bluuebunny/crossref_metadata_2025 huggingface dataset:
Operation of Integrated Semiconductor Optical Amplifier/Monitoring Detector with Feedback Control Circuit
Authors: Liou K.-Y. , Koren U. , Burrows E. C. , Oron M. , Miller B. I. , Young M. , Raybon G. , Burrus C. A.
Published: February 2023

Monolithic integration of a photodetector with a semiconductor optical amplifier simplifies the use of the amplifier in lightwave systems. Three important performance related characteristics: (1) output power leveling with a feedback loop, (2) gain optimization by input polarization control, and (3) anti-reflective (AR) coating of the amplifier facets, can all be controlled using the integrated detector as a monitor. We report in this paper an integrated optical amplifier/monitoring detector chip and its performance characteristics with a feedback control circuit.
Optical transmission characteristics of erbium fibre amplifiers in the 1.3 μm window
Authors: Farries M.C.
Published: February 2023

Measurements of the transmission of an erbium doped fibre amplifier between 1.05 μm-1.35 μm are reported. Excited state absorption at 1.14 μm and gain at 1.24 μm are observed.
Very-Low Threshold Loop-Mirror Switch Incorporating an EDFA
Authors: Richardson D.J. , Laming R.I. , Payne D.N.
Published: February 2023

All-optical switching devices based on ultra-fast optical non-linearities are of considerable interest for use in high-speed optical signal processing and telecommunications systems. Several switching schemes utilising χ(3) in optical fibres1-4 have been reported, but, although fast, they have large switching thresholds (100 -1000W) and suffer from environmental instability. Recent work5-7 has concentrated on the fibre Non Linear Optical Loop Mirror (NOLM) (or non-linear Sagnac interferometer), since the configuration is inherently a balanced interferometer and therefore environmentally stable. Consequently, longer fibre lengths can be used and the switching threshold reduced to 10-100W, a figure which is unfortunately still too high for practical application.
High Performance Erbium-Doped Fiber Amplifier Pumped at 1.48 μm and 0.97 μm
Authors: Zyskind J. L. , DiGiovanni D. J. , Sulhoff J. W. , Becker P. C. , Brito Cruz C. H.
Published: February 2023

With the growing importance of erbium-doped fiber amplifiers for telecommunications applications, considerable effort has been devoted to minimizing the pump power requirements for producing high gain. The best reported results are for λp = 0.98 μm wavelength pumping1,2 with gain coefficient up to 4.9 dB/mW, and for λp = 1.48 μm pumping,3,4 with a lower maximum gain coefficient of 2.6 dB/mW. We report here a low threshold erbium-doped fiber amplifier which, when pumped at 1.48 μm, has a gain coefficient is 5.9 dB/mW, and, when pumped at 0.972 μm, an almost equal gain coefficient of 6.1 dB/mW.
Soliton Transmission in a Distributed, Dispersion-shifted Erbium-Doped Fiber Amplifier
Authors: Nakazawa Masataaka , Kimura Yasuo , Suzuki Kazunori
Published: February 2023

Erbium-doped fiber amplifiers are very promising active components in the field of optical communication since they offer polarization-insensitive high gain, broad bandwidth, and low insertion loss [1]-[3]. There are two types of erbium fiber amplifiers. One is a lumped amplifier [1]-[3] and the other is a distributed amplifier [4], [5]. The distributed erbium amplifiers offer very attractive prospects for the realization of ultralong loss-less transmission lines. For example, they can be applied to optical soliton communication as we pointed out in an earlier paper [6]. To achieve distributed amplifiers of longer than 10 km, the doping concentration is decreased to as low as a few ppm.
Gain and Noise Characteristics of Er-doped Fiber Amplifiers with Different_Pumping Directions
Authors: Kakinuma T. , Takeda T. , Nishimura E. , Tamura Y.
Published: February 2023

We studied experimentally the gain, saturation power and noise figure of Er-doped fiber amplifiers for forward, backward and bidirectional pumping schemes with two types of Er-doped fibers.
Materials Considerations for Rare Earth Doped Glasses
Authors: Weber M. J.
Published: February 2023

Glass composition, codopant ions, and site-to-site variations affect and can be used to tailor the spectral and lasing properties of rare earth doped glasses.
Progress in Erbium Doped Fiber Amplifiers
Authors: Simpson J.R. , DiGiovanni D.J.
Published: February 2023

Erbium fiber amplifiers are entering a fourth year of development with six commercial offerings now available, the result of rapid improvements in pump lasers, wavelength division multplexers, isolators and doped fiber designs. A number of challenges remain however to improve the performance and ensure reliability in field applications.
Nd3+-doped Fluoride Fiber Amplifier Module With 10 dB Gain and High Pump Efficiency
Authors: Miyajima Yoshiaki , Sugawa Tomoki , Komukai Tetsurou
Published: February 2023

Recently, Nd3+-doped fluoride fiber has attracted much interest, because it has the potential for optical amplification around the 1.3 μm communication band[1]. In terms of the effect of ESA(excited state absorption) and the probability of radiative transition, fluoride fiber is preferable to silica fiber as a host glass[2], However, some problems must be solved for the development of a practical amplifier. First, gain has not been sufficiently large for a practical pump power to be obtained from diode lasers. Second, gain has been obtained in wavelengths longer than 1.31 μm.
Single-Mode, 980 nm Pump Lasers for Fiber Amplifiers
Authors: Crawford F. D. , Sharfin W. F. , Elman B. , Lauer R. B. , Mebrahtu P. , Eichen E.
Published: February 2023

Pump lasers for Er3+-doped silica fiber optical amplifiers must demonstrate excellent spatial mode stability to high output power levels in order to achieve useful gain.1,2 The pump band at 980 nm is the most efficient of the principle Er3+ absorption bands in terms of gain per input optical power.3 Pumping at 980 nm is also preferred in comparison to pumping at 1480 nm because it reduces the noise introduced into the amplified optical signal.4
Gain Characteristics of Lanthanum Co-Doped Erbium Fiber Amplifier
Authors: Kimura Yasuo , Nakazawa Masataka
Published: February 2023

Recent progress on erbium-doped fiber amplifiers (EDFAs) and their application to optical communications has been very rapid since the EDFA has many advantages such as polarisation-insensitive high gain, a low noisefigure, and low insertion loss.1 It is well known that in order to obtain a broader and relatively flatter gain profile, Aluminum (Al2O3) is co-doped into the core of the fibers.2,3 To make a wavelength independent flat gain profile is very important from the viewpoint of ultrashort pulse amplification and wavelength division multiplexing technique. Payne and Laming investigated a Borolanthanate co-doped EDFA.4 Although LaF3 or La2O3 were used as hosts for Nd ions5~7, detailed gain characteristics of a Lanthanum co-doped Er/SiO2 fiber amplifier have not yet been clarified.
The future role of semiconductor optical amplifiers
Authors: Marshall I.W.
Published: February 2023

The recent rapid development of Erbium doped fibre amplifiers with high gains, high saturation powers and low noise figures [1,2] has deflected the attention of system engineers from the older semiconductor technology [3] and it is thus now hard to find new published papers which use semiconductor amplifiers in a system context. Device development has not ceased however [4] and the performance of semiconductor amplifiers has improved considerably. In addition there are important applications for which doped fibre amplifiers are not suitable at present e.g. at 1.3 µm, and others for which they will never be suitable, e.g. as fast optical switches. This presentation attempts to review these possibilities for future practical application of semiconductor optical amplifiers in the light of the recent developments of the technology.
Optical Fabrication Using Ion Beam Figuring
Authors: Wilson S.R. , Barron A.C. , McNeil J.R.
Published: February 2023

The application of ion beams to the figuring of optical surfaces has been examined for a number of years by several groups of investigators. The technique is generally intended to perform the final figuring of surfaces which have several optical waves of error relative to the desired figure. Until recently, ion beam figuring has not offered promise to be an efficient, practical method for figuring optics.
All-Metal Resonator Designs for Visible/Near-Infrared Free-Electron Laser Oscillators*
Authors: Newnam Brian E.
Published: February 2023

The multiple radiation environment of future high-current free-electron laser (FEL) oscillators will pose severe requirements on the resonator mirrors. In addition to withstanding the high-average power, high-repetition-rate pulses of the fundamental laser radiation, the optical properties of the mirrors must not be degraded by the attendant optical harmonics, gamma rays, neutrons, electrons, and vacuum. Furthermore, the initial mirror absorption must be low enough so that the reflected wavefront distortion is tolerable when various types of mirror cooling are employed.
Oblique incidence resonances in metal-dielectric thin-film-structure energy conversion systems
Authors: Macleod H. A.
Published: February 2023

The admittance diagram is a useful device for visualizing performance of dielectric and metal-dielectric structures with small or negligible losses. Admittance can readily be converted into reflectance by a set of isoreflectance circles that is a function of the admittance of the incident medium. Difficulties are caused by the variation of admittance with angle of incidence because the isoreflectance circles are not constant but vary both with angle of incidence and plane of polarization. A simple scheme of admittances in which the incident medium is normalized to be constant at its normal incidence value is straightforward and permits the isoreflectance circles to remain constant. The scheme involves multiplying the normal p-admittance and dividing the s-admittance by cosθ0 where θ0 is the angle of incidence in the incident medium. This normalization does not affect either reflectance, absorbance, transmittance, or phase changes. Resonances such as those associated with coupling to a surface plasmon become straightforward to visualize including some involving metal-dielectric multilayers.
Optical monitoring techniques for multilayer films
Authors: Goldstein Fred
Published: February 2023

It is possible to improve optical coating yields in existing vacuum chambers. Reflectance (or transmittance) monitor signals obtained in the deposition of low-index materials are substantially increased through utilization of multilayer witness techniques. Accuracy is enhanced by terminating layers in regions where signal changes are rapid with respect to optical thickness. In most applications, a highly interactive special purpose computer program based on Rouard’s method is utilized for translating thin-film designs into optical and crystal monitoring parameters. The program converts design optical thickness to physical thickness and reconverts to chamber optical thickness. Numerical and graphical output is expressed in terms familiar to coating technicians. There are a number of cases in which a more general program is utilized: absorbing films, high angles of incidence, and high number of layers where the nonmonochromaticity of the analyzing light must be taken into account. A color contour plot provides an over-view of monitor response vs wavelength. This program also includes ellipsometric output in optical monitor format: Psi and Delta plotted separately as a function of physical thickness.
Computer-generated holograms of 3-D objects composed of lines
Authors: Leseberg Detlef , Frère Christian , Bryngdahl Olof
Published: February 2023

The generation of holograms using a computer offers flexibility for data storage and display. The major problems, however, are the calculation of the optical field in the hologram plane, which is usually performed by a simulation of the wave propagation between the object and the hologram planes and the coding of complex values into a real transmittance. To calculate the field, the algorithms most often used are the fast Fourier transform and the Fresnel zone plate. Both of them assume a decomposition (sampling) of the object into points (pixels). This implies limitations, e.g., in the overall number of object pixels. To overcome this, a procedure is suggested using lines of finite length as the basic elements. The wave propagation is described analytically for arbitrary orientations and lengths of the line segments and a wave propagation toward the hologram. The result is a conical wave which is coded in the hologram by calculating the superposition of an in-line reference wave. Optical reconstructions demonstrate the feasibility of the procedure.
Multimode instabilities in a homogeneously broadened ring laser
Authors: Bandy D. K. , Narducci Lorenzo M. , Sadiky H. , Lugiato L. A. , Tredicce J. R.
Published: February 2023

In addition to the well-known multimode instability predicted in Refs. 1 and 2, a homogeneously broadened laser can display another type of multimode unstable behavior stemming from a different physical origin. This new type of behavior is associated with the development of positive real parts in the phase eigenvalues of the linearized problem, and manifests itself through the competitive action of neighboring cavity modes as one varies the detuning parameter. This type of phase instability can be the cause of regular output pulsations or hysteretic behavior of the bistable type in the output intensity and in the laser operating frequency. In this presentation we discuss the theoretical background of the effect, identify the physical conditions that may support regular oscillations or bistability, and investigate the interplay between the amplitude instability of Refs. 1 and 2 and the present type of unstable behavior.
Model-based image enhancement for the visually impaired
Authors: Peli Eli , Arend Lawrence E. , Timberlake George T.
Published: February 2023

Image enhancement potentially provides low-vision patients better use and enjoyment of printed photographs and TV. A variety of equipment and techniques exist for enhancements, but there is no systematic method of designing appropriate enhancement for low-vision patients. Most image enhancement techniques may be classified as either contrast modification or spatial-filtering techniques. Although global contrast modification may be beneficial for the visually impaired, there is no way to optimize the selection of the modification paradigm or the parameters to be used. We propose a linear model of impaired vision in which the degradation transfer function resulting from the impairment is described by the ratio of the spatial contrast sensitivity function (CSF) of the low-vision eye to the CSF of a normal eye. The inverse of the degradation transfer function may be used as a spatial filter to preemphasize the image before it is displayed to the low-vision patient. Based on the CSF, the appropriate filter may be tailored for each patient or group of patients. Both threshold and suprathreshold CSF data may be required for the filter design. Results with optically simulated cataracts indicate that this approach may be feasible for patients with high spatial frequency loss.
Optical observation of geosynchronous satellites and laser beam transmission from a ground station
Authors: Aruga Tadashi , Araki Kenichi , Itabe Toshikazu , Hayashi Risao
Published: February 2023

We report experimental results for optical observation of geosynchronous satellites and for earth-to-geosynchronous satellite laser beam transmission, where the Japanese Geostationary Meteorological Satellites, II, III (GMS-II, III) have been used. In the former, two activities, (1) orbit prediction (from microwave ranging) correction using optical tracking data, and (2) optical observation of the scene during the time of apogee motor firing of the GMS, are reported. In these experiments, a compact optical system composed of a 50-cm diam Cassegrain telescope and SIT camera was used. The results of (1) indicate that orbit prediction of geosynchronous satellites obtained from microwave ranging, which has an error of ~0.01° order, can be corrected to an order of ~0.001° using optical observation data. In experiment (2) the jet gas diffusion in geosynchronous orbit space was clearly observed. In the latter, the VISSR (visible and infrared spin scan radiometer) on board the GMS was used for detecting the laser beam transmitted from a ground station. At first an argon laser (wavelength = 0.5145 μm) was used as the cw transmitter. A clear spot image of the laser beacon was detected with good SNR against the earth’s background. Then we tried CO2 laser (10.6-μm) beam transmission.
Nonlinear inversion method applied to atmospheric infrared spectra from Spacelab
Authors: Brard D. , Laurent J.
Published: February 2023

We have developed an automatic iterative process for retrieving vertical concentration profiles of atmospheric gases from a set of solar absorption spectra with different tangent heights, using a multilayer atmospheric model.
Diffractive theory of the aberration sensitivity in an unstable resonator
Authors: Oughstun Kurt E.
Published: February 2023

A diffractive formulation of the aberration sensitivity of a positive branch, confocal unstable resonator is presented. The kth-order aberration sensitivity coefficient is found to be given by

α
¯

k

≅

α
¯

k

(
0
)

⋅

Γ

k
⋅

The factor

α
¯

k

(
0
)

=

ψ
k

/
(

M
k

−
1
)

describes the aberration sensitivity behavior in the absence of any change in the cavity mode eigenvalue. The associated eigenvalue change due to the intracavity aberration source is accounted for by the factor Γ
k
. The geometric factor ψ
k
accounts for the double interaction of the cavity field with the aberration source in a single round-trip propagation through the cavity. Within Ananev's geometric approximation, ψ
k
is readily obtained from the unperturbed ray geometry of the geometric cavity mode structure. The analysis presented here includes the deviation of the ray trajectory due to the aberration source. This new analysis then yields the dependence of the aberration sensitivity coefficient on the applied aberration source strength. The diffractive expression for the aberration sensitivity is shown to increase to its geometric value as the Fresnel number of the unstable cavity is increased, this increse being more rapid for larger transverse aberration order k.
Observation of phase-sensitive noise in sodium vapor
Authors: Maeda Mari W. , Kumar Prem , Shapiro Jeffrey H.
Published: February 2023

Squeezed states of light exhibit phase-sensitive quantum noise measurable via optical homodyne detection. They have been predicted to be generated via degenerate four-wave mixing, resonance fluorescence, and nonlinear propagation.1 We report observing phase-sensitive noise via optical homodyning on a cw dye laser beam which has propagated through sodium vapor near the D lines. A p-polarized dye laser beam of ~5-W/cm2 intensity was passed through sodium vapor near its D lines. Homodyne measurements were made on both the s- and the p-polarized components of the transmitted beam using the dual-detector subtraction scheme.2 A spectrum analyzer monitored the noise in a 6–15-MHz band. In the absence of sodium, the noise in this band was vacuum-state quantum noise limited and was insensitive to the relative local-oscillator beam/transmitted laser beam phase θ. In the presence of sodium, the noise was sensitive to θ, with dependence of the form As,p + Bs,p cos2(θ − ϕs,p), where ϕs = 0 for s polarization and ϕp = π/2 for p polarization. For one set of data we measured As = 2 dB, Bs = 3 dB, Ap = 3 dB, and Bp = 2.5 dB above the noise levels in the absence of sodium. The s-poiarization data were collected with the local-oscillator power PLO far in excess of the s component of the transmitted pump power PTP; for p polarization, PLO ~ PTP prevailed. The measurement uncertainty in the spectrum analyzer data is ±0.5 dB. Possible physical mechanisms to explain these results are discussed.
Current status of squeezed light generation
Authors: Walls D. F. , Reid M. D.
Published: February 2023

We review current theoretical and experimental work on squeezed light generation.1 Quantum treatments of four-wave mixing using a two-level atomic model and an anharmonic oscillator model of the medium are presented.2 The results are compared with experiments on four-wave mixing in atomic sodium3 and optical fibers.4 Methods to suppress spontaneous emission noise are discussed.
Interaction between lateral and eccentricity-dependent preferences in saccadic responses
Authors: Hason B. , Zeevi Y. Y.
Published: February 2023

Eye movement responses to dual targets provide insight into mechanisms of visual information acquisition. It was previously shown1 that symmetric point targets stimulating both hemispheres require extra processing time compared to either a single or a dual unidirectional stimulus. These so-called bifurcating point stimuli reveal the existence of preferred lateral direction. We substantiate and refine these results incorporating the effects of eccentricity. In the case of a unidirectional dual target an absolute preference exists for the target closer to the fovea. Responses to asymmetric bihemifield stimuli show that the lateral direction preference is contingent on target eccentricities. Being close to the fovea enchances, whereas being away from the fovea inhibits, the preference level of the point target. If one of the points is delayed, the overall lateral, spatial, and temporal preferences determine the response direction. At large interpoint delays for which the second point is still the preferred one, the response time measured with respect to the onset of this target is much shorter than the average latency. We propose a stochastic model accounting for the temporal aspect of our observations. Each point stimulus is processed in a separate channel in two stages, the first providing a general intermediate output utilizable in the processing of any additional input. Interaction between opposite hemispheric channels results in longer response duration due to the second stage processing time. The model reproduces the timing of events in responses to dual targets.
Mechanisms for the detection of flicker and motion
Authors: Bergen James R. , Adelson Edward H.
Published: February 2023

The findings of Levinson and Sekuler1 and of Watson et al.2 suggest that flickering gratings, which can be represented as a sum of two moving gratings, are detected by two independent rightward and leftward sensitive motion mechanisms. However, the recent work of Stromeyer et al.3 shows a failure of this independence above absolute threshold and points to a motion opponent mechanism. To further investigate these issues, we have been exploring the space of stimuli consisting of sums of rightward and leftward moving gratings, of equal spatial frequencies and speeds, but with varying contrasts. We can represent these stimuli by plotting the rightward and leftward component contrasts on vertical and horizontal axes. In this space, points on the diagonal correspond to counterphase flickering gratings, while those along the axes correspond to single moving gratings. Other points in the space represent mixtures of flicker and motion. We have measured discrimination thresholds in the various possible directions in this space around points on the axes, on the diagonal, and in the regions between. These thresholds define contours somewhat analogous to ellipses of confusion in color discrimination. The data cannot be fit with existing motion models. We present a model in which two kinds of mechanism (opponent motion detectors and counterphase flicker detectors) operate in parallel. These detectors consist of energy extracting mechanisms like those described by Adelson and Bergen4 followed by static nonlinearities.
Laser-modulated transmission in GaAs doping superlattices
Authors: Simpson T. B. , Leavitt R. P. , Simonis G. J. , Winter J. J. , Anthony J. E. , AuCoin T. R.
Published: February 2023

The doping superlattice1 consists of thin alternating layers of n- and p-doped semiconducting material. The electric field induced by carrier migration leads to band bending and to an indirect band gap in real space. The energy of this indirect band gap can be tuned by creating electron–hole pairs by means of laser excitation, thus changing the transmission, reflection, and photoluminescent properties of the superlattice. GaAs doping superlattices having various layer thicknesses and dopant levels were grown by means of molecular beam epitaxy. Optical properties of the samples were measured at temperatures ~300, 80, and 5 K. Modulation of the optical properties by an exciting Ar laser was strongest at 5 K and too small to be observed at 300 K. At 5 K, under appropriate laser excitation, photoluminescent peaks were shifted toward longer wavelengths, as far as 9300 Å. Laser-modulated absorption was observed from 8250 Å, corresponding to an energy slightly less than the GaAs direct band gap, to 8900 Å. The experimental results are compared with theoretical calculations of properties of doping superlattices.
Optimization of the photoyield of platinum silicide Schottky barrier diodes
Authors: Mooney Jonathan M. , Dereniak Eustace L.
Published: February 2023

Measurements of the reflection and transmission in the mid-infrared of varying thicknesses (5400 Å) of platinum silicide films on silicon substrates are presented. The data are used to calculate the absorption and optical constants (n,k) of the thin films; the optical constants are then used to determine the structure of the optical cavity required to optimize the absorption of the metal film. Finally, a model for internal photoemission is combined with the calculated absorption measurements and the structure is reoptimized to determine the cavity structure required for greatest photoyield.
Optical diffraction characteristics of the variable grating mode liquid crystal device
Authors: Wu C. S. , Tanguay A. R. , Johnson R. V.
Published: February 2023

In the variable grating mode (VGM) liquid crystal device (LCD), a birefringent optical phase grating is generated by a dc bias voltage. The spatial frequency of the grating is observed to vary linearly with the applied voltage. The VGM LCD exhibits quite unusual polarization effects in the various diffraction orders.1 Although the device is fairly thin (~6 µm), the strong natural birefringence of the liquid crystal medium makes anisotropic diffraction effects significant. For the VGM LCD the odd and even diffraction orders exhibit strikingly different angular alignment sensitivity characteristics as a function of the incident light beam angle. The observed results suggest that the even diffraction orders can be interpreted in terms of a simple isotropic Raman-Nath diffraction model, whereas the behavior of the odd diffraction orders is characteristic of Bragg regime anisotropic diffraction. An analytic model of the liquid crystal molecular orientation as a function of spatial coordinates, the applied electric field, and the surface constraints has been developed. A numerical method for the analysis of anisotropic optical beam propagation through volume grating media, described in an accompanying paper, is used to simulate optical propagation through a thin VGM device and to predict the resultant optical diffraction characteristics.
Molecular infrared coherence transfer kernels by scale transformation of photon echo decay data
Authors: Thomas John E. , Liang Jeng-Min , Spinelli Louis S. , Dasari Ramanchandra R. , Feld Michael S.
Published: February 2023

Experiments exploiting similarities for coherence collisional evolution in velocity space and in M space are reported. Generally, there is a total outgoing rate from any state and incoming rates (kernels) from neighboring states. Collision-induced velocity changes, ΔV, are studied with lasers by measuring the Doppler frequency Δ V/λ (λ = optical wavelength). To obtain information about coherence M transfer, it is only necessary to associate a frequency with each ΔM. This idea is demonstrated by measuring two-pulse photon echo intensity Ie for 13CH3F in a small dc Stark field. Acoustooptic modulation of infrared cw laser radiation, polarized parallel to the Stark field, is used to excite a number of uncoupled M → M transitions on the R(4,3) line. Each transition has a resonance frequency, vo + M· vs (vs is M = 1 Stark shift, Hz). A most remarkable result is obtained for large echo delays T with ΔVT/λ >> 1, all ΔV. The shape of the curve ln[ Ie(o)/ Ie(V)] vs Stark voltage V tends to that of the dominant coherence ΔM transfer kernel itself. Physically this arises because, for large T, the macroscopic coherence is preserved only for collisions where the frequency changing due to M transfer compensates the Doppler shift due to the ΔV, i.e., Δ V/λ + ΔM-·vs = 0. Generalizations are discussed.
Photothermal studies of nonradiative energy loss in dilute dye solutions
Authors: Lee Wing-Kee , Gungor Ali , Davis Christopher C.
Published: February 2023

Single-frequency laser heterodyne measurements in a modified Jamin interferometer have been used to study the nonradiative energy loss of isolated rhodamine 6G molecules in solution. Pure methanol and several methanol-based solvents containing the quencher potassium iodide were studied. Simultaneous measurement of both the fluorescent intensity and the photothermal phase modulation induced by AM argon-ion laser excitation allows absolute determination of both the quantum efficiency η and the fraction of absorbed photoenergy converted to heat. Broadband fluorescent intensity was measured with a photodiode. Photothermal phase modulation was synchronously detected by operating the Jamin interferometer in quadrature and passing the resultant linear intensity modulation to a lock-in amplifier. Rhodamine 6G concentration as low as 5 × 10−9 g/m liter could be used. Typical Kl quencher concentrations were in the 0.33-4.5-mg/m liter range. The absolute quantum efficiency of rhodamine 6G at zero quencher concentration was found to be 96 %. The fraction of absorbed energy converted to heat at zero quencher concentration was 12%.
Hyperacuity performance as a function of contrast
Authors: Olzak Lynn A. , Thomas James P.
Published: February 2023

In many discrimination tasks, performance becomes independent of contrast at very low contrast levels. In this study, we examine performance in a hyperacuity discrimination task (bisection) as a function of contrast level. The stimuli were three parallel vertical lines superimposed on a 34-cd/m2 uniform field. On any given trial, the center line was offset either to the right or to the left by a single fixed distance. The offset was chosen to yield a d' of~1.7 at the highest available contrast level. Observers rated, on a 6-pt. scale, their certainty that the line was offset to the left (a rating of 1) or to the right (a rating of 6). The lines were always brighter than the background and could appear at one of eight contrasts spanning the range from threshold to ~80 %. In any block of 100 trials, only a single contrast value was used. Each day, four contrast levels were run in counterbalanced order. The z transform of the area under the ROC curve was used as a measure of performance and plotted as a function of contrast level. The results provide some information about which spatial frequency components are important in determining performance in the bisection hyperacuity task.
Does 2-D spatial hyperacuity exist?
Authors: Meer Peter , Zeevi Yehoshua Y.
Published: February 2023

In most spatial hyperacuity tasks, a measure of relative position can be computed, when superior precision for just one spatial coordinate is available. We have designed a 2-D nonalignment task wherein subjects have to localize a dot relative to the virtual intersection of vertical and horizontal directions defined by two line segments. This task can be executed if and only if the subject extracts both spatial coordinates of the dot with hyperacuity precision. The lines were 15 min of arc long and separated from the dot by gaps of 8 min of arc. A 4AFC measurement paradigm (top-left; bottom-right, etc.) was employed. Short stimulus presentation time (200 ms) resulted in 2-D nonalignment thresholds exceeding 25 s of arc, clearly above the hyperacuity range. The thresholds were significantly improved for long stimulus duration (2000 ms), when a sequential processing strategy was presumably employed. The same results were obtained by employing a different, 2AFC (staircase) measurement paradigm. In a control experiment, Vernier acuity did not present significant improvement with presentation time. We conclude that spatial hyperacuity tasks have access to a limited processing capacity of the visual system. The results further emphasize the importance of the comparison process previously concluded from perturbation experiments.1
Experimental measurements of the nonlinear dynamics of a laser with an injected signal
Authors: Fisch E. E. , Abraham Neal B. , Hoffer L. M. , Gioggia R. S.
Published: February 2023

A unidirectional ring laser operated on the 3.51-μm transition in xenon has been studied for its behavior under injection of a constant intensity signal from a separate single-mode laser. The combined output variously shows simple beating (heterodyne mixing of the two lasers in the infrared detector) and more complicated nonlinear interactions that lead to pulsations and locking. Nonlinear interaction is indicated by the appearance of harmonics of the free-running laser beat frequency which result in nonsinusoidal intensity pulsations. A stronger indicator of the nonlinear interaction is found in the heterodyne spectrum where we see clear evidence that the injected signal is joined by a new optical frequency component symmetrically located with respect to the ring laser frequency. The degree of nonlinear interaction depends principally on the frequency difference between the two initial frequencies of the free-running lasers. The strength of the injected field also helps to determine the exact nature of the interaction. As the degree of homogeneous broadening of the xenon transition can be varied with the buffer gas (helium) pressure, various parameter-dependent details of the system have been determined for comparison with recent theoretical and numerical results.
Deterministic approach to intracavity adaptive-optic mode control
Authors: Oughstun K. E.
Published: February 2023

A deterministic approach to intracavity adaptive-optic mode control based on the geometric theory of the aberration sensitivity in unstable resonators is described. This approach relies on a direct measurement of the phase aberration structure outcoupled from the resonator from which is determined a global estimate of the required correction. The results of a numerical simulation of this correction procedure in an unstable’ laser system for several aberration types are presented. In all cases considered, the residual intracavity phase aberration is driven to zero in four iterations of the described correction scheme, while the relative far-field performance measures of on-axis intensity and absolute power in the bucket are driven to within 1 % of their unaberrated values in just three iterations.
Optical beam shaping of a high power laser
Authors: Dagenais Dominique M.
Published: February 2023

The objective of this work was to develop a technique for converting a high power laser beam with a nonuniform intensity distribution into a rectangular image with a uniform top, trapezoidal intensity profile. Uniformity of the fluence distribution delivered from a laser to a working plane is a requirement in many applications such as metal heat treatment, laser function, laser radar. We describe a specific design, constrained by its application to automated laser paint stripping, but the concept is of general applicability. In our case, paint stripping requires a 10% fluence uniformity on target and an edge roll-off for effective traverse overlap. The high levels of laser power involved require an all-reflective system with no primary or secondary focusing of the beam. The high degree of uniformity involves combining a multimode laser with an optical beam shaper. We present the design concept of the beam shaper and the theoretical image intensity distribution. We also show the experimental verification of the concept using a multimode CO2 laser beam and discuss the resulting IR images obtained.
Photofragment fluorescence as an analytical technique: application to gas-phase alkali compounds
Authors: Oldenborg Richard C. , Baugh-Cum Steven L.
Published: February 2023

Photodissociation of gas-phase compounds using a laser at suitably short UV wavelengths can produce electronically excited photofragments. Detection of fluorescence from these excited fragments, particularly atomic fragments, allows sensitive and quantitative density measurements, while signal strength as a function of dissociation laser wavelength allows differentiation among compounds that yield the same photofragment. Sensitive techniques are needed for the detection of highly corrosive gas-phase alkali compounds in the combustion of coal gas to drive gas turbines. We present here an evaluation of photofragment fluorescence based on the results of experiments to study the photodissociation of the chlorides and hydroxides of sodium and potassium. Alkali compound vapors were irradiated at 193 nm from an ArF laser and other wavelengths generated by stimulated Raman scattering. Fluorescence from electronically excited alkali atoms in the lowest 2P0 level was observed, and the dependence of the fluorescence intensity on temperature, was investigated. The atomic emission intensities quantita-tigated. The atomic emission intensities quantitatively track the density of the alkali compounds over a wide dynamic range, and detection at sub-part-per-billion concentration levels is readily achievable. Discrimination among different compounds of the same alkali metal based on the dissociation laser wavelength dependence is also discussed.
Launching light into rooftop fibers and its effect onintermodal dispersion
Authors: Sunak Harish R. D.
Published: February 2023

The launching efficiency (η) from semiconductor lasers into plane-ended (PE) multimode fibers is low(~10 20%). We polished PE into rooftop (RT) ends, having a RT angle of 65° to the fiber axis, and observed a substantial increase in η; 27% (PE) to 51 % (RT). This was achieved (ηmax) after optimizing the apex position of RT fiber with respect to the stripe; the two have to be parallel. When they were perpendicular, ηmin = 29% was obtained. The effect of longitudinal, lateral, and angular misalignments was compared for the PE and RT ends; the latter were always more critical. We further investigated, for the first time, the effect on the intermodal pulse dispersion and obtained the following results: (i) output FWHM after 1 m having PE or RT end was 0.57 ns, (ii) FWHM after 1 km with PE input was 0.70 ns, giving pulse dispersion (t
m
) of 0.41 ns, (iii) FWHM after 1 km with RT input and r/max was 0.61 ns giving t
m
= 0.22 ns, (iv) FWHM after 1 km with RT end and ηmin was 0.65 ns giving t
m
= 0.31 ns. The material dispersion was negligible. Hence comparing (ii) and (iii) above, t
m
was reduced by a factor of 2. This was explained by alteration of the modal power distribution in fiber core and confirmed by output far-field measurements.
Forward optical glory of bubbles in liquids: theory and observations
Authors: Langley Dean S. , Marston Philip L.
Published: February 2023

We have photographed the near-forward crosspolarized scattering pattern from individual bubbles and from bubble clouds in liquids. The bubbles were large in comparison to the wavelength of light. The quasi-periodic structure present for individual gas bubbles is similar to that previously observed for the cross-polarized near-backward glory of bubbles.1,2 The observed periodicity is in good agreement with a calculation of diffracted glory wave fronts and it is clearly not caused by the ordinary forward diffraction which is copolarized with respect to the illumination. The gas bubbles observed were in water or in silicone oil. The dominant glory wave was associated with the twice-refracted (once-reflected) ray. Although these experiments may be interpreted using a theory which assumes single scattering, the observed polarization phenomena may be helpful in the understanding of scattering from dense bubble clouds where multiple scattering may be significant. The polarization and structure of glory scattering may be useful in inverse problems.
Rotationally invariant correlation filtering for multiple images
Authors: Schils George F. , Sweeney Donald W.
Published: February 2023

Numerous problems in optical pattern recognition require the classification of a finite number of images regardless of their orientation angles. A method is presented for designing translationally invariant optical correlation filters that produce a specified response to rotations of each of the input images. The correlation filter is formed as an infinite linear combination of the angular Fourier harmonics of the n input images. Imposing the requirements for the specified rotational response of the filter to each input image leads to a vector-matrix convolution equation that is to be solved for the unknown angular weighting coefficients. Expansion into vector-matrix angular Fourier series and term-by-term solution for the Fourier coefficients gives a number of systems of n equations for n unknowns. The elements of the matrix describing each system of equations are the correlations between the angular harmonics of the input images. Inverting this matrix decorrelates the angular harmonics of the input images and allows an arbitrary response to be obtained. Choosing the special case that the rotational responses consist of only one nonzero Fourier series coefficient gives the generalization of the circular harmonic filter to n images. We call this the multiple circular harmonic filter. The classification of n input images can be achieved by choosing the rotational response amplitude to be a different constant value for each image. As shown by examples, this allows multiple input images to be distinguished while preserving rotational invariance.
Real-time polychromatic signal detection by matched spatial filtering
Authors: Yu F. T. S. , Javidi B.
Published: February 2023

Experimental results for a real-time polychromatic pattern recognition system are presented. In this technique, image recognition is performed based on both the spectral content and the shape of the target which can be a diffusely illuminated real object. The correlator employs a color encoding grating and a spatial light modulator to convert the incoherently illuminated color object into spatially sampled coherent images to be processed by a multispectral band matched spatial filter. The advantage of this system over the prior matched filtering technique is its ability to use both color and shape in recognizing real objects. Experimental results obtained by this real-time correlator indicate that the system has a high degree of color-spatial selectivity.
Oblique and meridional effects in peripheral vision
Authors: Walsh David J. , Thibos Larry N.
Published: February 2023

Central acuity is worse for oblique gratings than for vertical or horizontal and this effect is said to extend some 18° into the periphery as well.1 However, quite a different phenomenon has also been described for peripheral vision, the meridional effect, which is characterized by greater acuity for gratings parallel to visual meridia than for the other orientations.2 As these two generalizations are inherently incompatible, we sought to determine which effect prevails. Acuity was determined as a function of grating orientation for the eight primary meridia at six eccentricities in the 10-35° range. Results revealed that either effect may dominate, depending on the particular visual field location, stimulus configuration, and subject. Some individuals show an oblique effect for all eccentricities while others show a transition from the central oblique effect to a meridional effect in the periphery. Furthermore, these two patterns can occur for different meridia in the same individual and may sometimes be altered significantly by varying the luminance of the field immediately surrounding the test grating. Despite this variety of results, the body of our data can be accounted for by supposing that two forces shape the orientational anisotropy of peripheral vision. Just which force is the stronger depends on numerous factors and cannot be summarized yet by a simple generalization.
Theory of pump-wave propagation and its effect on degenerate four-wave mixing
Authors: Gruneisen Mark T. , Gaeta Alexander L. , Boyd Robert W.
Published: February 2023

We have derived an analytic expression for the intensity distribution of two counterpropagating waves of arbitrary input intensity in a saturable absorber. We use this distribution to extend the theory of degenerate four-wave mixing to include the effects of pump wave absorption. In particular, the spatial variation of the nonlinear absorption and coupling constants that appear in the coupled-amplitude equations for the probe and the signal (i.e., conjugate) waves are determined. These coupled-amplitude equations are solved numerically in a noniterative manner, leading to a prediction for the phase-conjugate reflectivity. The nature of the predictions differs qualitatively from those1,2 derived from theories that ignore pumpwave absorption, especially for the case of off-line-center excitation. At large values of the input pump intensities, the phase conjugate reflectivity can be larger than that predicted by theories that ignore pump-wave absorption.
Time-resolved studies of molecular atomization by UV-multiphoton laser photolysis
Authors: Colson S. D. , Chen Peter , Biernacki D. T. , Chupka William A. , Berson Jerome A.
Published: February 2023

Pulsed laser excitation in the near ultraviolet is found to be an effective method for the production of free radicals and atoms. Processes requiring numerous photons can be driven with high efficiency, producing large yields of atomic and small polyatomic fragments. The results are similar to those seen for the multiphoton fragmentation of molecular ions formed by multiphoton ionization processes. In this work, multiphoton ionization coupled with MS and PES detection is used to study the neutral products formed from both small and large polyatomic precursors.
Chromatographic effluent detection with laser ionization mass spectrometry
Authors: Opsal Richard , Owens Kevin , Reilly James P.
Published: February 2023

It has been well established during the past decade that atoms and molecules can be efficiently ionized by illuminating them with intense pulses of laser radiation and that spectroscopic information about neutral molecules1 and ions2 can be extracted. One of the major achievements of analytical science, the detection of single atoms, has been achieved by exploiting laser ionization.3 Equivalent sensitivity toward molecules is certainly attainable in principle. However practical systems for detecting molecules must overcome problems associated with background ionization and excited-state molecule dynamics. To increase the detection selectivity made possible by the laser ionization process, sample molecules are introduced into our system through a gas or supercritical fluid chromatograph; the ions generated are mass resolved by a time-of-flight mass spectrometer.4 Recent improvements in our chromatographic systems, mass spectrometer resolution, and GC-MS interface are discussed, along with the application of these to the detection of minute quantities of various priority pollutants.