allowing high efficiency, essentially background-free detection. Two-photon transition rates and AC stark shifts have been calculated and will be presented. Possible laser sources for the clock transition will be discussed, as well as a connection from this optical frequency to the microwave.
Recent advances in long-haul optical fiber transmission systems using erbium-doped fiber amplifiers
Authors: Edagawa Noboru
Published: February 2023

Abstract not presently available.
Optical nonlinearities in transoceanic lightwave systems with fiber amplifiers
Authors: Tkach R. W. , Chraplyvy A. R. , Marcuse D.
Published: February 2023

Optical amplifiers permit the-extension of transmission distances in lightwave systems to several thousand kilometers before the accumulated noise causes unacceptable errors. When the signal power is maintained over these long distances, optical nonlinearities become a dominant concern. The nonlinearity of silica fibers can be expressed as an intensity-dependent refractive index, n = n0 + n2I, where n2 = 3.2 × 10−16 cm2/W. There are three major manifestations of the nonlinear index: self-phase modulation, in which fluctuations in the signal power give rise to a modulation of the signal phase and lead to a broadening of the spectrum; cross-phase modulation, in which intensity fluctuations of a second channel propagating in the fiber modulate the phase of the first channel; and four-photon mixing,1 in which the beating between two channels modulates the signal phase at their different frequencies, generating new tones as sidebands. In amplified systems, noise can act as a second channel for cross-phase modulation or four-photon mixing. The choices for modulation format fall into three categories: on-off keying, the standard format of today's systems; constant envelope modulation, such as phase-shift keying, which minimizes power fluctuation of the signal; and soliton transmission,2 which uses pulses formed by balancing selfphase modulation and dispersion. We will describe various nonlinear effects and the constraints they impose on possible systems.
Amplification of ultrashort optical pulses in fiber amplifiers
Authors: Agrawal Govind P.
Published: February 2023

An erbium-doped fiber amplifier has the potential of amplifying ultrashort optical pulses1,2 to microjoule levels because of its wide gain spectrum and high saturation energy. A modeling of the amplification process in such amplifiers should include not only the gain saturation and gain dispersion associated with the erbium dopants but also groupvelocity dispersion and Kerr nonlinearity associated with the host material. Furthermore, the soliton effects should be expected to play an important role because of anomalous dispersion. In this paper we derive a propagation equation for the pulse amplitude by including the above effects and solve it numerically to study the amplification process. Two cases are considered separately. In the first case, the pulse energy is assumed to remain below the saturation level, so that gain saturation is negligible. The input pulse is compressed as it is amplified without significant changes in the pulse shape. Gain dispersion sets the ultimate limit on the extent of pulse compression.3 In the second case, gain saturation is included, but gain dispersion is neglected. The pulse shape is distorted because its leading edge sees larger gain than the trailing edge sees. We study the temporal and spectral changes occurring during the amplification process through detailed numerical simulations.
Signal propagation and noise accumulation in amplified lightwave systems
Authors: Giles C. Randy
Published: February 2023

Lightwave systems using optical amplifiers as repeaters offer the advantage of ease of capacity enhancement through the use of either high data rates or wavelength-multiplexed channels. Besides optical fiber nonlinearities, potential limitations of such lightwave systems include the effects of optical amplifier saturation and the accumulation of amplified spontaneous emission. Simulations show that transmission at gigabit-per-second rates over transoceanic distances is possible if erbium-doped fiber amplifiers are used as repeaters. The upper limit on amplifier spacing imposed by noise accumulation is approximately 100 km for a 10000 km, 2.5 Gb/s transmission system. Reduced amplifier spacing lowers the total noise and expands the range of signal powers that satisfy the required signal-to-noise ratio and constraints related to optical-fiber nonlinearities. Best noise performance is obtained with distributed amplification in which the transmission fiber is lightly doped with erbium and optically pumped, so that the gain just compensates the loss. Depending on the supervisory methods, amplified lightwave systems might be operated with regulated optical power or might be free-running, a choice that affects the signal power, efficiency, saturation, and noise figure of the fiber amplifier.
Crystal fiber amplifiers at 1.3 µm
Authors: Davis G. M. , Yokohama I. , Sudo S. , Kubodera K.
Published: February 2023

Experimental studies of potentially compact, high-gain, polarization-insensitive, low-noise crystalline fiber amplifiers for the important telecommunications wavelength of 1.3 µm will be reported for the first time. Crystalline hosts are attractive because they should provide higher gains per unit pump power than amorphous hosts,1 owing to their approximately 5-20 times narrower fluorescence spectra. Attaining high pump intensity along the length of the active medium is an even greater concern for practical amplifiers than for laser end pumped oscillators because much higher gains per unit pump power are required. The technology for fabricating suitable low-loss crystalline fiber waveguides is still in its infancy. Small diameter fibers of Nd:YAG were fabricated by means of laser- heated pedestal growth.2 Gains of 3.4 dB were obtained from a 16 /im diameter, 1 cm long, unclad Nd:YAG fiber pumped by 0.809 radiation from a 140 mW Ti:sapphire laser. Studies of the dependence of amplifier gain on fiber diameter confirmed a strong dependence of gain G on diameter D (G α D−1.7). Extrapolation of the results indicates that gains in excess of 30 dB could be achieved by reducing the fiber diameter to 4µm. We shall describe our investigations of techniques for reducing the effective diameter of these crystalline fibers.
Practical approach to determining n, k, and d of a growing film with an in situ ellipsometer
Authors: Savrda Steve , Himel Marc D. , Guenther Karl H. , Urban Frank K.
Published: February 2023

Ellipsometry measurements, when limited to a single angle and wavelength, yield only two parameters, V and A. This leaves us with an underspecified condition because we have three unknowns, n, k, and d. In the determination of the properties of a growing thin film, certain cases allow us to assume that one of the unknowns is either constant or is known from independent measurements. However, making measurements at multiple angles of incidence or wavelengthsis a choice we do not have when we use a single-wavelength Rudolph Research ellipsometer installed onto a Balzers coating chamber. For in situ investigations of the optical properties of low-voltage reactive ion-plated films, we cannot assume that n and k are known and constant, which makes data processing difficult and time consuming. For realistic modeling of thin-film growth from in situ ellipsometer measurements, we have included an interface layer between the substrate and the growing film. The computer algorithm that we use to determine the optical properties of this system relies on measurements taken at different film thicknesses. The accuracy of this method is determined by computer simulation of film growth in terms of the resulting ψ and Δ values.
Determination of the optical functions of transparent glasses using spectroscopic ellipsometry
Authors: Jellison G. E. , Sales B. C.
Published: February 2023

Two-channel spectroscopic polarization-modulation ellipsometry measurements have been made on four different glasses (a fused SiO2 glass, a fine-annealed BK-7 glass, an indium-lead-phosphate glass, and a germanium-arsenic-selenium glass). It is shown that this technique is sensitive to thin surface layers and that these surface layers can be modeled by using the Bruggeman effective-medium theory with 50% glass and 50% voids. If we correct the experimental spectra for this surface layer, the refractive index of the sample can be determined to ±0.002 in the transparent region. For wavelength regions where the material is normally opaque, the ellipsometric data can be corrected for this overlayer, thereby increasing the accuracy of the determination of both the refractive index and the extinction coefficient.
Neutral and color-selective beam-splitting assemblies with polarization-independent intensities
Authors: Ho F. C. , Dobrowolski J. A.
Published: February 2023

A device is described that makes use of three beam-splitting surfaces to produce four different beams, of which two have polarization-independent spectral-intensity distributions. If necessary, several such devices can be placed in series to produce more than two polarization-independent output beams. The devices can act over a wide spectral region, and they can be either achromatic or color selective. Multilayer coating designs, which result in beam splitters suitable for several different applications are presented. The angular behavior of such devices is investigated, and ways are suggested for reducing their variation with angle of incidence. The theoretical and measured performances of an experimentally produced device are compared.
Picosecond optical nonlinearities in InAs/GaAs short-period strained-layer superlattices
Authors: McCallum D. S. , Huang X. R. , Boggess Thomas F. , Dawson Martin D. , Smirl A. L. , Hasenberg T. C.
Published: February 2023

We report the observation of room-temperature optical nonlinearities near 970 nm in InAs/GaAs short-period strained-layersuperlattices (SPSLSs) grown by migration-enhanced epitaxy on GaAs substrates. A typical sample structure consists of six repetitions of two monolayers of InAs and five monolayers of GaAs; this sequence is followed by 25 nm of GaAs, and the entire structure is repeated 50 times. Room-temperature absorbance measurements show clearly resolved excitonic features, and time-resolved photoluminescence indicates a carrier lifetime approaching a nanosecond in these samples. Nonlinear transmission and degenerate four-wave mixing (DFWM) measurements were made with a synchronously mode-locked Styryl 13 dye laser, which produced pulses of 4 ps duration tunable over 950-990 nm. Strong bleaching of the n = 1 heavy-hole excitonic absorption and a large DFWM signal associated with this absorption change were observed. Specifically, a differential transmission (ΔT/T) of 0.43 was measured for a peak pump irradiance of approximately 35 MW/cm2. For the same excitation conditions, the DFWM diffraction efficiency was approximately 4 × 10-4. Measurements were made as a function of wavelength, time delay between the pumps and probe, and pump fluence for several distinct structures. The strengths of the nonlinearities and the carrier dynamics in the various structures will be discussed.
Self-focusing revisited: spatial solitons, light bullets, and soliton explosions
Authors: Silberberg Y. , Aitchison J. S. , Weiner A. M. , Leaird D. E. , Oliver M. K. , Jackel J. L. , Smith P. W. E.
Published: February 2023

Self-focusing is a subject that is almost as old as the field of nonlinear optics. Here we report on recent experiments at Bellcore that studied self-focusing in nonlinear planar glass waveguides. It is well known that self-trapping in an optical Kerr medium is unstable in three dimensions, but it is stable when diffraction is limited to one spatial dimension, such as in a planar waveguide. We have demonstrated that a beam that diffracts at low powers is self-trapped at high powers. The self-trapped beam can be described as a spatial soliton, a beam that retains its spatial profile as it propagates along the waveguide. We have also observed interactions between two bright spatial solitons. When the power levels are increased above those required to form the fundamental spatial solitons, we have observed the breakup of the beam shape into a triple-peak profile. This phenomenon is explained as the result of weak two-photon absorption in the waveguide. We will show through numerical modeling how two-photon absorption leads to the breakup of spatial and temporal solitons. The second part of the talk will take another look at three-dimensional self-focusing, a process that is known to be unstable and to lead to catastrophic collapse of the beam profile. We will show theoretically that in the presence of dispersion, a properly constructed pulse could undergo spatial-temporal collapse to generate extremely short and intense pulses of light. We will discuss the condition for such a process and the effects expected to limit it.
Interactions for two solitons in Raman-pumped fibers
Authors: Chi Sien , Wang Lee-Jyi
Published: February 2023

The interactions between two neighboring solitons in a bidirectional Raman-pumped fiber system is considered. We choose two different separations between two adjacent solitons and three different pumping periods to illustrate this work. For the separation equal to 10 times the soliton pulse width, the interaction between solitons is negligible. With the BPM simulation, the longest acceptable pumping period is about 20 km.
Harmonic production in strong-field electron-atom scattering*
Authors: Grobe R. , Lappas D. G. , Eberly J. H.
Published: February 2023

We present the numerical solution for the scattering of an electron by a one-dimensional atom model in the presence of a strong laser field. We investigate a regime in which the incoming electron wave packet is partially captured by the neutral atom. We computed the spectrum of the coherently scattered light from the time dependent dipole moment. The generated light contains frequencies which are odd as well as even integer multiples of the fundamental laser frequency. The presence of a bound state resonance dramatically enhances the generation of very high-order harmonics. We will comment on the close relationship between light spectra generated by the scattering process and those which are due to photodetachment.
Application of the triple-correlation technique to diffraction-limited imaging in the presence of unknown aberrations
Authors: Cho Doo Jin , Morris G. Michael
Published: February 2023

We describe a laboratory experiment that demonstrates diffraction-limited imaging in the presence of aberrations in the imaging system. It is well known that in stellar-speckle interferometry, short-exposure speckle images carry diffraction-limited information in spite of the presence of atmospheric turbulence and the aberration in the telescope. In our experiment a phase plate, which simulates the random phase fluctuation of atmospheric turbulence, is artificially introduced in the pupil plane of the imaging system. This phase plate serves to eliminate the effect of aberrations in the imaging lens. We use triple-correlation methods to recover the object from speckled images produced by random phase fluctuations and aberrations. The bispectrum, calculated from the measured image intensity, is averaged over an ensemble of realizations. From this averaged bispectrum, the object is recovered by using established techniques. As an application, we may use the triple-correlation technique to obtain the diffraction-limited images of the human retina.
Image recovery in adaptive-optics systems by deconvolution from the time-averaged point spread function
Authors: Coy Steve C. , Cochran Gregory M.
Published: February 2023

We have found a simple and easy technique that, on the basis of detailed computer simulation, appears to offer the possibility of near-diffraction-limited imaging with even relatively poor adaptive-optics systems. The time-averaged optical transfer functions of systems with wavefront sampling as coarse as three times the Fried coherence radius remain significant out to spatial frequencies near the classical diffraction limit, which allows for the possibility of image recovery by direct deconvolution. Using a computer simulation incorporating many of the relevant physical effects, we have tested the technique, and it seems to work surprisingly well. Further analysis is required to better map its practical obstacles and limitations, and we intend to test the technique against real data in the near future.
IR (0.9-2.6 µm) imaging spectrometer for ground-based planetary astronomy
Authors: Wang Shu-i , Gradie Jonathan C. , Ludeen Thomas F. , Bosel Jeffrey P.
Published: February 2023

We report on the development of a prototype multichannel infrared imaging spectrometer designed for ground-based planetary astronomy at a variety of astronomical observatories, namely the JPL Table Mountain Observatory and various telescopes at the Mauna Kea Observatory. The instrument is capable of sampling simultaneously the spectral region of 0.9 to 2.6 µm at a spectral resolution of 1% using a cooled (77K) optical bench, a concave holographic grating and a special order sorting filter to allow the acquisition of the full spectral range on a 128ö128 HgCdTe infrared detector array. The field of view of the spectrometer is 0.5 arcsec/pixel in mapping mode and designed to be 5 arcsec/pixel in spot mode. The innovative optical design has resulted in a small, transportable spectrometer, capable of remote operation. The novel design, which employs holographic optics, is applicable for any remote sensing imaging spectrometer where size and weight of the optical system is critical.
Imaging spectrometer for planetary surface science
Authors: Glavich Thomas A. , Hovland Larry E.
Published: February 2023

The human exploration of the solar system will include the construction of a manned base on Mars. There is a need for surveys of the surface-material resources and surface atmospheric conditions of several places on the planet, where the data is to be taken on a human, rather than global, scale. This paper describes some potential instrumentation, using newly available technology compatible with surface penetrators or other hard-lander implementations, for measuring the surface materials and atmosphere of Mars. An extremely rugged, small, lightweight, and thermally self-compensating camera optical system has been designed for microspacecraft applications. It is also ideal for a penetrator. Research in acousto-optical tunable filter (AOTF) technology and spectral data collection has matured sufficiently that we can consider the addition of a narrow-band, tunable filter to the camera, thus obtaining a low-cost, low-power, rugged imaging spectrometer. Detectors and control electronics have been miniaturized and can be mounted to survive hard landings. Software systems for data selection and analysis based on the hierarchical selection of spectral bands will decrease the amount of data to be uplinked to an amount that is compatible with penetrator technology.