bluuebunny/crossref_metadata_2025 huggingface dataset:
Aberrations of even orders in tilted component systems
Authors: Rogers John R.
Published: February 2023

It is widely known that the image of a tilted object (or equivalently, the image formed by a tilted optical component) suffers keystone (trapezoidal) and anamorphic distortions. Although these are often referred to as first-order distortions, keystone is predominantly second-order in the pupil and field coordinates, and both can vary over wide ranges as the pupil and image are transferred through the optical system. Any distortion in the object seen by a particular surface changes the field dependences of all the aberrations introduced by that surface. Similarly, any distortion of the pupil presented to a particular surface will change the pupil dependences of all the aberrations introduced by that surface. Since both anamorphic and keystone distortions are highly asymmetric, their effects are to cause asymmetric changes to the pupil and field dependences of all the aberrations. Recognition of the origin of these unusual aberrations suggests new surface types for the design of general systems.
Infrared laser-microwave double resonance spectroscopy with intense electric field
Authors: Tanaka Keiichi
Published: February 2023

Infrared laser-microwave double resonance spectroscopy with intense electric field was applied to several simple molecules. In this technique, a rovibrational transition is brought into resonance with a laser line by the high electric field, while microwaves corresponding to a rotational transition are simultaneously irradiated to detect the double resonance effect as a change in the absorption of laser light. It is essentially an indirect method for the detection of microwave transitions under the influence of the Stark field and provides precise electric properties as well as zero-field molecular constants.
Infrared-Infrared double resonance spectroscopy of formaldoxime: asymmetry and line shape effects
Authors: Devoy D. , Percival R. M. , Duxbury G.
Published: February 2023

CO2 lasers modulated with single sideband acoustooptic modulators1 have been used for Stark tuned sub-Doppler infrared-infrared double resonance spectroscopy of the 10-μm bands of formaldoxime, CH2NOH. Fourier transform and diode laser spectra of these bands have also been obtained. The observed double resonance signals show a wide range of behavior ranging from symmetric rotor type patterns to those showing the effects of molecular asymmetry. An investigation of the resolution limitations on the saturation signals imposed by the Stark cell optical system has been made. The data have been interpreted with the aid of a spectrum simulation program in which the effects of the modulation on the second derivative line shapes have been incorporated.2 A de tailed comparison of intensity and line shape behavior has been made and an interesting variation of the dipole moment change has been found.
Theory of retinoscopic and photoretinoscopic images
Authors: Howland Howard C.
Published: February 2023

Retinoscopy is perhaps the most widely used refractive technique anywhere; however the theory of the retinoscopic image has been largely neglected for the past half-century. New interest in the retinoscopic image has been kindled by modern photoretinoscopic techniques.
Eigenmodes of broad-area diode lasers
Authors: Hohimer J. P. , Hadley G. R. , Owyoung A.
Published: February 2023

Multistripe gain-guided diode lasers were developed to overcome filamentation problems which occur in conventional broad-area lasers. However, the use of quantum-well active regions in broad-area devices greatly reduces the tendency toward filamentation.1 With filamentation removed, the behavior of broad-area devices can be examined in an attempt to understand and better control the operation of these devices. While uniform near-field intensity profiles have been reported for short-pulse (≤500-ns) operation,2,3 multipeaked (multilateral transverse mode) behavior is observed for long-pulse and cw operation. We have modeled a 100-µm wide broad-area device operating cw near threshold and have compared the calculated eigenmodes with those observed in similar free-running devices. For long-pulse and cw operation, the presence of a real refractive-index profile across the broad active layer due to heating effects is shown to be important in determining the dominant lasing mode. We also present the results of injection seeding studies which allow us to selectively induce oscillation in a number of lower-gain modes which would otherwise not be observable.
Electrooptic modulation in an InGaAs/GaAs strained layer multiple quantum well structure
Authors: Van Eck T. E. , Chu P. , Chang W. S. C. , Wieder H. H.
Published: February 2023

GaAs/AlGaAs multiple quantum well structures have been studied extensively for applications in electrooptic modulation.1 One drawback of the GaAs/AlGaAs material system is the opacity of the GaAs substrate at the exciton absorption wavelength. This problem can be avoided with the InGaAs/GaAs material system because the exciton absorption energy is less than the GaAs band gap. Unlike AlGaAs, InGaAs is not lattice-matched to GaAs, but thin layers of InGaAs can be grown on GaAs with the lattice mismatch accommodated by strain rather than misfit dislocations. A device consisting of ten periods of 100-Å thick In0.13Ga0.87As quantum wells and 150-Å thick GaAs barriers was fabricated. The quantum wells are in the intrinsic region of a PIN diode so that a large, nearly uniform electric field can be applied. With zero applied bias there is a single sharp absorption peak at a wavelength of 950 nm. With increasing reverse bias the absorption peak rapidly collapses while shifting slightly to lower energy. With only 2 V applied to ten quantum wells, 6.4% intensity modulation is obtained at the peak wavelength. This rate of modulation per well is comparable with that reported for GaAs/AlGaAs quantum wells.1
Image compression application of a simultaneous Karhunen-Loeve transformation in space and color
Authors: Derrico Joel B. , Buchsbaum Gershon
Published: February 2023

Most color image coding techniques transform the primary color vectors, at each pixel, independently of their spatial arrangement. Since the spatial and chromatic dimensions of natural color images are not independent, efficient coding requires elimination of both spatial and chromatic correlation across chromatic bands. Global spatiochromatic decorrelation has not been utilized because of its enormous computational load.1 A more feasible local approach is presented which partitions a large image into subimages, where the computational load is reasonable. The subimages are transformed using the most significant eigenvectors generated by diagonalizing a model subimage covariance matrix found empirically by averaging subimage covariance matrices in a natural color image. These eigenvectors generate transformation masks that separate space and color information and form color image basis functions similar to mechanisms in the visual system. The masks are (i) achromatic, spatially oriented passing high spatial frequencies and (ii) color opponent, unoriented passing low spatial frequencies. By utilizing the cross correlation between space and color, this method achieves a high compression ratio (16:1) with good quality reconstruction without elaborate quantization techniques or variable word length coding.
Self-organization and spatiotemporal chaos in semiconductor laser arrays
Authors: Winful Herbert G.
Published: February 2023

We consider the spontaneous emergence of organized behavior and spatiotemporal chaos in an array of coupled semiconductor lasers. In the absence of coupling, each laser in the array exhibits a constant, steady state output intensity in response to a constant input pump current. The individual uncoupled lasers do not exhibit any interesting instabilities such as chaos. In the presence of coupling, the constant steady state can lose its stability with the result that nontrivial spatiotemporal complexity emerges. The nature of the spatiotemporal dynamics depends on the strength of the coupling between adjacent lasers. For low coupling strengths there is a stable steady state which is constant in time and in which the fields in adjacent elements have nearly equal amplitudes and a phase difference close to pi. As the coupling is increased a Hopf bifurcation to a spatially ordered and temporally periodic output is obtained. Further increases in coupling strength lead to full blown spatiotemporal chaos. For even larger coupling strengths we have observed an interesting intermittency featuring bursts of chaotic activity in the amplitudes. Associated with these bursts of chaos are discontinuous jumps in the relative phase. These phase jumps are organized in a steplike fashion in a manner reminiscent of a devil′s staircase.
Bulk semiconductor saturable absorber for a passively mode-locked NaCl color center laser
Authors: Soccolich Carl E. , Islam M. N.
Published: February 2023

We have passively mode-locked a NaCl color center laser to produce pulses with τ < 200 fs using bulk InGaAsP as a saturable absorber. In the first passively mode-locked NaCl color center laser InGaAs/InP multiple quantum wells1 were used as the saturable absorber. Our results simplify the material requirements for the saturable absorber and prove that passive mode locking does not require excitons or 2-D confinement provided by multiple quantum wells.
Does the optical design of intraocular lenses need improvement?
Authors: Pankratov Michail M.
Published: February 2023

The human eye has its best resolution in the fovea, which is located 4-8° off the optical axis. An intraocular lens (IOL) calculated with paraxial optics will thus have reduced performance in the fovea. Limits on the accuracy of the IOL placement lead to tilt and decentration, reducing the IOL performance in the fovea even further. Hence the IOL worst-case design should be optimized for a wide angle performance of at least ±12.5°. Rather than designing individual IOLs, a family of at least 5 IOLs for each power is designed with various combinations of the measured physical parameters of the eye: axial length, corneal curvature and asphericity, and anterior chamber depth. This allows the surgeon to select an IOL based on more than predicted IOL power alone.
Test colors
Authors: Van Trigt C.
Published: February 2023

Reflectance functions occurring in practice are usually smooth. We define as a measure of the smoothness of a reflectance function the square of its derivative integrated over the entire visual range. The problem: to determine for given tristimulus values the smoothest reflectance function in the sense above has sixteen types of solution related to the four types of optimal color in a way to be explained.
Discussion of MTF measurement of fiber optic face plates
Authors: Burger Robert J. , Carellas Peter
Published: February 2023

A process for measurement of modulation transfer function on fused fiber optic faceplates and other similar optical systems has been developed. The test technique quantifies the influences of fused fiber optic design parameters on imaging systems such as image intensifiers. Theoretical considerations regarding the effects of nonisoplanaticism, the required mathematical assumptions, and the modified test conditions for accurate and repeatable measurements are outlined and discussed. A commercial MTF measurement system utilized for traditional lens metrology was customized to be application specific to coherent fiber optic imaging systems. This paper also discusses measurements which illustrate some of the practical implications of the array structure of fused fiber optics in contrast to the resolution properties of aberration-free lens systems. Results from experiments are compared to some theoretical predictions.
Effect of atomic diffusion on laser dynamics
Authors: Narducci L. M. , Manka A. , Oppo G.-L. , Lugiato L. A. , Gao Jin Yue
Published: February 2023

The objective of this presentation is to discuss a simple model of laser in which the atoms can undergo diffusive motion and to characterize the main dynamic effects associated with this often ignored feature of theoretical models. For this purpose we reconsider a laser cavity with flat mirrors1 and special geometry that allows diffraction along only one of the transverse directions to the resonator axis. As already found in an earlier model, here we also show that low threshold instabilities can lead to a departure from the homogeneous stationary state, to the creation of complex spatial patterns, and to cooperative frequency locking, a state of operation in which several transverse modes can oscillate synchronously. There are significant differences, however, in the shape of the domains of instability and in details of the laser dynamics following the destabilization of the homogeneous state. In addition, for selected parameter values the operation of the laser may actually become more stable in the presence of atomic diffusion.
Timing and detuning studies of asynchronously pumped mode-locked dye laser
Authors: Jiang Shuanghua , Casperson Lee W. , Macfarlane Duncan L.
Published: February 2023

The synchronously pumped mode-locked (SPML) dye laser is one of the most efficient ways of producing tunable picosecond and subpicosecond optical pulses throughout the visible and near infrared. An issue of practical importance is the longterm stability associated with these devices, and of interest here is the specific timing relation between the pump pulse and the dye laser pulse. In this study we explore, experimentally and theoretically, this relationship for a rhodamine 6G SPML dye laser system. For positive detunings we have found an almost linear relationship between the occurrence time of the dye pulse and the cavity length detuning. Our semiclassical model works well in quantitatively predicting our experimental data.
Perception of self-motion from optical flow
Authors: Warren William H.
Published: February 2023

Gibson first showed that patterns of optical flow specify the direction of self-motion or heading. Recent experiments confirm this empirically: (1) During translation, observers perceive heading with 1° accuracy with as few as three dots, based on the radial structure of the flow pattern. Velocity field information is sufficient for such judgments and the visual system can tolerate large amounts of flow field noise. (2) During movement on a circular path, curvilinear heading is perceived with as few as two dots, based on the hyperbolic flow structure, although the velocity field is insufficient in this case. (3) Translational and rotational components of flow (e.g., during a pursuit eye movement) can be decomposed with as few as twelve dots—except in the special case of approach to a plane. Thus, observers rely on differential motion between elements separated in depth rather than a general solution.
Phase retrieval for objects having glints
Authors: Fienup J. R.
Published: February 2023

Reconstruction of a coherent (complex-valued) image of a general object from a single snapshot of Fourier (far field) laser intensity data is very difficult with existing algorithms. For the special case of an object having one or more glints (delta functions), a set of three algorithms, used in succession, has been demonstrated to be capable of reconstructing a high fidelity image. The first algorithm employs the component of the autocorrelation function (computed from the Fourier intensity) of the image due to the glints. It reconstructs the glints (complex values and positions) using a triple-intersection approach. The second algorithm is the AF synthesis (Baldwin-Warner) algorithm which, starting with the reconstructed glints and using the Fourier intensity data, reconstructs the remainder of the image, but with some residual artifacts. The third algorithm is the iterative Fourier transform algorithm which completes the reconstruction using both the Fourier intensity data and a support constraint (derived from the autocorrelation function). Performance of the approach is quantified as a function of glint strength and photon levels.
TIRM as a diagnostic tool for thin optical coatings
Authors: Carniglia C. K.
Published: February 2023

Total internal reflection microscopy (TIRM) has been shown to be a useful tool for the study of substrate surfaces.1 The surface under investigation is illuminated from within by a laser beam incident on the surface at an angle beyond the critical angle. A microscope focused on the surface collects only light scattered from substrate defects. TIRM can also be a sensitive detector of scatter from a coating on the substrate surface. This scatter may be related to the microstructure or surface roughness of the coating. The degree of scatter from the coating depends on the incident angle of the illuminating beam. A configuration is presented for a TIRM system which allows the incident angle to be varied without affecting the position of the beam on the sample. This arrangement is also independent of the focusing adjustment of the microscope and thus it can accommodate substrates of various thicknesses.
Infrared properties of iron oxide films
Authors: Apfel Joseph H.
Published: February 2023

The optical constants for iron oxide films have been obtained for the infrared spectral region by fitting the measured transmittance with a classical oscillator model.1,2 The primary lattice vibration bands were identified from the p-polarized transmittance at 45° of an 0.08-µm thick film on germanium as described by Berreman.3 The location, intensity, and width of three superposed oscillators were adjusted to agree with the lattice vibration bands that were observed. The model also requires the high frequency dielectric constant which was estimated from the refractive index in the near infrared region where the film is completely transparent. The oscillator model is shown to provide good prediction of the normal incidence transmittance of a 3.9-µm film on germanium. Both films were prepared by reactive evaporation of iron metal using an activated process known as plasma plating or ion plating.
Soliton switching in nonlinear fiber devices: theory and experiment
Authors: Doran N. J. , Blow K. J. , Nayar B. K.
Published: February 2023

Soliton effects have been proposed as a means of attaining high contrast, complete pulse effects in waveguide (probably fiber based) devices.1 We present the central concept which is that the integrity of solitons provides a nonlinear phase coherence (i.e., a nonlinear phase shift which applies throughout the pulse) thus allowing processing on the entire pulse in phase sensitive configurations. The generality of this concept is demonstrated by means of a simple but accurate model where the soliton phase is shown to be simply related to intensity and proportional to intensity. Examples of nonlinear interferometers in the Sagnac and Mach-Zehnder configurations are presented. The all-fiber realization of the Sagnac interferometer, the nonlinear optical loop mirror (NOLM), will emerge as a potentially useful device. In addition it is clearly shown that nonlinear directional couplers (e.g., twin cored fibers) fit in with the general concept. The simple model is shown to apply and conditions for achieving soliton switching are calculated. An experimental realization based on the NOLM is presented and results showing over 90% energy switching for subpicosecond pulses are displayed. Limitations imposed by the self-Raman effects are shown and an optimized configuration is presented.
Optical detection of surface acoustic waves using stationary holographic reference gratings
Authors: Black T. D. , Green M. , Larson D. A. , Torti R. G. , Wang Y. J.
Published: February 2023

Experiments using holographically recorded phase gratings in a proximity probing method for the optical detection of surface acoustic waves (SAW) have been performed. The interaction of a probing beam with a traveling SAW and a stationary reference grating (SRG) has been analyzed and experimentally verified previously.1,2 The detected intensity in the primary orders of diffraction is modulated at the fundamental SAW frequency. For the proximity case where the SRG is separated from the SAW by a distance L, the sensitivity of detection is dependent on the separation between the SRG and SAW as well as the characteristics of the probing beam. We outline the analysis of the probing technique and present our most recent experimental results using holographic reference gratings (HRG). The SAW were produced by an interdigital transducer on a LiNbCh substrate using fifth harmonic generation. The SAW frequency was ~87 MHz corresponding to a wavelength of 40 µm. The HRG were recorded in high resolution film emulsions on glass plates. The sinusoidal periodicities of ~41 µm were measured using a Tencor Alpha-step surface profilometer. The detected intensity modulation dependence on proximity, SAW detection sensitivities, and probing laser beam effects are reported.
Luminescence of wide bandgap II-VI compounds — past, present, and future
Authors: Shionoya Shigeo
Published: February 2023

Luminescence research of wide bandgap II-VI compounds such as ZnS, ZnSe, and CdS has a long history tracing back to the nineteenth century. The mechanism of luminescence of ZnS phosphors was elucidated in the late 1960s after much effort over a long period. The importance of ZnS phosphors as TV phosphors is rising more and more toward the realization of high definition TV. Recently the demand to obtain light emitting diodes and semiconductor lasers operating in the short-wavelength visible region has rapidly increased.
Site selective laser spectroscopy of defects in solids
Authors: Wright John C.
Published: February 2023

When crystals are doped with aliovalent ions, defects are formed to balance the charge mismatch. Many defect structures can form from different combinations of the dopant and charge compensating ions. Site selective spectroscopy can be used to selectively examine specific structures using fluorescent dopant ions whose crystal field splittings reflect the local environment. The fluorescence is used to measure absolute site concentrations, and follow the concentrations as the crystals are modified by changing dopants, concentrations, crystal temperature, or the partial pressure of equilibrating gases. The individual defect sites can be identified and the distribution of different defects can be described by models of the solid state chemistry. The dynamics of defect formation can also be followed to acquire a detailed microscopic description of the defects. Sites with particularly favorable optical properties (radiative transition rates, energy transfer, quantum efficiency, etc.) can be optimized by appropriate processing conditions.
Room temperature continuous operation of vertical cavity microlasers
Authors: Lee Y. H. , Jewell J. L. , Mccall S. L. , Walker S. J. , Scherer A. , Florez L. T. , Harbison J. P.
Published: February 2023

The microlaser structure has a top p-doped mirror, a full wave thick spacer with three InGaAs quantum wells, and an n-doped bottom mirror, all grown by molecular beam epitaxy. The structure was designed for 980 nm. Chemical beam ion-beam assisted etching was used to generate various sizes of square mesas (5, 10, 25, 50, 100, 200 µm). Deep (5-µm deep) and shallow (2.5-µm deep) etchings were tried and compared. Shallow etched samples generally showed better thermal and spectral characteristics. Pulsed threshold currents are the same for both. Continuous lasing was observed for 10- and 25-µm mesas with 4- and 13-mA current, respectively. In pulsed operation, the threshold currents are 2.0,4.0,10,30,120 mA for 5-, 10-, 25-, 50-, 100-µm mesas, respectively. For mesas smaller than 25 µm, the threshold current increases linearly with mesa linear dimension. This linear dependence is explained by a strong surface recombination for these small mesas. For the larger ones, the threshold current increases linearly with mesa area at 1.2 kA/cm2. With this current density and proper passivation of the side walls of the smaller mesas, one should achieve 300-µA threshold current for a 5-µm mesa. The maximum peak power was 86 mW from a 100-µm mesa at 980 nm.
Ferroelectric liquid crystal optical exchange switches
Authors: Robinson Michael G. , Johnson Kristina M. , Doroski David
Published: February 2023

Optical 2 × 2 exchange switches can be utilized as routing elements for optical computing and fiber optic based networking systems. Here we demonstrate a 2 × 2, polarization independent ferroelectric liquid crystal (FLC) optical exchange switch, which can be used for these applications. Based on the nematic liquid crystal switch of Wagner and Cheng,1 it operates by separating the input beam into two orthogonal polarizations with a polarizing beam splitter. The beams are then directed through a surface stabilized, parallely aligned FLC cell. By applying ±15 V across the cell the optical polarization is either switched or left unaltered. Using a further polarizing beam splitter, the beams are recombined to produce a single unpolarized beam; its direction is determined by whether the FLC was switched or not. Due to its symmetry, this device can operate as a 2 × 2 exchange switch. Preliminary measurements indicate switching speeds of <30 µs at ±15 V with <−16-dB crosstalk primarily as a result of the beam splitter performance. Device component specifications suggest an operational bandwidth of 30 nm either side of the designed wavelength. Better results are expected with faster FLC cells and improved beam splitters. Other novel total internally reflecting FLC switch designs are being investigated that are polarization independent and have extinction ratios similar to the device of Meadows et al.2
Cooperativity in the perception of surface shape and reflectance
Authors: Knill David C. , Kersten Daniel
Published: February 2023

The luminance pattern in an image is a function of several different scene characteristics. The primary ones are surface shape, surface reflectance, and the pattern of incident illumination. Faced with the task of generating and maintaining an accurate percept of these scene characteristics, our visual systems must somehow be able to parcel out the different causes to changes in image luminance. This requires some degree of interaction in the estimation of shape, reflectance, and illumination. We used two juxtaposed, equivalent luminance gradients as a stimulus for studying this interaction. When the stimulus appears flat, the perceived lightness of the two patterns is consistent with the assumption of a smooth illuminant over a step change in reflectance. This is not, however, the only plausible percept, as a similar luminance pattern can be generated by natural shading of two smoothly curved surfaces with equivalent reflectances. We added several different shape cues to the stimulus in support of the latter interpretation, including occluding contours, texture, and stereo, and studied their effect on perceived lightness.
Precision in the perceived speed of a moving plaid
Authors: Ferrera Vincent P. , Wilson Hugh R.
Published: February 2023

When two drifting cosine gratings with different orientations are superimposed they can form a coherently moving 2-D pattern (plaid). The resultant speed of such a pattern increases as the angle (θ) between the component directions becomes broader, provided that the speed of the components does not change. It has been reported that speed discrimination for moving plaids is limited by noise in the component speed signals.1 Thus, one would predict that speed discrimination for plaids would depend on component speed, but not on θ. We measured speed discrimination for both plaids and gratings using a 2AFC paradigm. We found that for plaids with slow moving components (drift rate =1.0 Hz), speed discrimination improves with increasing θ. For example, we found that speed discrimination Weber fractions (ΔV/V) for a grating drifting at 1.0 Hz were around 20%, but decreased to 12% for a plaid with 1.0-Hz components and θ = ±75°. In this case, the speed of the plaid was four times the speed of the components, however, speed discrimination was not as good as for a 4.0-Hz grating (ΔV/V = 6%). It is still possible to account for these results based on component speed uncertainty because, when component uncertainty is propagated through a transformation such as the intersection-of-constraints, the variance in the resultant does not increase as fast as its mean speed. Therefore, the Weber fraction for discriminating the speed of the resultant may decrease by a factor of √2.
Stimulated Brillouin scattering gain variation and transient effect in a CH4:He binary gas mixture
Authors: Jones D. C. , Mangir M. S. , Rockwell D. A. , White J. O.
Published: February 2023

Competition between stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) is common in many substances. Because the steady state Brillouin gain is often larger than the steady state Raman gain, particularly at higher densities of the medium, the SRS process usually dominates only in a regime in which transient effects reduce the SBS gain significantly below its steady state value. The objective of the present work was to determine the extent to which the nature of the SBS/SRS competition in methane gas could be affected not by adjusting the temporal characteristics of the pump laser, but by adding a second gas such as helium. Our experimental results show that the SBS gain reduction can be substantial and is manifested in two ways. First, the SBS threshold systematically increases by as much as a factor of 2 with increasing helium partial pressure. Second, SRS becomes the dominant process at the highest pump energies studied. The data are consistent with a transient gain model in which the effect of the helium is to increase the Brillouin linewidth. This broadening most likely results from increases in any of several transport coefficients (the viscosity, thermal conductivity, and the mass diffusion constant) or the enhancement of relaxation effects.
Scattering of transverse magnetic waves with a nonlinear film
Authors: Leung K. M. , Lin Lida
Published: February 2023

Analytical results have been obtained for the scattering of transverse magnetic waves with a nonlinear film, in particular when the change in the dielectric constant is small.
Optical generation of picosecond electrical pulses in asymmetric quantum well structures placed in transverse magnetic field
Authors: Khurgin J.
Published: February 2023

It has been shown1 that when a magnetic field is applied to the asymmetric quantum well (QW) structure in a direction perpendicular to the direction of growth, the transverse dispersion curves of the energy subbands in the conduction and valence bands shift by an amount proportional to the field strength and to the displacement of the center of gravity of the subband envelope function. It is shown in this work that optically excited carriers have asymmetrical distribution in k vector space and therefore they have finite drift velocity in the direction perpendicular to both growth direction and field direction. Depending on whether the external circuit is open or closed, that results in either voltage along the QW plane or the current in that direction. When the optical pulse is off, the voltage (current) decays with the time constant equal to that of intraband relaxation time, i.e., of the order of 1 ps or less depending on temperature. This may serve as a basis for future ultrafast detectors or as a tool for generation and study of hot carriers. Current sensitivity of the proposed device has been evaluated as a function of material, geometry, field, and other factors and found to be of the order of a few μA/W at 10-T magnetic fields.
Optimum design of the coupling circuit for a 1.3-μm LD using a hemispherical-end single-mode fiber
Authors: Tachikawa Yoshiaki , Nishi Isao
Published: February 2023

A coupling circuit for a 1.3-μm wave length InGaAsP/InP laser diode (LD) with a hemispherical-end single-mode fiber has been optimized to attain low coupling loss and to suppress influence of optical feedback from fiber input and output endfaces. As a result, a low coupling loss of 2.4 dB was achieved experimentally by using a polished hemispherical fiber end with curvature radius of 10 μm. For conventional Fabry-Perot (F.P.) LDs with external feedback from the hemispheric endface, output power variations of 0.3-0.6 dB and longitudinal mode hopping of 0.8 nm occurred when the external cavity length was varied by a quarter wavelength of the laser light. The output power fluctuation tended to enlarge in automatic power control (APC) conditions. By applying antireflection coating with reflectivity of −30 dB to the hemispherical endfaces, power fluctuation was sufficiently reduced, even in the APC condition. These external cavity effects may also occur in distributed feedback (DFB) LDs. However, mode hopping due to external feedback was not observed experimentally for the DFB LDs. An intensity noise, due to external feedback from the fiber output endface, was also serious for both types of LD when operating above threshold. Peak noise was reduced more than 20 dB by decreasing the reflectivity of the fiber output endface to less than −40 dB by using matching fluid.
Ultrafast all-optical gates based on soliton trapping in fibers
Authors: Islam M. N.
Published: February 2023

Ultrafast, all-optical soliton trapping logic gates including an inverter, exclusive- OR, and AND are experimentally demonstrated in birefringent fibers. The soliton trapping local gates are three terminal devices with orthogonally polarized inputs, phase-insensitive nonlinear operation, and switching energies of ~42 pJ. The experimental apparatus consists of a 20-m length of highly birefringent optical fiber followed by a frequency bandpass filter. Using a filter with an ~0.2-THz bandpass, the contrast for the exclusive-OR is 8:1, but the output pulses are about 10× broader than the input pulse width. We show a cascadable inverter with an ~4:1 contrast ratio by widening the filter bandpass so the output pulses can propagate as solitons in a fiber. A 4:1 contrast ratio is sufficient for distinguishing between solitons and dispersive waves in fibers, and the reshaping properties of solitons contribute to logic level restoration.
Photoinduced absorption in photorefractive barium titanate
Authors: Brost G. A. , Motes R. A.
Published: February 2023

The photorefractive properties of barium titanate are influenced by the presence of secondary photorefractive centers. The consequence is an intensity-dependent photorefractive effort due to changes in the effective empty trap concentration. Information about these centers can be obtained by studying the photo-induced absorption. We have measured the spectral and temporal characteristics of the intensity-dependent absorption induced in barium titanate by illumination with argon laser light. The absorption spectrum consists of a fast (millisecond) and a slow (seconds) component, with absorption peaks in the visible and near infrared. We discuss possible sources for this absorption and the effects on the photorefractive properties.
Nonlinear propagation of laser beams in thin film and bulk ZnSe
Authors: Swartzlander G. A. , Ding Y. J. , Khurgin J. B. , Kaplan A. E.
Published: February 2023

ZnSe has been shown to exhibit strong nonlinear absorption for bulk and epitaxially grown samples1 due to bandfilling and coulomb screening. Consequently, one can expect very strong self-action effects, which, in turn, may be used to determine the nonlinear refractive index Δn(I, λ) (Ref. 2) as function of both the laser intensity I and the wavelength λ, using either self- focusing2 or self-bending.3 In this experiment we used a 10-ns pulsed dye laser beam with λ ~ 450 nm and intensities up to ~10 MW cm−2 to achieve these self-action effects. Bulk and epitaxially grown (on GaAs) films4 with thicknesses of ~500 and ~1 μm, respectively, were used, and the samples were cooled to 77 K. The laser beam was focused onto the sample. The spatial intensity distribution in the far field area displayed strong self-focusing and self-bending, which were measured and used to determine Δn(I, λ). These two methods for obtaining the nonlinear refractive index give qualitatively consistent results. In bulk ZnSe at λ ≈ 450 nm we observe the onset of self-action effects at I ≈ 300 kW / cm2. In the nonlinear case, a sharp band edge with a width of ~1.8 nm (corresponding to roughly kT) was measured, which we attribute to the saturation of the band-edge tail, i.e., bandfilling effects. In addition to self-focusing and self-bending, the large nonlinear refractive index of this material enabled us to demonstrate other nonlinear propagation effects.
Nonlinear optical studies of semiorganic crystals
Authors: Chang Tallis Y. , Ewbank M. D. , Vazquez R. A. , Warren L. F. , Newman P. R.
Published: February 2023

We invoke the term semiorganic to describe a new class of nonlinear optical compounds composed of part organic and part inorganic constituents. The recently reported crystal 1-arginine phosphate (LAP) is one such material where organic 1-arginine molecules form cations and crystallize with inorganic phosphate anions.1 We present another type of semiorganic crystal where organic molecules attach as ligands to the inorganic metal salt. We have grown two semiorganic crystals: zinc tris (thiourea) sulfate [Zn(TU)3SO4]2 and (4-nitropyri- dine-N-oxide) mercury chloride [(NPO)HgCl2]. Good optical quality crystals were grown by slow evaporation from solution with dimensions typically ~5 mm on a side. We have carried out nonlinear optical characterization of these materials using degenerate four-wave mixing experiments with a doubled Q-switched Nd:YAG laser (λ = 532 nm) to determine the magnitude of the third-order nonlinear susceptibility x(3). The preliminary results indicate that cobalt doped Zn(TU)3SO4 has a X(3) of about twice that of CS2. We have also observed a significant four-wave mixing signal in (NPO)HgCl2. Both of these crystals show relatively high damage thresholds of up to 17 J/cm2 with 8-ns pulses. Finally, we note that semiorganic crystals have great potential as nonlinear optical materials compared with organic crystals due to their ease of growth to relatively large dimensions, superior mechanical and thermal properties, high optical quality, and high damage thresholds.
Dopant effects on the growth of new nonlinear crystal: 2-(N-(L)-prolinol)-5-nitropyridine (PNP)
Authors: Lin J. T. , Wang W. S.
Published: February 2023

PNP was first proposed as a potentially interesting nonlinear optical crystal by Twieg and Dirk.1 They reported second- harmonic efficiencies of powdered materials of the order of 160 X urea. But so far, only small (≃0.2- × 0.2- X 0.3-mm3) single crystals of PNP have been grown. Furthermore, the solubility of PNP is too high from isooctane and toluene. In view of the above, PNP warranted a further detailed study. For PNP single crystals to grow and for investigation of nonlinear optical properties in technology, we must first choose suitable solvents and techniques for single crystal growth in bulk. In the present report, the dopant effects on habit of PNP single crystals are studied. We have made an attempt at Nd3+, Cd2+, Al3+, Pr3+, and a mixture of Nd3+ and Cd2+ doping into the solution of PNP. Nd:PNP and Cd:PNP certainly provide single crystals as good as can be obtained. It is assumed that Nd3+ solvents influence the mechanism of the growth, giving rise to the formation of less growth defects. Increasing solubility thus will lead to increased growth rate unless other factors interfere with this process.
Single Mode 500 mW Buried Heterostructure GaAs/GaAlAs Laser
Authors: Ungar Jeffrey E. , Bar-Chaim Nadav , Mazed M. A. , Mittelstein Michael , Oh Se , Ury Israel
Published: February 2023

The output power of GaAs/GaAlAs lasers with a buried heterostructure wave-guide designed to guarantee single mode operation has been increased above 500 mW in continuous operation at room temperature. To achieve the high output power, "window" technology has been employed which removes the active region from the facet and minimizes losses and catastrophic damage. In addition, the narrow buried heterostructure is flared at one end, adiabatically expanding the beam near the output facet. The cleaved facets are high reflectivity/low reflectivity coated to reduce the intensity at the back side of the laser in favor of higher output power. To manage the heat load of high power operation, a 1 mm long cavity is used. The vertical structure is a conventional double heterostructure grown by metal-organic-chemical vapor deposition (MOCVD). An output power exceeding 300 mW is achieved with chips mounted junction side up on copper heat sinks. Using a diamond as a heat spreader for junction side down mounting resulted in 500 mW continuous output power at room temperature. The introduction of the flare smoothed the far field pattern and reduced its width to one half. The full width at half maximum is 18° at peak power, close to the expected value for the expanded fundamental mode of the waveguide. This work was supported by the Defense Advanced Research Projects Agency and the Naval Research Laboratory under contract N00014-88-C-2099.
Higher-order analysis of the interference patterns in cross-grating interferometers
Authors: Cheng Yih-Shyang
Published: February 2023

Both the on-axis and off-axis four-beam, interference patterns are analyzed using ray tracing. The cross-gratinglike interference pattern is accompanied by an extra term which consists of two orthogonal two-beam interference patterns. When partially coherent light is used, the extra term generally degrades the contrast of the cross-gratinglike pattern unless some special kinds of source are utilized. With gratings of high spatial frequencies, the amplitude of the extra term can become large compared with the desired term. In consequence, the localized cross-gratinglike pattern is changed to be periodic in different directions.
Interferometric angle encoder
Authors: Mertz Lawrence
Published: February 2023

A pair of parallel mirrors that fold the beams of a Michelson interferometer serve as the mobile rotor of an angle encoder. The device remains in interferometric alignment for severe perturbations to all six degrees of freedom of the rotor and the path difference is purely a function of one angle that has a physical range of a third of a radian. For a 12-cm spacing of the parallel mirrors, a He-Ne laser produces a million fringes per radian. The interferometer conveniently adapts to a lenticular receiver giving three phase fringe signals suitable for a hexflash phase analyzer that provides a raw resolution of 1/1536 fringe (i.e., 650-prad rotor motion) with submicrosecond sampling time allowing good slew capability. A digital polar innovation filter unwraps and averages the samples in real time to maintain an extensive fringe count with even finer resolution.
Imaging of neutral atomic beams
Authors: Sheehy B. , Shang S.-Q. , Metcalf Harold J. , Hatamian S.
Published: February 2023

We have developed a method to image a beam of neutral atoms (chiefly usable for alkalis) that is essentially an extension to two dimensions of the usual hot wire method of detection. The beam of neutral atoms first passes through a a highly transparent, positively charged grid and then impinges on a heated grid of electroformed nickel with lower transparency and at ground potential. Atoms with ionization potential less than the work function of Ni that strike the heated grid are ionized at its surface and are then pushed through it by the 250-V/cm field produced by the voltage on the first grid. The ions are then accelerated through ~700 V to a pair of multichannel plates (MCPs) ~3 mm away where the single charged ion signal is amplified. The output electrons from the MCPs are accelerated by 1.7 kV to a phosphor screen ~3 mm away that glows when the electrons strike it. The phosphor screen is viewed by a TV camera whose output goes to a frame processor in a PC. The system has been used for studying transverse laser cooling (optical collimation) of a Rb beam done with diode lasers.
Production of slow atoms from a moving drop
Authors: Harvey K. C.
Published: February 2023

High densities of low velocity atoms or molecules may be produced from moving liquid drops. This technique can be useful for filling to high density neutral atom traps that have small well depths. If a drop travels at or near the mean thermal velocity of the atoms that are evaporating from the surface of the drop, the atoms that evaporate in the direction opposite the velocity of the drop have a velocity in the laboratory reference frame greatly reduced by the motion of the drop. These slow atoms may be further cooled in the trap by laser radiation. If the drop is rapidly heated by a laser pulse, the velocity distribution is compressed and the density of the low velocity atoms can be increased. Also the velocity distributions of the atoms evaporating from small drops may be interrogated by their Doppler-shifted resonance lines. This may give new information about liquids with small dimensions.
Computer simulation of partially coherent imaging by outer-product expansions
Authors: Van Der Gracht Joseph , Rhodes William T.
Published: February 2023

The simulation of 2-D quasimonochromatic partially coherent imaging and spatial filtering systems is computationally intensive. One approach separates the effects of the object from the system. A 4-D function that fully describes the effects of the source and pupil can be calculated, stored, and subsequently applied to as many different objects as desired. This method may be useful if a large number of objects are to be examined for a given source and pupil. The calculation of the 4-D function, referred to here as the C-function, generally requires the evaluation of a triple correlation and is numerically intensive. Previous workers have devised numerical algorithms that exploit properties of specific source and pupil shapes, such as circular symmetry, to reduce the computational load. We employ singular value outer- product decompositions on the 2-D sources and pupils, effectively reducing the problem to the analysis of a number of 1-D systems. The C-functions for 1-D systems are functions of two variables. Each 1-D source component interacts with every pupil component to yield these reduced-dimension C-functions. The 4-D C-function of interest is obtained by a sum of outer products of these 2-D C-functions. If the effective ranks of the matrices representing the source and pupil are sufficiently small, this approach can be computationally efficient.
Image enhancement by nonlinear optical signal processing
Authors: Javidi Bahram , Ruiz Jack , Ruiz Carol
Published: February 2023

Recently, we have described a multifunction nonlinear joint transform processor that can perform various types of operation such as image deconvolution and nonlinear correlation.1 The processing function for the specific operation is displayed at the input plane side by side to the input signal. Nonlinear transformations are applied to the joint power spectrum to produce the desired operation.
Novel diode pumped lasers
Authors: Fan T. Y.
Published: February 2023

Interest in diode laser pumped solid state lasers has increased dramatically in the past few years due to their advantages over lamp pumped devices and improvements in diode lasers. This has led not only to better performance for 1.06- and 1.32-µm Nd doped lasers, but also to demonstration of a number of novel diode pumped devices. This tutorial presents a survey of these novel lasers and emphasizes an understanding of the basic physics behind device operation.