bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical neural Al processing for binary pattern classification
Authors: Gustafson Steven C. , Little Gordon R.
Published: February 2023

This paper discusses computer simulations and experimental designs for assessing the binary pattern classification capabilities of basic types of optical neural Al processor. After learning binary input patterns whose binary class is known, these processors classify patterns whose class is unknown. This classification task may be difficult if the relationship between pattern and class has no concise statement or algorithm, as in the case of random problems.1
Simple method for colorimetric calibration of color television displays
Authors: Mulligan Jeffrey B.
Published: February 2023

Accurate colorimetric calibration of color monitors is best done by making spectrophotometric measurements. Instruments capable of making these measurements, however, are costly, often exceeding the cost of the computer and graphics controller. It is, therefore, desirable to have a technique for determining the chromaticities of the monitor primaries which does not require detailed spectral information.
New radiation frequency in tree-electron lasers with an axial guide field
Authors: Bali L. M. , Pandya T. P. , Jha Pallavi
Published: February 2023

Free-electron lasers with an axial guide field have been extensively studied. Freund et al.1have discussed the single-particle trajectories and calculated small signal gain. These studies, based on perturbative solutions of electron equations of motion, seem to have neglected part of the contributions of the guide field to the overall axial oscillations and the transverse oscillations of the electrons bulk flow through the cavity. On taking these into account, we find that new radiation frequencies appear. From single-particle dynamics or through solutions of Vlasov-Maxwell equations it is found that small axial oscillations of the electron equilibrium distribution give rise to a loss (or gain) at an additional radiation frequency

~
2

ω
b

γ
0
2

in addition to that at

2

ω
0

β
0

γ
0
2

reported earlier; ω
b
is the Larmor frequency of electron of energy γ0mc2, velocity β0cis due to the axial magnetic field, and ω0is the wiggler frequency. Significantly a three times bigger gain (or loss) is noticed at the same frequency

~
2

ω
b

γ
0
2

due to the transverse oscillations of the electron equilibrium distribution. These two terms combine to give a net gain (or loss) at the new frequency.
Novel behavior of a synchronously pumped femtosecond antiresonant ring dye laser
Authors: Lotshaw William T. , McMorrow Dale , Dickson T. , Kenney-Wallace Geraldine A.
Published: February 2023

A modified version of an antiresonant ring dye laser, which includes a dispersion compensating a four-prism sequence and longer (10-cm radius) focusing optics at the gain medium (rhodamine 6G), has a complex pulse width dependence on the dye laser cavity length. The dye laser, which is synchronously pumped by the second harmonic of a cw mode-locked Nd:YAG laser, yields short (<150-fs FWHM) pulses at two distinct cavity lengths.
Study of the Ne (6328-Å) laser with an unstable cavity
Authors: Chen T. J. , Huang Xian-Ling , Qin Yi-Jun , You Jiang-Nan
Published: February 2023

A Ne (6328-Å) laser with an unstable cavity has been made. It lases over a wide range in the unstable region. The computation shows that the eigenwaves exist in the asymmetric confocal cavities which have an aperture inside at the confocal plane. The distribution of E is only the function of the magnification β and Fresnel number N. The loss δ depends on both β and N; for the case of N = 0.80 and β = −1.02, the loss δ = 0.9% which is acceptable with a Ne laser. The high-order transverse modes also exist. For a general negative unstable cavity with an inside aperture at one of the conjugate image points, there is an equivalent asymmetric cavity having the same β and Was the general case. These two cavities have the same E distribution and loss (E up to a phase factor).
Domain of the third-order theory of a detuned inhomogeneously broadened laser
Authors: Christian W. R. , Mandel Leonard
Published: February 2023

The domain of the third-order theory of the single-mode laser is usually defined by the condition nB/A ≪ 1, where n is the photon number in the cavity, and A and B are the gain and saturation coefficients. When the laser cavity is detuned from line center by Δω ≡ ηγ, where γ is the natural linewidth of the atomic transition, A and B change in the prescribed manner given by the Lamb theory, and it is usually taken for granted that the theory is valid both for small and large detunings η. By examining the relationships between various parameters we show that the limits on the domain of the third-order laser theory effectively limit the allowed detuning in many common lasers to one natural linewidth (η ≈ 1).
Comparison of graphic techniques to aid optical thin-film Interference design
Authors: Smith Douglas J.
Published: February 2023

Prior to the extensive use of computers to calculate the theoretical performance of optical thin films, designers relied on graphic techniques to obtain solutions to specific problems. Now, with the advent of inexpensive computers, graphic techniques remain useful to gain insight into design performance and as a pedagogical aid. Several exact and approximate techniques which have previously been described1,2 are reviewed including the Smith chart, reflectance and admittance circle diagrams, and vector diagrams. The use of each technique is compared for high- and low-reflectance designs and advantages of each technique for various types of coating are discussed.
Thermooptical modeling of multilayer optical thin films subjected to laser irradiation
Authors: Bovard B. G. , Macleod H. A.
Published: February 2023

Thermally induced bistability observed experimentally in zinc sulfide and zinc selenide Fabry-Perot etalons1 has triggered our interest in the dynamic interaction of irradiance, temperature, and the optical properties of interference filters. Linder sufficient power, residual absorption in di electric materials can give rise to internal heating, changing the refractive indices. We have developed a model that considers the time dependence of the coupling between optical property and heat flow equations through the temperature dependence of the optical constants. During each time increment, the internal field inside a multilayer stack is calculated, and the losses in the Poynting vector determine the heat distribution map accordingly. Heat flow equations allow us to derive the corresponding temperature map, the new optical constants of the various materials, and the new values of the optical properties for the next iteration. This simulation follows dynamically the evolution of transmittance, reflectance, and electric field as a function of time, giving temperature and refractive-index maps. Electric-field dependence of the refractive index can also be included to model interference filters involving nonlinear materials.
Scattering vs wavelength from multilayer coatings: influence of cross-correlation laws
Authors: Amra C. , Grezes-Besset C. , Pelletier E.
Published: February 2023

We have shown how it is possible to characterize an optical surface by means of measurements of the scattered-light distribution. In the case of a multilayer coating, some particular techniques (Al layer, antiscattering effect) enabled us to determine the roughness of each interface and to solve the difficult problem of the cross-correlation laws inside the stack. We are now dealing with the variations of scattering vs wavelength, and we show that the total integrated scattering is strongly dependent on the reflection and transmission windows of the coatings. Such variations are directly connected with the cross-correlation laws between the interfaces, which is important information in determining these laws and, therefore, characterizing the microstructure of materials in thin-film forms.
Spectral mechanisms for increment detection in the perifoveal retina
Authors: Buck Steven L. , Knight Roger
Published: February 2023

We are studying detection mechanisms to generate and evaluate models of postreceptoral channels in extrafoveal human vision. Stiles and others have described spectral (pi) mechanisms that mediate increment detection in prescribed conditions in the fovea. These mechanisms are characterized in part by their test-spectral-sensitivity (TSS) functions. We have begun to measure TSS functions at 7° eccentricity (nasal retina) as the spectral, spatial, and temporal characteristics of the test and background stimuli are varied to characterize the full range of detection mechanisms that operate in the perifoveal retina.
Temporal summation for color and brightness thresholds
Authors: Nagy Allen L.
Published: February 2023

Threshold-vs-duration curves for achromatic and chromatic thresholds were measured in the dark-adapted state and on a large bright white background. Observers viewed a continuous green (546-nm) stimulus field fixed at a luminance level slightly above threshold in both adaptation conditions so that it had little effect on the adaptation state of the observer. The stimulus field was either 10 or 75 min in diameter. Either the brightness or the color of the field could be changed briefly.
Noise performance of GaAs optoelectronic integrated receivers
Authors: Sasaki Masaru , Oikawa Y. , Horimatsu Tetsuo , Touge T. , Makiuchi M.
Published: February 2023

Optoelectronic integrated circuit (OEIC) technology is expected to be used not only in optical communications but also in optical interconnections and optical computing.
Foveal dark adaptation with small flickering test stimuli
Authors: Eisner Alvin
Published: February 2023

Sensitivity to an 18-Hz 20-min of arc test stimulus following a 5-min duration bleach depends on the spectral characteristics of both the bleach and test. When the test stimulus is 656 nm and the bleach is ~60,000 to 70,000 td, equating different wavelength bleaches for L cone quantum absorption causes dark adaptation curves to be identical or similar. Conversely, varying the test wave length following a 660-nm bleach causes profound differences in the shapes of the dark adaptation curves. When the test is 656 nm, sensitivity drops by ~1.8 log unit within ~30 s or less at ~3 min or later after extinction of the bleach. When the test is 540 (one subject) or 470 nm (another subject), sensitivity drops by ~0.7 log unit within ~40 s or less ~1 min or less after extinction of the bleach. When the test is 600 nm, sensitivity decreases gradually by ~1.0 log unit over a span of 10 min or more. To minimize rod-cone lateral interactions, dark adaptation curves were in all cases obtained in the presence of 480-nm annular surrounds (1° i.d.), which followed bleaches of at least 30,000-scotopic td illuminance.
Independence of color and form in binocular rivalry in the periphery
Authors: Wolfe Jeremy M.
Published: February 2023

Most information about eye dominance and bin ocular rivalry comes from studies using foveal stimuli. In the present experiments, we measured dominance in a rivalry task at thirty-five locations in a 20 × 15° field. To assess dominance, dichoptic stimuli were presented at one location for 250 ms. Three pairs of stimuli were used: vertical vs horizontal, left oblique vs right oblique, red vs green. Each pair was presented forty times at each location. Subjects gave a forced choice response to indicate which stimulus was most clearly visible on each trial. For each stimulus pair, some spatial locations were dominated by the left eye and others by the right. Repeatable idio-syncratic spatial distributions of dominance were found. Foveal eye dominance did not predict dominance elsewhere in the visual fields of normal subjects. Within a subject, vertical vs horizontal results were significantly correlated with oblique results (p < 0.05). However, the same results were not significantly correlated with the results for color rivalry. These results suggest that eye dominance is a measure of foveal dominance. They give further support to the hypothesis that color and form are processed somewhat independently in the visual system.
Invariant principal components for pattern recognition
Authors: Jouan Alexandre , Arsenault Henri H.
Published: February 2023

Methods for rotation-invariant pattern recognition using matched filters can be based on recognizing some invariant feature from the object of interest. Various techniques using circular harmonic components as the invariant features have been proposed. A new approach introduced here is to find a set of angular principal components q
k
(θ) for the object of interest f(r, θ). The principal components q
k
(θ) are found by defining vectors v
rk
(θ) which are the values along constant radii r
k
of the object and finding their principal components. Matched filters derived from those principal components may be used for pattern recognition that is invariant under rotations and changes of scale. If the object itself is used as the input to the filter, the scale invariance does not function well. Scale invariance is obtained when the projection of the object on the eigenvectors is used as the input to the principal component matched filter. This avoids calculation of the principal components for each target of interest, a much more time-consuming task than calculating the projections. Experimental results are shown.
Orientation sorting by diffraction pattern sampling
Authors: Venable Dennis L. , George Nicholas
Published: February 2023

Diffraction pattern sampling has been successfully applied to various problems in automatic pattern recognition, e.g., sorting of photographs based on scene content. In the current research we address the problem of sorting pictorial imagery according to whether a photograph was exposed upright (0°) or rotated 90°. This problem is of interest in the field of photographic processing, where along a continuous film strip, it is desirable to know whether a photograph was exposed in landscape or portrait mode. We limit the photographs in our study to those containing (1) landscape and houses only, (2) people only, and finally (3) groupings of houses and people. The optical transform is known to be independent of image translation but relates in a one-to-one fashion with image rotation. The detector used for sampling the optical transform is the Ring-Wedge detector, consisting of 32 wedge-shaped detectors and 32 concentric half-ring detectors. Using a feature set extracted from data obtained from wedge (angle-dependent) values, we illustrate the method of software development. Algorithms based on physical optics expectations are found to give reliable sorting in some cases. Discriminant functions using multiple feature algorithms are described. Results are presented in truth-table form for the three groupings listed above.
Integrated optical anisotropic waveguides: cutoff conditions and anisotropy-based devices
Authors: Knoesen A. , Gaylord Thomas K.
Published: February 2023

Dielectric planar waveguides are essential components in integrated optical devices, circuits, and systems. These waveguides are typically fabricated in anisotropic materials such as lithium niobate. Furthermore, the anisotropic nature of the waveguides is usually ignored due to the complexity of the analysis required to include these effects. In the present work, the allowed hybrid guided modes in anisotropic planar waveguides are calculated electromagnetically rigorously (without approximations). Three types of mode are identified: (1) homogeneous pure guided modes; (2) inhomogeneous pure guided modes; and (3) leaky guided modes. Furthermore, within these three types, there can be unconditionally stable and critically stable modes. Cutoff can occur starting from either of these latter two types through a transition to either a leaky guided mode or a leaky unguided wave. The cutoff conditions for these transitions are quantified. Active and passive cutoff anisotropy-based devices can be constructed simply by changing the direction of propagation on the anisotropic substrate. Polarizers, filters, and temperature sensors (performing an absolute rather than a differential measurement) are described that can be constructed in very simple configurations using the anisotropic propagation characteristics.
Nonlinear distributed feedback gratings
Authors: Rochford K. , Zanoni Raymond , Seaton Colin T. , Stegeman George I. , Assanto G.
Published: February 2023

Nonlinear distributed feedback gratings (DFBGs) hold considerable promise for application as fast all-optical data processing elements.1 The fabrication of practical nonlinear DFBG devices requires a careful study of the fabrication parameters which influence the performance. Using coupled-mode theory we characterize the device performance in terms of its bistable operation. Absorption, detuning, taper, and chirp are included in the model. The presence of absorption tends to diminish the nonlinear response but can be compensated for by a careful choice of operating wavelength, i.e., introducing appropriate detuning.2 Taper and chirp in the corrugation contribute to some interesting DFBG features, allowing for improvements of some figures of merit.
Electrophysiological and psychophysical tests of age-related changes in vision
Authors: Van Orden Karl , Sturr Joseph F.
Published: February 2023

There is evidence from the psychophysical literature which suggests that low spatial frequency-high temporal frequency visual input is distinctly impaired in older observers. We are investigating these changes by measuring evoked potential amplitudes elicited by gratings of 0.6 and 6 cycles/deg flickered at 15 and 7.5 Hz, respectively, presented at a variety of contrasts. Three groups of subjects (young, middle-aged, and older) were composed of ten males each. The slope of the function relating VEP amplitude to stimulus contrast provides an index of visual system gain at low grating contrasts and serves as the dependent measure of the study. The psychophysical method of magnitude estimation is being employed as well to determine if age related changes in electrophysiological measures of amplitude are in agreement with changes in perceived contrast.
Visual acuity in young and old adults under low luminance
Authors: Sturr Joseph F. , Kline Gary E. , Taub Harvey A.
Published: February 2023

Static visual acuity has traditionally been used for characterizing visual performance in the well-illuminated environment. However, there is very little information available on the performance of the aging visual system under mesopic and mesopic/scotopic conditions. The present study has been designed to help clarify and extend previous findings in this area. Young (ages 18-25, N = 40) and old (ages 60 and above, N = 80) subjects in good ocular health were tested binocularly for distance acuity with a Bausch & Lomb Orthorater at each of six luminance levels ranging from 245 to 0.2 cd/m2. All began at the lowest level and continued at each progressively higher luminance. Preliminary results suggest (1) age-related losses in acuity at all luminance levels, (2) a systematic decline in performance over each 5-yr interval beginning at age 60, (3) 80% of those over 65 were legally blind at the lowest illumination condition, and (4) performance at the highest level is a relatively poor predictor of visual acuity at the lowest level of illumination for all subjects.
MTF measurements on the human crystalline lens
Authors: Block Michael G. , Rosenblum William M.
Published: February 2023

The purpose of this paper is to describe the methods and results of modulation transfer function (MTF) measurements on the human crystalline lens. To better understand the optical qualities of the crystalline lens we applied similar MTF measuring techniques on both human and animal lenses. Freshly excised crystalline lenses were suspended in a balanced salt solution cell, and the lenses were held in position only by their intact zonulae and ciliary body. An annulus of sclera was the only contact between the holder and the tissue. The holder was placed in an optical bench MTF measuring apparatus. A 5-μm slit was used as an object in a collimated system, and the aerial image produced by the crystalline lens was examined by a scanning microscope photometer. The spread function was Fourier transformed to obtain the MTF of human crystalline lenses (age 1 month and 55 yr) and animal (six cow and seven dog) lenses.
Evaluation of functional vision of 257 cataract patients using the Vistech sensitivity chart
Authors: Ginsburg Arthur P. , Richburg Frederick A. , Tedesco John
Published: February 2023

Visual acuity is still the main measure used to quantify visual loss from cataracts by medical, legal, and government institutions. However, much research shows that acuity alone is not a proper measure of vision loss due to cataracts. Contrast sensitivity measurements have proved increasingly important for determining functional vision loss. Although previous contrast sensitivity research used computer-controlled video systems, more recently, a new contrast sensitivity test, the Vision Contrast Test System (VCTS), has been developed to measure functional visual capability for routine clinical testing of contrast sensitivity. Initial results of the VCTS for a wide variety of visual pathologies revealed contrast sensitivity losses simitar to those found using computer-controlled video systems.
Test-retest reliability of three methods for measuring contrast sensitivity
Authors: Rubin Gary S. , Morrison Constance
Published: February 2023

Clinical applications of the contrast sensitivity function (CSF) have dramatically increased over the past decade. The CSF has been recommended for use in diagnosing vision disorders as diverse as glaucoma, age-related maculopathy, and retinitis pigmentosa. The CSF has also been proposed as a test for visual screening, as a technique for assessing visual function in patients with low vision, and even as a means of increasing revenue in clinical practice. Traditional methods for measuring contrast sensitivity require relatively expensive and sophisticated equipment and employ time-consuming psychophysical procedures. Recently, several contrast sensitivity tests have been developed, primarily for clinical use, which are inexpensive, quick, and simple to administer. The value of these new tests depends on the accuracy and reliability with which they measure contrast sensitivity.
Collisional mixing of the two upper levels of copper-vapor lasers
Authors: Kim Jin J. , Sung Nackchin
Published: February 2023

We report the first direct evidence that there is collisional mixing between the 2P3/2 and 2P1/2 levels of the copper-vapor laser (CVL), which is excited by a resonant tunable UV laser. When the 2P1/2 level is pumped which generates a yellow laser line (578.2 nm) by a transition to the 2D3/2 level, the 2P3/2 level is also populated, producing a strong green laser line (510.6 nm). On the other hand, when the 2P3/2 level is excited which produces a green laser line by a transition to the 2D5/2 level, the 2P1/2—2D3/2 transition is only weakly stimulated. The collisional mixing takes place in a wide range of He buffer gas pressure: 20-600 Torr. Below 20 Torr, only the primarily pumped level is strongly stimulated. The asymmetric mixing has significant implications for high-pressure transverse discharge CVLs.1 Also, we observed that each transition is stimulated even when the pump laser is detuned as far as 1 nm from the resonance wavelength, indicating that they are collision-induced stimulated emission.
Pulsed room-temperature operation of a tunable NaCl color center laser
Authors: Culpepper Charles F. , Carrig Timothy J. , Pollock Clifford R.
Published: February 2023

A tunable pulsed color center laser using additively colored OH−-doped NaCl is discussed. The laser has produced output energies exceeding 8 mJ in 20-ns pulses. This energy is four times greater than that reported for previous pulsed color center lasers. More significantly, this performance has been achieved with a room-temperature crystal. The laser has a tuning range which extends from 1.37 to 1.77 µm. Based on the observed spectral properties of the center1 and the laser tuning curve, laser action at room temperature is tentatively ascribed to

F
2
+

centers. The OH ions are necessary for producing a sufficient

F
2
+

population. A positive branch unstable resonator was used, which, because of a 50% reflective output coupler, produced a filled-in mode. The laser was operated for up to 40 h during which time the output power faded 40%. Crystal preparation, cavity and pump scheme, fading mechanisms, and laser results are explained. In addition, cryogenic and room-temperature operation are compared.
Intensity correlations in a laser with multiplicative noise
Authors: Young M. R. , Phillips K. J. , Singh Surendra
Published: February 2023

The time-dependent solutions of the Fokker-Planck equation for a single-mode laser with white noise loss fluctuations are studied theoretically. Both the multiplicative and additive noise sources are included in the treatment, and they have comparable strengths. Experiments were carried out on a single-mode He-Ne laser. Multiplicative noise was introduced by applying a noise voltage on an intracavity loss element. The steady-state correlation functions of the laser were determined from the photoelectric correlation measurements, and their behavior with multiplicative noise strength was studied in the pump parameter range a = –10 to a = 10. The results of these measurements are compared to the theoretical predictions.
Incoherent pump effects in AM spectroscopy
Authors: Chakmakjian Stephen H. , Koch Karl , Stroud C. R. , Hillman Lloyd W.
Published: February 2023

The response of three- and four-level homogeneous laser systems to an amplitude modulated field in the presence of an incoherent pump is treated using a rate equation model. A spectral hole due to the finite bandwidth of the population oscillations is observed with a modulated field at either the pump or the laser frequency. The spectral width of the hole broadens at a rate proportional to the sum of the dimensionless intensities of the pump and laser fields. The power levels required to broaden the 1/T1 hole in various laser systems is presented. The experimental implications of this result are discussed.
Multimode pumping of a tunable far-infrared Raman laser
Authors: Rai Jagdish , Izatt J. R.
Published: February 2023

Stimulated Raman scattering provides a powerful and relatively efficient source of tunable coherent far-infrared (FIR) radiation.1,2 The pump field is usually an intense multimode CO2 laser. Most theoretical studies of FIR lasers consider the pump to be a single-mode field. We present some analytic results for the gain of optically pumped FIR lasers when the pump field has a large number of cavity modes with spacing Δ. The molecular medium can have three or four levels.
Spectroscopy of the 3-µm laser transitions in YAlO3:Er
Authors: Stalder M. , Luthy W. , Weber H. P.
Published: February 2023

Temporal sequences of different spectral components of the 4/11/2 → 4/13/2 manifold in YAlO3:Er have been analyzed in a laser operated at 300 K. Several lines can oscillate in a spiking train. Their position in the pulse is discussed in terms of population inversion, laser linewidth, and resonant ion-ion interaction. Erbium crystals with dopant concentrations of 10, 20, and 50% have been used in the experiments. The wavelengths of the 3-µm transitions range from 2.71 to 2.92 µm. They are strongly dependent on the crystal orientation with respect to the polarization of the laser light. The polarization dependence of the most prominent emission lines has been determined for laser crystals oriented with their axes along the crystallographic a and b directions. The bandwidth of the laser lines has been measured with a resolution of 0.12 nm using a grating spectrometer in combination with an image converter. The bandwidth ranges from 0.3 nm at 2.73µm up to 2.6 nm at 2.92 µm.
Squeezed states of light
Authors: Teich Malvin C.
Published: February 2023

No summary of this tutorial or biographical information was available at press time.
Precision measurement beyond the shot-noise limit
Authors: Xiao Min , Wu Ling-An , Kimble H. J.
Published: February 2023

Improvements in precision beyond the limit set by the vacuum state or zero-point fluctuations of the field are reported for two optical experiments. Both experiments employ the squeezed light from an optical parametric oscillator to reduce the level of fluctuations in one of two quadrature phase amplitudes below the shot-noise level (SNL). The first experiment follows the work of Caves1 on precision interferometry with squeezed states. An increase in signal-to-noise of 2.5 dB relative to the SNL is demonstrated for the detection of phase modulation in a Mach-Zehnder interferometer. In the second experiment amplitude modulation is encoded on a weak signal beam with an acoustooptic modulator. For the case of a squeezed signal beam compared with a beam in a coherent state, an improvement in sensitivity of 2.5 dB is achieved for the detection of amplitude changes of the field. The observed increases in sensitivity in both experiments are currently limited by simple linear losses in propagation and detection and not by the degree of available squeezing.
Squeezing more out of a laser
Authors: Caves Carlton M.
Published: February 2023

Machida and Yamamoto used negative feedback from a conventional photodetector to stabilize a laser's intensity and thus to obtain sub-shot-noise photon statistics within the feedback loop. Out-of-Ioop light extracted at a beam splitter, however, displayed super-shot-noise statistics. This behavior can be understood both quantum mechanically and semiclassically. Quantum mechanically the culprit is the vacuum field that enters the beam splitter’s second input port. I describe a technique for extracting sub-shot-noise light by replacing the culprit vacuum field with squeezed light generated by a nonlinear device—a squeezer—that is pumped by a portion of the laser light. Moreover, even if the unstabilized laser is shot-noise-limited, the extracted light can have a better intensity SNR; this signal-to-noise improvement requires both feedback and squeezing.
Homogeneous squeezing, spectral component squeezing, and the degree of squeezing
Authors: Hong C. K. , Ou Z. Y. , Mandel Leonard
Published: February 2023

The definitions of homogeneous squeezing, inhomogeneous squeezing, spectral component squeezing, and degree of squeezing are introduced for an optical field that is not necessarily squeezed in the full sense. They are then applied to three different examples of squeezed states. It is shown that in resonance fluorescence from a two-level atom the squeezing is homogeneous when the relative Rabi frequency Ω/β < 1, inhomogeneous when

1
<
Ω
/
β
<

2

, and spectral component-type squeezing when

Ω
/
β
>

2

, and the maximum degree of squeezing is 28%. For the process of downconversion in a resonant cavity the squeezing is homogeneous with a 100% maximum degree of squeezing. In the process of four-wave mixing the squeezing is always inhomogeneous, and there is a domain of spectral component squeezing, but the degree of squeezing can be 100% in certain circumstances.
Spatial structure in optical phase conjugate resonators
Authors: Klemas Andrew , Kramer Mark A. , Martinez David R. , Rubin Lawrence F.
Published: February 2023

It has been noted by others that the spatial beam quality and stability of phase conjugate resonators have been improved by introduction of intracavity apertures. Such apertures are effective at reducing the number of allowed modes for the phase conjugate resonator. Allowing a large number of modes to run adversely affects clean propagation of the beam. Our paper examines the mode structure of the field in a phase conjugate resonator. The phase conjugate resonator was composed of a self-pumped barium titanate crystal and a conventional mirror setup in a self-oscillating configuration. The intracavity mode structure was sampled using a shear plate. We find that the mode structure is dramatically improved by insertion of appropriately sized intracavity apertures. Aberrations placed between the conventional mirror and the intracavity aperture were found to destroy the phase conjugate nature of the counterpropagating fields in that region of the cavity.
Real-time one-way complex optical field imaging through a distorting medium by conventional phase conjugation
Authors: Li Zaichun , Zhang Yimo
Published: February 2023

Imaging through distorting media via phase conjugation techniques requires a double-pass transmission of the image field through the same distortion. 1 Using a phase conjugate window (PCW), complex optical fields can be transmitted through thin distorting media in a single pass.2 Since the image-bearing wave is used as one of two pump waves, there always exists an effective phase mismatch between the pump waves. This, however, imposes a limit on this approach. We present and analyze theoretically an alternative method for one-way complex optical field imaging through thin distorting media by conventional phase conjugation and four-wave mixing, in which two planar waves are employed as the pumps. As a result, no phase mismatch exists. Either an original object field (a 3-D field in theory) or the complex conjugate of an original field can be obtained. Also presented is a possible system for experimental implementation. Two identical optical channels are used in the system, one for input object field, another for output conjugate field. It is noted that the distortion here, together with the input image, need not be imaged onto the nonlinear mixing medium, as opposed to the PCW scheme.2
Measurements of the mode structure of a phase conjugate resonator
Authors: Skeldon Mark D. , Boyd Robert W.
Published: February 2023

The mode structure of an oscillator consisting of a phase conjugate mirror (PCM) and a conventional mirror (CM) has been discussed by several authors.1 These oscillators exhibit different behaviour than their conventional counterparts. In particular, a phase conjugate oscillator (PCO) is always geometrically stable regardless of the cavity length or the CM radius of curvature, positive or negative. We have constructed a PCO which incorporates a PCM based on a Brillouin-enhanced four-wave mixing process that has been discussed previously.2 This PCM has a reflectivity greater than unity and no frequency shift on reflection; hence this PCM facilitates PCO designs which lend themselves to simple theoretical analysis.
Theoretical model of disparity gradients
Authors: Yuille A. , Bulthoff H. , Fahle M.
Published: February 2023

Recent studies on the perception of disparity gradients show that the perceived difference in depth between two stimuli decreases continuously with increasing steepness of the disparity gradient, i.e., decreasing interocular distance between stimuli.1 This scaling effect is stronger for horizontal than for oblique orientations and also stronger for line stimuli than for point stimuli. We propose a model to explain the scaling effect based on minimizing an energy function. Since the visual system is not able to determine the retinal positions of the stimuli exactly, our model allows for uncertainty in these positions. Our energy cost function tries to find the smoothest possible surface allowing for this uncertainty. For the stimuli described above we analyzed the model mathematically and performed computer simulations when necessary.
Quantum statistics of stimulated Raman scattering using a Gaussian-profile pump
Authors: Kuo S. J. , Radzewicz C. , Raymer M. G.
Published: February 2023

An experimental study of stimulated Raman scattering (SRS) has been performed using a subnanosecond pulse to investigate the statistical properties of Stokes light generation.1 There are macroscopic fluctuations of Stokes pulse energy as well as random generation of spatial mode patterns. When the scattering volume has a low Fresnel number, the spatial patterns of the SRS resemble cavity modes. When the Fresnel number is large, there are irregular structures appearing across the Stokes profile in a random fashion. A theoretical study of the spatial and temporal coherence properties of Raman generation using a Gaussian-profile pump pulse has also been carried out. Using a Gaussian-Laguerre mode expansion technique,2 it is found that the higher-order spatial coherence modes1 experience different gain than the lower-order spatial coherence modes, and consequently the temporal coherence associated with each individual spatial coherence mode is different.
Linear theory of Raman beam cleanup and amplification in a crossing beam geometry
Authors: Menyuk Curtis R.
Published: February 2023

In experiments which have been performed to date at the Naval Research Laboratory,1 it has been discovered that the results can be characterized by the Fresnel number of the aberrations

D
A
2

/
λ
L

, where D
A
is the transverse scale length of the aberrations, L is the interaction length of the pump and Stokes beams, and λ is the pump wavelength. The results are characterized by the geometry (collinear or crossing beam) and aberrations (phase, amplitude, or both). We show that many of the experimentally observed effects can be explained by a linear theory, although nonlinear effects due to pump depletion are in most cases important. The circumstances in which off-angle contributions, copropagating with the crossing beams, are seeded by the pump and can grow to important levels are elucidated.
Conical emission in a small high-density sodium environment
Authors: Pender John , Hesselink Lambertus
Published: February 2023

Two types of conical emission in sodium have appeared in the past. In the first, a single tightly focused laser beam is tuned to the blue side of the D1 line in conditions compatible with self-trapping. The emission is specular, has a cone half-angle of a degree, and occurs on the red side of line center. In the second type, two weakly focused counterpropagating laser beams are tuned to the red side of line center. The emission consists of radial filaments, has a cone half-angle of 8°, and is the same wavelength as the pumps. We report on yet a third type of conical emission which is distinct from the first two types by virtue of its spatial and spectral characteristics. Like the first type, the pumps are tuned to the blue side of line center, the emission has a cone half-angle of a degree and is specular. However, this phenomenon also resembles the second type of conical emission in that two counterpropagating pumps are required, the pumps are weakly focused, and the emission wavelength is the same as the pumps.
Nonlinear refractive-index measurements of air and argon gases at 1 atm
Authors: Pennington D. M. , Henesian M. A. , Swift C. D. , Hellwarth R. W.
Published: February 2023

Experiments were performed using the Lawrence Livermore National Laboratory Nova laser to measure the nonlinear refractive index of air and argon gases via the technique of intensity-dependent ellipse rotation. These measurements directly impact our understanding of beam propagation issues and solid-state frequency conversion performance for large laser systems. Our experimental values for the nonlinear refractive index at 293 K, 1 atm, are ~0.98 × 10−16 esu for air and 0.23 × 10−16 esu for argon. We surveyed the recent literature to compile what we consider the most reliable values for the nonlinear indices of air (nitrogen and oxygen) and argon. This has been accomplished by deducing the third-order susceptibility tensor components for the optical Kerr effect from precise measurements of the dc Kerr effect and electric field-induced second harmonic generation reported in the literature.1 Our ellipse rotation measurements and calculations confirm that the nonlinear indices for air are substantially lower than previously reported.2 Thus nonlinear refraction over long air paths has less impact on diffraction and frequency conversion in large laser systems than previously believed.
Stimulated Raman scattering with pulse trains of alternating sign
Authors: Reintjes J. , Duncan M. D. , Calame G. , Tankersley L. L. , Mahon R.
Published: February 2023

We describe stimulated Raman amplification of a train of pulses of alternating sign in conditions in which multiple pulse effects are important. We previously demonstrated experimentally and theoretically that for a train of nonalternating pulses the Raman gain can grow to be several orders of magnitude greater than that of a single pulse. When the sign of the pulses in either the pump or the incident Stokes train (but not both) alternates, the amplified Stokes pulse train, after an initial transient involving high gain, evolves to a dynamic steady state with an amplitude that can be many orders of magnitude below the corresponding level achieved with a nonalternating train. At its dynamic equilibrium the Stokes amplitude within a pulse oscillates or changes sign depending on the specific conditions. The dependence of the equilibrium Stokes intensity on parameters such as pulse separation and single pulse gain is described. The relationship of the behavior observed here to stationary solutions of the transient Raman equations is explored, and comparisons to effects due to phase oscillations in longer pulses is made.
Aspherical surface characteristics of TV projection lenses
Authors: Betensky Ellis
Published: February 2023

Although aspherical surfaces have been employed to provide aberration correction in special applications, there has been no general acceptance of their general utility, perhaps because lens designers have always wished for the opportunity to remove the residual aberration by aspherizing a surface, and as a result most existing designs having aspherical surfaces are thus characterized. A methodology for designing systems in which primary aberrations, other than chromatic and Petzval curvature, are corrected by aspherical surfaces has been suggested by Kross et al.1
Aberrations of the fifth order and the concept of eikonals
Authors: De Meijere J. L. F. , Velzel C. H. F.
Published: February 2023

A derivation of the fifth-order aberrations for a system of centered spherical surfaces is presented. The fifth-order aberrations are partitioned into surface contributions. The method contains two novel features. First, the theory is based rigorously on the concept of the angle characteristic function (eikonal) for a single surface only. Starting from the single-surface eikonal, expressions for third-and fifth-order aberrations, as well as third-order pupil aberrations, are formulated. Second, the problem of finding the aberration coefficients for a system of surfaces is reshaped into the problem of solving a set of coupled nonlinear equations. Application of Lagrange's theorem up to fifth order then yields the expressions for the third-and fifth-order aberration coefficients at once. In this way, Buchdahl’s iteration procedure can be avoided.
Shortcomings in applied optics education
Authors: Goodman Douglas S.
Published: February 2023

Applied optics comprises a body of knowledge on which modern technology rests. Nevertheless, there is an alarming shortage of new Ph.D.s trained in the area of applied optics/optical engineering/ optical instrumentation. Several factors contribute to this situation. Applied optics has a vast history and requires a range of skills necessary for its practice, but it is not recognized—as it should be—as a major field of study. The challenge and pleasure of building precise instruments is insufficiently recognized, much less extolled as the challenging pursuit that it is.
Low-loss GaAs/AlGaAs optical waveguides and bends
Authors: Deri R.J. , Kapon E. , Schiavone L.M.
Published: February 2023

Low-loss semiconductor waveguides and bends are essential for integrating optical guided-wave devices with electronic circuitry. We have fabricated rib waveguides on GaAs/AlGaAs single heterostructures with losses as low as 0.25 dB/cm and much greater optical confinement (effective index difference Δn = 0.012) than in previously reported semiconductor guides of comparable loss (Δn ≤ 0.003).1,2 Scattering from rib roughness is a significant loss contribution in ion-milled rib waveguides; the loss is described by a rib roughness of 50 nm using a simple formula3 for the scattering loss. Smoother rib walls can be obtained by other etching methods, however. The effect of rib geometry and fabrication method on the scattering loss is discussed. Bends with low radiation loss (≤0.6 dB/rad) and small radius (several millimeters) were fabricated with such guides.
Pulse distortions at the coupling between parallel dielectric waveguides
Authors: Hong B.J. , Yang C.C.
Published: February 2023

The advance of integrated-optics technology has increased interest in guided-wave phenomena. The problem of coupling between parallel dielectric waveguides has been extensively studied. However, the previous discussions are made only for the coupling of a single-frequency wave. In this research, we investigate the problem of conversion of a pulse from one waveguide to the other. The pulse is first decomposed into different frequency components. The coupling between waveguides for each component can be evaluated by using the well-developed coupling theories. The coupled pulse is simply a superimposition of many coupled components. Because the coupling coefficients for various frequency components are different, the coupled pulse is distorted. These distortions are examined for both TE and TM modes. A two-waveguide system is discussed first. Then, a system with more than two parallel waveguides is studied. Also, in evaluating the coupling strength, the conventional coupling formalism is used. However, the modified theory by Streifer is considered as well.
Modeling of Ti:LiNBO3 directional couplers by a 2-D beam propagation method
Authors: Koai Kwang T. , Liu Pao-Lo
Published: February 2023

A beam propagation method (BPM) provides a useful approach to the simulation of most guided-wave devices because (1) it treats the guided and the radiating fields with the same formalism; (2) it can analyze device structures which vary along the propagation direction.1 Instead of the 3-D BPM approach, which usually needs a supercomputer, we used a 2-D BPM approach to model Ti-diffused directional couplers on LiNbO3 fabricated by Alferness et al.,2 Noda et al.,3 and Feit et al.4 The 1-D effective-index profile was calculated to replace the transverse 2-D refractive-index profile. The input variables were optical wavelength, diffusion temperature, diffusion time, and the thickness, width, and locations of the titanium strips. The anisotropic diffusion constants and the relation between refractive-index change and titanium concentration found in Ref. 5 were used in computation. However, since different fabrication conditions and wavelengths were used by different groups, slight adjustments of the diffusion lengths and the index change vs Ti concentration were necessary to fit all data.
Accuracy of geometric moments computed from Hartley intensity
Authors: Kumar B.V.K. Vijaya , Fitzpatrick Craig
Published: February 2023

Recently, Bracewell introduced a new transform called the Hartley transform (HT). This transform has the distinct advantage that HT of a real signal is also real. Thus, use of HT can potentially overcome some of the problems associated with Fourier transform (FT)-based methods which require the detection of complex wavefronts. Recently, Vijaya Kumar1 proposed a new algorithm to compute image moments (useful for pattern recognition) from the Hartley transform intensity. We investigate the accuracy of moments computed using this algorithm when the algorithm is subjected to realistic impairments. The impairments considered include image plane noise, HT plane noise, sampling interval in the HT plane, dynamic range of the HT plane detectors, alignment requirements, and limited number of HT plane detectors.