bluuebunny/crossref_metadata_2025 huggingface dataset:
Broadband Tunability of Gain-Flattened Quantum Well Semiconductor Lasers with an External Grating
Authors: Mittelstein Michael , Mehuys David , Yariv Amnon , Sarfaty Rona , Ungar Jeffery E.
Published: February 2023

The spectral tunability of quantum well semiconductor lasers is found to approach the range of dye lasers. Gain spectra calculations predict, for a particular pumping condition, a wide spectral range of nearly flat gain from quantum well lasers. This flattening results from contributions to the gain, at high pumping current, from electron-hole transitions in the second (n = 2) quantized state. In addition, the gain spectrum is stretched out to shorter wavelengths. Consequently, properly designed quantum well lasers can have an effective tuning range 2 to 3 times that of conventional semiconductor lasers. This flat gain spectrum enabled us to tune broad area, single quantum well lasers over a spectral width of 90 nm with an external grating. No antireflection coating of the lasers was required. Rather, the condition of broad, flattened gain was achieved by optimizing the length of the lasers to near 200 μm. Power output from the free side of the tuned lasers exceeded 200 mW (pulsed) in a single longitudinal mode over most of the spectrum. The 11% tuning range achieved is the largest published value for a semiconductor laser. This work was supported in part by the National Science Foundation and the Office of Naval Research, and M. Mittelstein acknowledges support from a Newport Research Award.
Slowing and Cooling an Atomic Beam Using an Optical Standing Wave
Authors: Prentis M. , Cable A.
Published: February 2023

We have demonstrated that a continuous supply of slow atoms can be produced using a strong standing wave laser field collinear with an atomic beam.
Multiband infrared focal plane array sensor system
Authors: Gallagher L. , Bender R. , Edrich D. , Zimet S. , Crowder D.
Published: February 2023

The focal plane array (FPA) infrared search and track (IRST) system is a scanning multiwavelength IR sensor. The system is used for measurement of the spatial distribution of sky radiance in three spectral bands within the 3-5 μm infrared region. It also has the capability to analyze digitized data samples (using digital filters, logic circuits, and multicomputer signal analysis processing equipment) to identify pointlike radiation sources which exhibit spectral signatures characteristic of hydrocarbon-burning aircraft.
Image degradation and preservation in photorefractive amplifiers
Authors: Vachss Frederick , Yeh Pochi
Published: February 2023

Image amplification through photorefractive two-beam coupling has been demonstrated by several investigators in the last decade.1 In these demonstrations, high image fidelity was retained in the amplified image in the limit where the intensity of this image remained small compared with that of the pump beam from which it received energy. When this condition is violated, however, and the image and pump intensities become comparable, the gain of the amplification process becomes a nonlinear function of the image intensity, resulting in distortion and contrast reduction of the amplified output image.2 This situation is encountered, however, in all power-limited applications where large fractions of incident pump energy must be transferred to the image. We thus examine this regime of image amplification with strong pump depletion and consider techniques through which the associated nonlinear image degradation may be reduced. Specifically, by analyzing the two-beam coupling process in the presence of complex wavefronts, we may determine both the form of the image wave and the experimental geometry for which the amplified fidelity is maximized. These analytic results are then compared to experimental studies of image amplification in photorefractive SBN over a broad range of experimental conditions.
Dynamics of refractive-index grating formation in a Kerr medium
Authors: Saxena Ragini , Yeh Pochi
Published: February 2023

Light-induced change in the index of refraction of a Kerr medium is well known.1 Illumination with a spatially periodic light intensity leads to the formation of an index grating in the Kerr medium. We make a comparative study of the response time and power requirement for index grating formation in photorefractive and Kerr media. We examine the conditions in which the index grating in the Kerr medium will be spatially shifted from the light intensity that induces it. Two-beam coupling via Bragg diffraction from the nonlocal index grating is studied.2 The coupling constant is found to depend on the relaxation mechanism of the atoms in the Kerr media and the frequency detunings of the two beams from the line center.
Attenuation coefficient and scattering phase function of human tissues
Authors: Marchesini R. , Andreola A. , Bertoni A. , Melloni E. , Sichirollo A. E.
Published: February 2023

The wide development of lasers in medicine and surgery has increased the interest of studying propagation of light in mammalian tissues. Since few and contrasting data about optical parameters of human tissue have been reported, our aim was to add further information by directly measuring extinction and absorption coefficients and a single scattering diagram. Thin sections, from 0.05 to 0.2 mm thick, of various human tissues were cut with a microtome from frozen samples. The slices, after having been hydrated with saline, were placed between two optical grade glasses and sealed. The extinction coefficient was evaluated by measuring the light, delivered through an optical fiber from an argon-dye laser, transmitted on-axis and within 2 × 10−5 sr. The absorption coefficient was measured by placing a specimen into an integrating sphere. The scattering coefficient was evaluated by the difference between extinction and absorption. The scattering diagram was evaluated by positioning a specimen in a cylindric tank filled with saline. Light scattered within 25 mrad was measured at different angles. The following table shows the values of scattering s and absorption a coefficients and the average cosine of scattering g for various tissues at 635-nm wavelength.
Effects of configuration on the perceived rigidity of rotating polyhedra
Authors: Sparrow John E. , Stine W. Wren
Published: February 2023

Parallel projections of rigidly rotating stimuli were studied in a kinetic depth paradigm. Five subjects viewed four types of eight-vertex object: (1) line drawings of polyhedra with randomly placed vertices: (2) line drawings of polygons with randomly placed vertices where the initial orientation was constrained to appear as a Necker cube; (3) vertex-only drawings with randomly placed vertices; and (4) vertex-only drawings with randomly placed vertices and the Necker cube constraint. Some rigidly rotating objects take on a nonrigid quality (e.g., Green,1 Sparrow and Stine2). A five-point rating scale (1 = rigid, 5 = nonrigid) was used to indicate the perceived rigidity in all four conditions. Most of the stimuli received ratings of 1. However, the line drawings with the Necker cube constraint elicited the highest number of deformation ratings. Stimuli from the remaining three conditions received rating distributions that were not discriminable from one another. This study was replicated using a larger group of observers (N = 28). A second group (N = 27) judged the perceived direction of rotation to test Green’s2 reversibility hypothesis. Finally, the observer’s ability to discriminate rigidly rotating stimuli from nonrigidly rotating stimuli was measured using TSD.
Effects of stereo illusion induced by binocularly presented gratings
Authors: Chao Gung-Mei , Odom J. Vernon
Published: February 2023

Vertical square-wave gratings were binocularly presented to subjects on a video monitor. The stereo illusion of several discontinuous levels of depth was seen as previously reported.1 We examined the parameters of this illusion. (1) The number of levels seen varied as a function of spatial frequency at a constant viewing distance of 63 cm and a constant visual field size of 18.5 × 23.3°. Spatial frequencies were varied from 0.8 to 8.8 cycles/deg in 1-cycle/deg steps. (2) If the vertical gratings were reversed there was no significant change in the number of levels seen within the examined range from 0 to 15 Hz at a spatial frequency of 4 cycles/deg. (3) The contrast of 3-cycle/deg gratings affected the probability of seeing the stereo illusion. When the contrast is 10%, ~50% of the time two or more levels of depth were seen. When contrast reached 30%, 100% of the time two or more levels of depth were seen. The monitors had mean luminance of 106 cd/m2for above-mentioned studies (1) and (2) and 164 cd/m2 for study (3).
Measurement of calcium in a single cell with a digitizing imaging fluorescence microscope
Authors: Yelamarty Rao V. , Cheung Joseph Y. , Yu Francis T. S.
Published: February 2023

Optical section microscopy furnishes advantages over physical sectioning in visualizing the 3-D structure within a living cell. A hybrid digital-coupled fluorescence microscope for optical sectioning the specimen has been developed to measure the 3-D distribution of calcium in a single cardiac cell. The cell is initially loaded with fura-2, a fluorescent calcium-sensitive Indicator, and a stack of sectional fluorescent emission Images corresponding to different focal settings along the microscope’s axis of the specimen are obtained and then digitized for postprocessing. The experimental defocused point spread and contrast transfer functions of the overall system have been measured using the Ealing resolution target. Each sectional image of the stack is then processed digitally, using spread functions, by a VAX 11/780 to eliminate the defocused light contribution using the method described by Agard.1 The stack of 2-D processed images is then displayed on a multiple pixel system to observe the 3-D distribution. We show results of 3-D calcium distribution in a cardiac muscle cell and its dynamic variation during metabolism achieved by our system.
Phase locking and the correlated emission laser
Authors: Winter M. P. , Hall John L.
Published: February 2023

Recently, there have been reports of observations1 of correlated spontaneous emission2 in laser systems (CELs). There may still be some confusion, however, in the interpretation of these results. In particular, the distinction between CEL operation and ordinary phase locking (PLL) has not been clarified. Experimentally, we exploit the phase sensitivity and time dependance of the phase diffusion to differentiate between the PLL and CEL cases in a Zeeman laser. The phase-locking equation can be approximated in a parametrized form:
Comparison of inner and outer product neural associative retrieval via computer simulation
Authors: Liu Hua-Kuang , Chao Tien-Hsin , Barhen Jacob , Bittner Graf
Published: February 2023

The inner-product approach1,2 is an alternative way of performing optical implementation of neural associative retrieval. With the inner-product approach, the interconnection matrix is realized by directly storing the binary memory vectors in two spatial planes in tandem. Thus there is no saturation problem with the spatial light modulators realizing the interconnection matrix, and the precalculation of the outer-product interconnection matrix is not needed. Moreover, the optical storage space is about an order of magnitude smaller compared with that of the outer-product approach.
Diode laser spectroscopy of pressure broadening of 12CO2 and 13CO2 lines
Authors: Becker Joseph F. , Yaldaei Ramil , McKay Christopher P.
Published: February 2023

Lead-salt tunable diode lasers (TDLs) emit with a very narrow linewidth of ~0.0003 cm−1. This spectral resolution is much narrower than typical Doppler broadened linewidths in the mid-IR range. It is thus possible to detect individual rotational lines within the vibrational band and measure their intensity, which can be used to determine gas concentration and isotopic ratio. The 2300-cm−1 spectral region is especially interesting because the 12CO2 and 13CO2 bands overlap so that their rotational lines have approximately equal absorbance at the anticipated isotopic ratio (~90) of atmospheric CO2 on earth and Mars. To characterize pairs of spectral lines used for isotopic ratio measurements in our stable isotope laser spectrometer, we measured the effect of pressure variations on the spectral line shape of 12CO2 and 13CO2 rotational lines in the 4.3-μm band. Two lines we have studied are (most likely) the R(20) lines of 13CO2 (2298.503 cm−1) and the P(54) line of 12CO2 (2298.278 cm−1). These two lines are separated by only 0.225 cm−1 but are well resolved using a TDL. They have approximately equal absorbance at the normal isotopic concentrations of CO2 on earth and Mars. These lines begin to broaden with increasing pressure at ~2 Torr. The measured profiles compare favorably with theoretical calculations.
Fluctuation properties of a dye ring laser with controllable asymmetry
Authors: Gage E. C. , Mandel Leonard
Published: February 2023

By inserting a specially constructed optical diode, whose losses differ by a controllable amount for waves traveling in opposite directions, into the cavity of a two-mode dye ring laser, we succeeded in studying the statistical fluctuation properties of the laser as a function of asymmetry. This includes the moments of the light intensities, their probability distributions, and the on and off probabilities for each mode. We also observe hysteresis in the mean light intensity when the asymmetry is varied cyclically. The experimental results are compared with analytic solutions of the equations of motion without pumping fluctuations and with computer solutions with pumping fluctuations. Reasonable agreement is found in almost all conditions in the latter case. But even the analytic solution gives a fair account of the experimental results, provided the difference pump parameter in certain expressions is scaled up by a factor of 20.
Acoustooptic nonlinear device
Authors: Poon Ting-Chung , Cheung Sui Kwan
Published: February 2023

Acoustooptic hybrid bistable devices have been studied previously. However, no actual comparison and correlation have been made between experimental results and theoretical predictions. We first present a model for the nonlinear device. The model includes the theory of acoustooptic diffraction in the near-Bragg regime in which the Klein-Cook Bragg parameter Q is finite.1 Computer simulations will then be shown in which it suggests that the performance of the bistable device using a low Q acoustooptic device can be improved by adjusting the feedback gain. Finally, we present experimental results which confirm the validity of the theoretical model.
Acoustooptic deflectors at cryogenic temperatures
Authors: Fuss Ian , Smart Darryn
Published: February 2023

Acoustooptic deflectors that operate over the 3-300-K temperature range have been constructed. The acoustic attenuation of the L[001] mode of TeO2 and the L[100] mode of GaP has been measured, using these devices, at frequencies between 0.7 and 1.3 GHz and at temperatures spanning 3-300 K. These measurements show a significant decrease in the acoustic attenuation of ~X6 when the device temperature is decreased from room temperature to ~ 10 K. More than that the measurements show that the frequency dependence of the acoustic attenuation changes from nominally quadratic at room temperatures to almost none at 10 K.
Multilayer alignment mark-induced offsets in microlithography
Authors: Gallatin Gregg , Duryea T. , Webster J. C.
Published: February 2023

The scattering matrix approach to computing the image of a multilayered structure1 is used to study alignment mark-induced offsets in microlithography. The sensitivity of the offset to different types of illumination and imaging system, to misalignments in the illumination and imaging optics, and to different alignment mark structures is presented. In particular, reverse dark-field imaging is studied in detail. The effects of nontelecentricity and coma for several alignment mark shapes are presented. The offsets are shown to be particularly sensitive to alignment mark shape and to layer thickness as well as aberrations. To obtain offsets that are less than a tenth of a micron with a given range of aberration and misalignment in the optics requires the use of particular alignment mark shapes or the use of a more sophisticated algorithm for determining the mark position from the image. The basis of the scattering matrix approach to imaging layered media is briefly discussed for the purposes of understanding the results of the model.
What's so ultra about ultrasqueezed light?
Authors: Schumaker Bonny L.
Published: February 2023

At a previous OSA conference the author introduced the phenomenon of ultrasqueezed light, produced by three-wave and four-wave mixing in nonlinear media pumped at multiple frequencies spaced so as to produce appropriate phase-matching. Here quantitative results are given of the advantages offered by ultrasqueezing in terms of the degree of squeezing obtainable for a given total amount of input pump power. Phase-matching requirements and detection techniques are described, and resulting implications for the usefulness (enhanced squeezing vs ease of production and detection) are indicated. The results differ appreciably for three-wave and four-wave mixing. Several different experimental schemes for producing ultrasqueezed light are described using three-wave and four-wave mixing. Only one of these, four-wave mixing with two pump frequencies in an optical fiber, has been attempted experimentally; its success has been described at a previous OSA conference and is reviewed only briefly. Comparison is made between ultrasqueezed light and pulsed squeezed light, which can be viewed as a special limit of ultrasqueezing with many pump frequencies.
Digital image processing based on the M-ary extension of the hopfield neural network model
Authors: Bijjani R. , Das P.
Published: February 2023

The associative content-addressable memory proposed by Hopfield has a good tolerance for errors and is capable of solving image recognition problems. The error correction capability for such a model of size N is limited to (N − 1)/2 bits, which is just under 50%. Our proposed M-ary network can achieve an error correction capability of (N − 1)(M − 1)/M digits, with a theoretical upper limit of (N − 1) digits, one digit short of 100%. This Substantial improvement comes at the cost of increasing the complexity of the feedback thresholding operation. An electroptical implementation of the model is described. The first component, an optical preprocessor, performs a Fourier transformation of the optical signal. This increases the tolerance for size and orientation discrepancies of the object. The second component is a CCD camera which transforms the 2-D optical signal into an analog electrical signal. The third component, a frame grabber, digitizes and stores the analog signal. The fourth component is a 16-bit Zoran digital signal processor (DSP) which performs the necessary calculations and the feedback thresholding operations required. The DSP under consideration would process forty images. Each image consists of 1024 M-ary digits (32 × 32 pixels). The processed signal is then projected onto a video monitor.
Narrowing the gap between physiology and perception: VEPs as a tool to study linking propositions
Authors: Dagnelie Gislin
Published: February 2023

The debate on the validity of linking propositions [Teller, Vision Res. (1984)] is complicated by a threefold gap: anatomical, between experimentally accessible neuronal structures and the unknown substate of perceptual states; philogenetic, between species whose physiology has been studied in detail and the single species whose mental states are verifiable; and paradigmatic, between approaches traditionally employed by the physiological and psychological communities. Visually evoked potentials (VEPs) have found application in the clinical field and in studies of human development. They also provide a challenging approach to the study of linking propositions.
Photonic shift register
Authors: Su S. F. , Koai K. T.
Published: February 2023

Optical memories are indispensable to time-division and self-routing photonic switching systems. Currently, optical fiber delay lines are commonly used as memory cells in such switching systems. These delay lines are fixed in length and not applicable to switching systems requiring flexible delays. To provide flexible delays, a directional coupler may be used in conjunction with a fiber delay line to form a reentrant delay-line memory.1 However, this delay-line memory has drawbacks too. First, the front portion of an optical pulse may escape from the delay-line fiber undesirably before the rear portion enters it, resulting in loss of part of the optical pulse and causing crosstalk between adjacent time slots. Second, changes of the directional coupler operation states must be precisely controlled; otherwise the loss and crosstalk mentioned above occur again. We propose a photonic shift register. It is designed using directional couplers, optical fibers, and passive optical combiners. A single-bit shift register may be used as an optical memory cell with flexible delay. A multibit register may be used as a photonic serial-to-parallel converter, a photonic parallel-to-serial converter, or a time slot interchanger. Design and operation of this photonic shift register are elucidated.
Wideband all-optical fiber-optic crossbar switch
Authors: Dias A. R. , Kalman R. F. , Goodman J. W. , Sawchuk A. A.
Published: February 2023

An all-optical nonblocking generalized fiber-optic-based crossbar switch is discussed. A classical matrix-vector multiplier architecture is the basis for a generalized nonblocking crossbar switch. This architecture is inherently parallel and capable of full broadcast. Its all-optical nature has two fundamental advantages. One is the inherent high bandwidth of optical circuits; the other is the minimization of electronic-optical and optical-electronic conversions in the interconnect circuit. The resulting switch has relatively high loss, making it of greatest interest for localized interconnects. Experimental results from two generations of crossbar switches based on this architecture are discussed of sizes 4×4 and 16 × 16, respectively. Technology issues regarding fan-in, fan-out, and shutters are reviewed. Specific applications in digital and analog interconnects are addressed.
Red-green zebra stripes in human foveal vision
Authors: Williams David R. , Sekiguchi Nobutoshi
Published: February 2023

Foveal aliasing causes high-frequency interference fringes to look like bright and dark (achromatic) zebra stripes. Some observers also report chromatic zebra stripes composed of desaturated red and green stripes. Two observers adjusted fringe spatial frequency and orientation to find the coarsest chromatic and achromatic zebra stripes. The coarsest chromatic zebra stripes occurred near the cone Nyquist frequency (57-64 cycles/ deg), half of the frequency producing the coarsest achromatic zebra stripes. The same fringe orientations, separated by ~60 deg, produced the coarsest chromatic and achromatic zebra stripes. Chromatic zebra stripes may be produced by a contrast-dependent color effect.1 At any instant, Nyquist frequency fringes produce local regions of high contrast (when cones are centered on fringe peaks and troughs) alternating with regions of low contrast (when cones lie between peaks and troughs). This could form red and green zebra stripes with hue determined by local contrast. An alternative hypothesis is aliasing by the M and L cone submosaics. If this hypothesis were correct, the data would constrain the packing arrangement of M and L cones. At least a subset of M cones would have to be packed in a triangular arrangement with the same orientation as the whole mosaic and with twice the spacing between rows of cones.
All-optical switching in a GaAs/AIGaAs strip-loaded nonlinear directional coupler
Authors: Jin R. , Chuang C. L. , Gibbs H. M. , Koch S. W.
Published: February 2023

All-optical switching has been demonstrated for the first time in a single-mode GaAs/AIGaAs strip-loaded nonlinear directional coupler (NLDC). The sample is grown by molecular beam epitaxy (MBE), and the guiding layer consists of sixty periods of GaAs/AIGaAs multiple quantum wells with 100-Å thickness for both the wells and barriers. The channels are formed by reactive ion etching of the top AIGaAs layer with a photoresist mask. The cleaved ends of the NLDC allow light to be end-fire coupled into the guides. A microscope objective with a numerical aperture of 0.65 is used to focus the light into the waveguides, and the output intensity profiles are monitored on an oscilloscope screen by means of a line scan. Linear cross coupling is observed at low input intensities, ~870-nm wavelength, and most light can be switched back into the input channel with a contrast ratio >3. Using picosecond pulses, the effect of carrier diffusion is negligible.
Single-beam squeezing in a Doppler broadened medium
Authors: Ho S.-T. , Wong Ngai C. , Shapiro J. H. , Kumar P.
Published: February 2023

We have generated squeezed states of light with a single pump beam propagating through Doppler broadened sodium vapor via forward four-wave mixing (FWM) with spatially degenerate pump and probe modes. The two probe-mode inputs are vacuum states at nondegenerate frequencies, which are transformed to squeezed vacuum by the FWM interaction. Compared with previous FWM configurations,1 this single-pass single-pump-beam configuration ensures maximal overlap of the four interacting beams, thus maximizing the squeezing nonlinearity and improving the overall efficiency. The transmitted pump has the wrong phase to act as the local oscillator for detecting the squeezed spectrum.1 Therefore, a cavity is used to filter out most of the transmitted pump intensity, and the squeezed vacuum is detected with another local oscillator using the standard dual-detector scheme. The residual pump beam provides a reference to monitor the phase between the pump and squeezed vacuum. The observed 0.8-dB reduction in the shot noise corresponds to an inferred 50% squeezing of the light at the exit of the vapor medium, which is in reasonable agreement with the theory given by Ho et al.
2
A linearly polarized pump is found to give less squeezing than a circularly polarized pump, possibly due to optical pumping.
Optimization of intracavity second harmonic generation in diode-pumped systems
Authors: Lin J. T. , Huang Y. L.
Published: February 2023

A model describing cw intracavity SHG of a diode-pumped system is presented based on a rate equation for the fundamental power inside the cavity given by where L1 and L2 are the linear (cavity absorption) and the nonlinear SHG loss of the cavity, G is the gain function proportional to the pumping rate and the transverse beam overlap function F. The nonlinear loss due to SHG is given by, including the pump depletion, L2 = 1- sech(y1) sech(y2), where y1 and y2 are proportional to the nonlinear coefficient of the doubling crystal and the fundamental power.
Analysis of signal and noise propagation for several imaging mechanisms
Authors: Rabbani Majid , Vanmetter Richard l.
Published: February 2023

We have previously shown1 that multivariate moment-generating functions provide a facile method for analyzing the influence of stochastic amplifying and scattering mechanisms on the transfer of signal and noise through multistage imaging systems. The method is general in that it can be applied to stationary as well as nonstationary processes. In the special case of stationary processes, relationships between the input and output noise power spectra (NPS) can be derived. For the case of photon-limited inputs, one can also readily express the detective quantum efficiency. We have extended application of the method to five cases of amplifying and scattering mechanisms in which the parameters are themselves stochastic variables and in which random variables are correlated between stages. Expressions for the NPS and DQE are derived for each case, and a physical example drawn from the study of radio-graphic intensifying screens is given. In several of these examples, previously published theoretical results have been shown to follow as special cases of these more general results.
Direct constrained linear associative memory inverse filter
Authors: Eichmann George , Stojancic Mihajlo
Published: February 2023

The recognition of signals and images degraded by a linear low-pass degradation operator, even in the absence of any measurement noise, is an ill-posed problem. Based on a new constrained associative memory (CAM) method, the reconstruction (restoration) for an arbitrary binary object from an image, either linearly degraded by a linear shift-invariant (LSI) or shift-variant (LSV) degradation operator, in the presence of strong noise, is achieved. Using an appropriate training set of signals, related ideally to a perfect degradation operator inverse, the CAM method yields a general, in the form of a 2-D array of coefficients, one-step impulsive-type (spiking) inverse filter. Computer simulation results of the reconstruction of 1-D and 2-D signals and images, degraded by LSI and LSV systems, in the presence of strong noise are presented.
Observation of polarization instabilities and chaos
Authors: Gauthier Daniel J. , Malcuit Michelle S. , Boyd Robert W.
Published: February 2023

We have observed that the polarizations and intensities of counterpropagating laser beams in sodium vapor are temporally unstable. The output from a stabilized dye laser tuned near to the 3S1/2 → 3P1/2 atomic transition was split to form the two counterpropagating beams. These beams were polarized with the same linear polarization and were weakly focused to a spot size of ~750 μm in sodium vapor having a density of ~3 × 1013 cm−3. We monitored the light generated in the polarization orthogonal to that of the pump beams. For a detuning of 1.01 GHz to the high-frequency side of the 3S1/2(F = 2) → 3P1/2(F = 2) transition and a power of 160 mW in one of the beams, we found that the threshold for the instability occurred at a power of 15 mW in the other beam. Slightly above threshold, the instability was found to be periodic in nature. As the intensity in the counterpropagating beam was increased far above the threshold value, wild fluctuations in the polarizations and intensities of the transmitted beams were observed. We have found that these fluctuations are chaotic and that the system evolves on a strange attractor whose dimension increases with increasing laser power. These observations are in qualitative agreement with the theoretical predictions of Gaeta et al.,1 which predict that the polarizations of counterpropagating beams in a Kerr medium are unstable to the growth of temporal fluctuations.
Enhancement of contrast sensitivity by microsaccades
Authors: Kelly D. H. , Burbeck Christina A.
Published: February 2023

Visual physiology suggests that the contrast sensitivity for a flickering or drifting grating should fall off sharply at temporal frequencies above 20 Hz (as in a typical DeLange curve). But when the spatial frequency of the stimulus is higher than 2 or 3 cycles/deg, the flicker response curve flattens unexpectedly beyond 20 Hz. Even with stabilized (drifting) gratings and careful fixation, our subjects detect such stimuli at frequencies as high as 200 Hz. We attribute this high-frequency sensitivity, not to a neural mechanism, but to the destabilizing effect of microsaccades. Similar microsaccade effects also appear to influence the thresholds for steady stabilized gratings.
Two-dimensional model for the vibrorotational transitions of a CO2 laser
Authors: Oppo Gian-Luca , Narducci Lorenzo M. , Tredicce Jorge R.
Published: February 2023

It is well known that a complete description of CO2 lasers requires the inclusion of the interaction between the resonant levels and the manifold of rotational levels that belong to the same vibrational state.1 Therefore, the phase space is enlarged to at least three coupled dynamic variables. However, experiments indicate that the dynamics is simpler and occurs in a 2-D subspace.
Photonics vs electronics technologies
Authors: De Maria Anthony J.
Published: February 2023

The history of the developments of electronics and photonics is briefly reviewed, and how these technologies interface with each other is reported. Examples of the uses of photonics technology are also given.
Rugate filters as minus filters
Authors: Pond B. J. , Carniglia Charles K.
Published: February 2023

Thelen1has developed a simple technique for improving the off-band transmittance of minus filters (or notch filters). This technique involves placing the filter between two substrates with reflective indices equal to the lowest index in the interference filter. Additional layers using the low index and an intermediate index are added on either side of the original layers to form a symmetrical structure. These antireflective layers improve the performance on both sides of the rejection band. A similar technique can be used if the structure of the filter is rugous, i.e., has a sinusoidal variation. Additional sinusoidal periods having an intermediate refractive index can be added on either side of the original rugate filter. The performance can be improved by proper choice of the intermediate index and the number of periods added. This design is somewhat simpler than a similar technique which has been proposed.2
Stark-induced phase modulation in coherent Raman spectroscopy
Authors: She C. Y. , Moosmuller H. , Krueger D. A.
Published: February 2023

In the early 1980s the influence of the optical Stark effect on vibrational and rotational transitions was investigated with coherent anti-Stokes and inverse Raman spectroscopies.1 For either an inhomogeneous intensity distribution in space or time, or molecules with several overlapping levels with different Stark coefficients, the Stark effect causes broadening and asymmetry in Raman1 and two-photon spectroscopies.2 However, if the inducing field is spatially uniform and temporally a Fourier-transform-limited pulse and if other broadening mechanisms can be neglected, the resulting spectrum should show a strong modulation due to an induced phase modulation in the molecular oscillation.
Quasielastic inverse power-law light scattering in fused silica optical fiber
Authors: Perlmutter S. H. , Shelby Robert M. , Levenson Marc D.
Published: February 2023

Quasielastic light scattering spectroscopy has long been used to probe the dynamics of thermal diffusion, sound propagation, and structural relaxation in condensed matter. Ordinarily the region around the zero frequency shift in such spectra is dominated by the Rayleigh line due to temperature/entropy fluctuations. Some materials, however, show an additional central peak attributed to structural or molecular relaxation processes.1,2 In a heterodyne detected backscattering experiment in cooled fused silica optical fiber, we have resolved a new relaxational light scattering component with a power-law spectrum and an unusual temperature dependence indicative of thermally activated kinetics. Previously reported measurements of light scattering in glass have had neither the sensitivity nor the resolution near 0 Hz to see either Rayleigh scattering or to resolve this new narrow central peak.2 At room temperature, the low-frequency light scattering spectrum is consistent with that predicted for conventional Rayleigh scattering. At lower temperatures, where the predicted Rayleigh scattering spectrum should decrease, we find that the light scattering actually rises. We interpreted these data using a modification of a model based on thermally activated kinetics in a system with a distribution of relaxation time constants.3 We are able to define the distribution of barrier heights for a local rearrangement of the fused silica matrix.
Numerical experiment of enhanced back-scatter by a phase screen
Authors: Welch Gisele , Phillips Ronald L.
Published: February 2023

An optical wave reflected back through a phase screen receives an enhancement of the average intensity along the line of incidence on the screen. This enhancement is due to single or multiple inhomogeneities depending on the mirror's position relative to the screen’s focus plane. Previous research has been mostly theoretical,1 although there have been some experimental2 studies. These studies confirm the existence of the phenomenon, but apparently no previous numerical study of this particular scattering mechanism has been performed. Organization of the numerical experiment constructed by simulating enhanced backscatter was derived as follows. A 2-D random phase screen was generated with a Gaussian phase shift for a 11/3 power-law turbulence spectra. A plane wave passes through the screen and propagates a distance z, at which point it encounters a mirror. The wave is then reflected back toward the initial screen. At the output of the second encounter of the same screen, the angular distribution of the power for the wave is analyzed along with the intensity fluctuations and the probability distribution of the intensity.
Refractive-Index structure parameter profiling system
Authors: Ochs Gerard R. , Wilson James J. , Lataitis Richard J. , Erl Noaa
Published: February 2023

The line-averaged refractive-index structure parameter

C
n
2

can be measured conveniently by observing the irradiance fluctuations of an incoherent light source with a receiver, where both the transmitter and receiver apertures are the same diameter and large compared to a Fresnel zone.1The measurement is most sensitive to

C
n
2

in the center of the path, tapering to zero weight at the ends of the path. The incoherent apertures form broad spatial filters that have a peak response to refractive-index irregularities having a spatial wavelength slightly larger than the aperture diameter. The weighting function may be shifted from the center of the path by using different diameter transmitters and receivers and by taking the difference of two transmitting or two receiving aperture signals. To avoid the effects of scintillation saturation, however, each individual aperture should be sufficiently large,1which restricts the filter complexity for an instrument of practical size. With these factors in mind, we developed a compact profiling instrument that measures

C
n
2

on three segments of an optical path between three-element transmitters and receivers.
Light-Induced Nonreciprocity: Directional Optical Bistability; Spectroscopy of Induced Anisotropy; Nonlinear Sagnac Effect
Authors: Kaplan A.E.
Published: February 2023

In our recent research1, it was suggested that counter-propagating laser beams in a Kerr-nonlinear medium can induce intensity-dependent nonreciprocity which consists in different changes of refractive indecies for both of the waves. Under some conditions, this can result in such directionally asymmetrical effects as (i) directional bistability in a nonlinear ring resonator which allows one to switch the direction of propagation of a dominant mode and (ii) enhancement of the Sagnac effect in a rotating ring resonator.
Nonlinear Optical Interfaces
Authors: Smith P. W. , Tomlinson W. J.
Published: February 2023

In this paper we will review the results of previous theoretical and experimental studies of nonlinear interfaces, and report new experimental results obtained using a liquid suspension of dielectric particles(1) as the nonlinear medium. This medium has a sufficiently large nonlinearity to permit nonlinear interface experiments to be performed with low-power CW laser beams, and thus simple, direct experimental verification of theoretical predictions is now possible for the first time.
Intrinsic Instabilities in Homogeneously Broadened Lasers
Authors: Hillman Lloyd W. , Boyd Robert W. , Krasinski Jerzy , Stroud C.R.
Published: February 2023

Experimental observation has shown that it is no simple matter to make a homogeneously broadened laser operate in a single longitudinal mode. However, elementary theoretical treatments of homogeneously broadening predict that such lasers can operate in only a single mode, because all of the atoms constituting the gain medium experience identical degrees of saturation.
Quantum Theory of Optical Excitonic Bistability
Authors: Gardiner C.W. , Steyn-Ross M.L.
Published: February 2023

A fully quantum mechanical formulation of the electron-hole-exciton-light system is developed following the work of Hanamura. In this formulation 1. The excitons are described by the "bosonisation transformation of Marumori et al. In this method exciton bose operators are introduced to describe electron-hole pairs, and anti symmetrisation effects are taken account of by a unitary transformation of the system operators, which introduces extra nonlinearities into the hamiltonian. This means that exclusion principle effects at high exciton densities are fully accounted for. The theory is formulated for Wannier (non-localised) excitons.
Optical Bistability in Semiconductors
Authors: Sung C. C. , Bowden C. M.
Published: February 2023

There are two different models to explain the observed optical bistability (OB) in GaAs. Haken and Goll1 use the saturation of the two-level (electron and hole) atoms as the mechanism of OB, whereas the Stark shift of excitons is the dominant factor in the work by Koch and Haug.2 We analyze both models, including the local field effect.3 It is shown that the validity of each model depends very much upon the parameters involved. We also give a similar analysis for CuCℓ where the biexcitons are important. In contrast to the earlier work by Abram and Maruani,4 we find by careful analysis, including the origin of the background dielectric constant, that the local field correction is not important in this case. The contribution of the exciton and biexciton interaction, however, can be important and should be included in the calculation of OB given by Haug.5 The changes in the numerical results of Ref. 5, by including the exciton-biexciton interaction and the local field correction are to be represented.
Bistable Operation of Two Semiconductor Lasers in an External Cavity: Rate-Equation Analysis
Authors: Dziura T.G. , Hall D.G.
Published: February 2023

This paper describes a theoretical analysis of the steady-state and transient behavior of a laser-with-saturable- absorber system consisting of two GaAlAs semiconductor laser elements in an external cavity.
Room-Temperature Thermal Optical Bistability in Thin-Film Interference Filters and Dye-Filled Etalons
Authors: Rushford M.C. , Weinberger D.A. , Gibbs H.M. , Li C.F. , Peyghambarian N.
Published: February 2023

Passive optical bistability in semiconductors was first seen in an interference filter with an intermediate layer of ZnS one-wavelength thick, and implied switch-on time of 200 μs.1 Thin-film interference filters may be potential practical bistable devices due to their room-temperature operation, extreme thinness, ease of production, and low-power operation.
Resonant Frustrated Total Reflection (FTR) Approach to Optical Bistability in Semiconductors.
Authors: Bosacchi Bruno , Narducci Lorenzo M.
Published: February 2023

The recent observation of very large non-linearities and of optical bistability in semiconductor structures at room temperature has heightened the interest in all-optical switching and signal processing as a practical prospect in optical information technology. Along with the search for suitable non-linear materials, some attention is also being paid to the study of structural configurations designed to optimize the performance of a bistable device. In this paper we will discuss the resonant FTR (Frustrated Total Reflection) approach, as an experimental configuration fully compatible with semiconductor and integrated optics technologies, which should lower the power requirements of a bistable device through the "enhancement" of the optical field inside its non-linear region.
Theory of Resonance-Enhanced Optical Nonlinearities in Semiconductors
Authors: Haug H.
Published: February 2023

In semiconductors the attractive Coulomb interaction between electrons and holes causes one- and two-photon resonances, known as excitons and exciton molecules, respectively. Large nonlinearities are observed in the spectral vicinity of these resonances. These nonlinearties are well-suited for the realization of optical bistability1),2),3) as has been demonstrated by Gibbs et al. 1)for GaAs and by Miller et al.2) for InSb. The electron-hole correlations, the screening and the energy renormalization are most conveniently calculated by the Green's function formalism. The optical dielectric function can be expressed in terms of the retarded photon self-energy which is also called the polarization function. This connection is not restricted to the linear response regime.
Optical Bistability with Two-Level Atoms
Authors: Kimble H. J. , Rosenberger A. T. , Drummond P. D.
Published: February 2023

Since the first observation of optical bistability in 1976 (1), a large number of investigations of this phenomenon have appeared in the literature (2). Of particular theoretical interest has been the bistable system composed of "two-level" atoms within an optical resonator. While the theory in this case is well-advanced, only recently have experimental results been obtained (3,4). The work that we report is for absorptive bistability with an intracavity medium that approximates a collection of two-level atoms.
Optical Bistability in CdS
Authors: Klingshirn C. , Fidorra F. , Bigot J.Y. , Wegener M. , Dörnfeld C. , Lambsdorff M.
Published: February 2023

Optical bistability (ob) is investigated in CdS in a wide range of intensities. Under pulsed excitation (total pulse width 20 nsec) we find at 5K for ħωexc ≈ 2.550 eV on the flank of the AΓ5 exciton ob of the induced absorption type for incident intensities of Iexc ≈ 1kW/cm2. The nonlinearity is in this case a collision-broadening of the free exciton resonance [1]. The commutation times τ↓ and τ↑ are about 1 nsec and 5 nsec, respectively. For ħωexc ≈ 2.546 eV we observe absorptive ob due to the formation of an electron-hole plasma [2] for Iexc ≈ 1MW/cm2. Single shot experiments show τ↓ ≲ 500 psec being thus to our knowledge one of the shortest commutation times reported for single beam ob so far. The observed hysteresis loops are compared to model calculations with variable pulse lengths. The comparison indicates true ob in our experiments.
An Ultrafast GaAs All-Optical Logic Gate
Authors: Migus A. , Antonetti A. , Hulin D. , Mysyrowicz A. , Peyghambarian N. , Gibbs H. M.
Published: February 2023

Optical bistable devices and logic gates have shown intriguing promise for optical computing of the future. Nonlinear semiconductor etalon devices have become increasingly popular for research on room-temperature switching at low powers with rapid response times. GaAs has displayed interesting advantages over other materials by operating at room temperature with a few milliwatts of power. In this presentation, the speed of a GaAs optical device is measured using femtosecond light pulses.1
Angle and Frequency Optical Bistability : Resonant Excitation of a Nonlinear Guided Mode
Authors: Arlot P. , Pic E. , Reinisch R. , Vitrant G.
Published: February 2023

We consider the system fig. 1. Its main feature is the existence of a Kerr substrate. Thus we deal with a nonlinear (NL) waveguide. The excitation process takes place through a prism.
Width of OB Switching Time Distributions
Authors: Arimondo E. , Gabbanini C. , Gozzini A. , Longo I. , Maccarrone F. , Mango F. , Menchi E.
Published: February 2023

In OB, if a control parameter is modified by a step-function so to reach a different transmission branch, the monitored output power reaches the new equilibrium value with a delay time τ. Owing to the intrinsic fluctuations or the noise in the apparatus the delay time does not have a constant value, but presents a distribution around the mean value <τ>. The distribution of the switching delay times has been measured in two OB experiments, involving, respectively, an infrared CO2 laser with intracavity saturable absorber and the microwave absorption of ammonia gas within a Fabry-Perot cavity.