bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunable spatial filter: a two-pupil processing technique
Authors: Poon Ting-Chung , Park Jinwoo
Published: February 2023

Defocused optical transfer function of a scanning acoustooptic heterodyning two-pupil system has recently been reported.1 In this paper, we explore its potential application in tunable incoherent spatial filtering. For example, with two offset pupil functions both having Gaussian shape we can achieve tunable bandpass filtering operations. The passband of the filter can be chosen by varying the size of the pupils, and the center frequency can be tuned by changing the separation of the offset pupils as well as the amount of defocus.
Femtosecond hybridly mode-locked cw dye lasers at yellow and deep red wavelengths
Authors: Dawson Martin D. , Garvey Dennis W. , Boggess Thomas F. , Smirl Arthur L.
Published: February 2023

Direct generation of optical pulses with duration below 100 fs from cw dye lasers has almost exclusively been limited to the 605–630-nm spectral range. Typically, the use of conventional ring or antiresonant ring cavity arrangements designed to utilize the colliding pulse mode-locking (CPM) effect,1 where counterpropagating pulses meet in a saturable absorber jet stream, is also required. We describe the generation of near transformlimited pulses as short as 55 fs at 675 nm and 69 fs at 583 nm from a linear cavity, synchronously pumped, hybrid cw dye laser which does not require the CPM technique. The laser was pumped at 82 MHz by 650-mW average power, 70-ps pulses from a mode-locked and frequency-doubled cw Nd:YAG laser. The dual-jet resonator was terminated by a two Brewster prism and plane mirror arrangement used to introduce variable intracavity dispersion. Optimal laser performance was achieved by iterative adjustments of the intracavity dispersion and cavity length. Femtosecond pulse generation was obtained using the gain/absorber dye combinations of sulphorhodamine 101/DQTCI and rhodamine 6G/DQOCI and DODCI mix. Average output powers were 35 mW at 675 nm and 55 mW at 583 nm, respectively, for these combinations.
Periodicity in orientation discrimination threshold
Authors: Price P. , Regan D.
Published: February 2023

We measured orientation discrimination threshold at 7.5° increments around the clock for an 8-cycle/deg grating subtending 1.0° that was located 1.25° from the foveal center. Threshold was lowest for vertical and horizontal gratings. However, rather than rising monotonically to maxima for oblique orientations, threshold rose sharply to submaxima for gratings inclined at only ~20° to hori­zontal or vertical before falling to weak subminima at oblique orientations. This finding held for both subjects tested. It is consistent with the idea that orientation discrimination is determined by the reltive activity of two or more orientation-tuned neural elements,1 and that the retinal area tested addressed only 4-8 such elements. This idea can also explain how subjects unconfound orientation change from covarying stimulus parameters even though cortical neurons are generally sensitive to several stimulus parameters.
Squeezed states: an overview
Authors: Yurke Bernard
Published: February 2023

A squeezed state of the electromagnetic field has less noise in one of its two amplitude components than that of a coherent state. This property makes squeezed states potentially useful in low noise and precision measurement. Squeezed states may be generated by, among other things, degenerate parametric amplifiers and four-wave mixers. The reduced noise in one of the amplitude components is most easily observed via a homodyne detector. A number of experimental efforts to generate and detect squeezed states are under way. Here, in describing experimental techniques, the experiments' carried out by Slusher et al. are emphasized. A number of techniques were employed to successfully generate squeezed light. An atomic beam of sodium provided the optical nonlinearity in a cavity-backward four-wave mixer. By employing pairs of Fabry-Perot modes spaced symmetrically about the pump frequency, squeezed light was generated in nondegenerate conditions where Rayleigh scattering of pump light could be avoided. To observe squeezing, a number of nonidealities such as phase jitter and detector inefficiencies also had to be overcome.
Nonclassical photon statistics in the transmission from a resonant cavity containing a single atom
Authors: Rice P. R. , Carmichael H. J.
Published: February 2023

We consider an optical cavity containing a single two-level atom driven on resonance by an external laser source.1 We focus on the limit of weak excitation where the dynamic response of this system is governed by just three parameters: the atom-field coupling constant g, spontaneous emission rate γ for the atom, and cavity decay rate κ. The statistics of the transmitted light are analyzed as a function of g, γ, and κ, in terms of the second-order correlation function g(2)(τ), and the quadrature variances measured in a homodyne detection scheme. Squeezing and photon antibunching exist over a wide range of parameters. For γ ~ κ, the system can exhibit an oscillatory response, even when the mean intracavity photon number is much less than unity.2 The oscillations can be understood in terms of the coupling between the free atom-field eigenstates |0,−>, |0,+>, and |1,−>. The oscillation frequency is determined by the energy level splitting produced between the degenerate one-quantum states |0,+> and |1,−> by the atom-field interaction. The second-order correlation function can exhibit a novel nonclassical effect, where, for g(2)(0) ≠ 0, at some finite delay τ0, the correlation function dips exactly to zero—g(2)(τ0) = 0.
Strained-layer superlattice detectors and detector concepts
Authors: Osbourn G. C.
Published: February 2023

Strained-layer superlattices (SLSs) made of alternating layers of InAsSb have recently been proposed as alternative III–V materials for infrared detector applications in the 8–12-μm wavelength range.1 The wavelength cutoffs of certain SLS structures in this material system are theoretically predicted to be extendable to 12 μm through the effects of the elastic layer strains in the InAs-rich layers. These III–V materials are expected to be more stable than the HgTe-rich HgCdTe alloys due to the greater bond strengths of the III–V materials. However, the use of superlattices as photovoltaic detector materials introduces new considerations for the design of high efficiency devices. In particular, superlattices typically exhibit minority carrier diffusion lengths along the growth direction which are less than one-tenth of the in-plane diffusion lengths.2 This paper reviews the issues involved in tailoring the wavelength cutoff of infrared superlattice materials and designing efficient photovoltaic detector structures using these materials.
Nonlinear propagation in birefringent optical fibers
Authors: Menyuk Curtis R.
Published: February 2023

Single-mode fibers are really bimodal due to the presence of birefringence. The amplitudes of the two modes u and v satisfy the equations where δ = πcΔn/D(λ)λ0 is the birefringence strength and R = 8πct0/λ. Other parameters are defined as in Ref 1. If we assume a pulse whose FWHM width is 5 ps, we find that 0.3 < δ < 3.0 for typical fibers. The smallest value of δ in actual fibers is 1.4 × 10−3, while R = 1.4 × 10−4. We then find that Rδ ≫ 1 in all cases, so that the exponential terms are rapidly oscillatory and can be dropped. As a consequence, there is always an effect due to the birefringence. Solitons which mix the two polarizations are a factor of 6–5 more intense than those which consist of a single polarization. Linearly, the two polarizations will split over 20 km when δ > 0.1, while nonlinearly the two polarizations are bound together even when δ = 1 if the normalized pulse amplitude is large enough to generate a soliton.
Chromatic adaptation, the control of chromatic adaptation, and color constancy
Authors: Maloney Laurence T. , Varner Denise C.
Published: February 2023

Recent work in computational color vision1,2 demonstrates that it is possible to achieve exact color constancy using only the kinds of information available to biological vision systems. These algorithms first compute an estimate of the illuminant in the scene and then transform the initial color signal so as to eliminate the contribution of the illuminant. We examine this work and relate it to research in color vision through the following linking hypothesis: local retinal state is chosen to compensate for the illuminant. With this linking assumption, we demonstrate that the computational work speaks directly to current and past models of adaptation in visual color psychophysics. Further, the work emphasizes the distinction first clearly drawn by Stiles between the local adaptation state of the retina and the (global) control of adaptation and suggests a broad class of experiments addressing these issues.
Squeezing in nondegenerate two-photon two-level media
Authors: Capron Barbara A. , Holm David A. , Sargent Murray
Published: February 2023

We recently1 calculated the amount of squeezing predicted by our quantum theory of multiwave mixing for a one-photon two-level model. Here we use the corresponding theory for the two-photon two-level model,2 which allows for nonsaturating nondegenerate pump and probe waves and includes dynamic Stark shifts. We simplify the more complicated general model using a fourthorder perturbation limit and find very simple expressions that show even for very weak pumps with no Stark shifts or atomic detuning significant squeezing can be achieved. Much of this squeezing is due to scattering of the conjugate field off the pump-induced two-photon coherence, which does not arise in the one-photon case. In general, Stark shifts induce large regions of significant gain, resulting in instabilities. We also show results for high intensity pumps that require larger atomic detunings to obtain a large amount of squeezing. The low intensities required in the two-photon case should make squeezing easier to observe than in the one-photon case.
Theory of squeezed light generation in optical fibers
Authors: Milburn G. J. , Reid M. D. , Walls D. F. , Shelby R. , Levenson M. D.
Published: February 2023

We give a quantum theoretical analysis of squeezed light generation via nondegenerate four-wave mixing in an optical fiber. The medium is modeled by an ensemble of anharmonic oscillators and loss is included. We include the coupling to acoustic phonons which gives rise to guided acoustic wave Brillouin scattering (GAWBS). The GAWBS introduces random noise which destroys the squeezing at room temperatures. By cooling the fiber to temperatures ~2 K the GAWBS is substantially reduced and the observation of squeezing becomes possible. A comparison is made with the recent experimental results of Levenson et al.1,
2
A scheme to suppress the GAWBS at room temperatures using a two-frequency pump and difference detection is analyzed and the conditions in which good squeezing results are determined.
Theory of squeezing in low Q cavity
Authors: Lane A. , Reid M. D. , Walls D. F.
Published: February 2023

A theory calculating the squeezing generated via intracavity four-wave mixing in a two-level atomic medium is presented. Previous theories have assumed a high Q cavity such that the atomic linewidth γ⊥ is much greater than the cavity linewidth κ and one can adiabatically eliminate atomic variables. We do not make this assumption.
High-speed GalnAsSb/GaSb PIN photodetectors for wavelengths to 2.3 μm
Authors: Zyskind J. L. , Bowers J. E. , Srivastava A. K. , Burrus C. A. , DeWinter J. C. , Pollack M. A.
Published: February 2023

Photodetectors are needed for future communications systems utilizing novel mid-infrared fiber materials with extremely low predicted losses in the 2–4-μm wavelength range. We report improved performance of front-illuminated Galn-AsSb/GaSb PIN homojunction photodiodes1 that operate with high speed and high quantum efficiency at room temperature. The photodiodes consist of a Zn-diffused homojunction 0.3 μm below the surface of a 3-μm thick layer of rt-type Ga0.82ln-0.18As0.17Sb0.83. This layer was grown by liquid-phase epitaxy on a GaSb substrate and doped with Sn to a level of n = 2.5 × 1015 cm-3. A partial metallization of the 100-μm diam mesa surface allows for front illumination of the chips, which are packaged as described in Ref. 2. The external quantum efficiency without antireflection coating is constant at 55–65 % for wavelengths up to 2.2 μm. At 1.06 μm the impulse response of the detector has a FWHM of 110 ps. At 1.3 μm it responds to pseudorandom modulation at bit rates up to 4 Gbit/s.
Observation of a cone radiation in sodium vapor
Authors: Han Xiaofeng , Lu Zhenguo , Ma Zuguang
Published: February 2023

We report the first observation of a cone radiation at 5890–5896 Å (ωL) in sodium vapor pumped by an excimer laser–dye laser tunable over a 334–347-nm (ωP) range. Simultaneously, with the cone radiation two tunable stimulated emissions were detected: the 3S–4S (Ω) stimulated electronic Raman scattering transition at 2.38–2.65 μm (ωS), and the 4S–3P transition at 1.138–1.142 μm (ωT). On the hollow ring of the upward cone radiation three spectral lines appear at 5890, 5896, and 5894 Å. The first two wavelengths are fixed and the third is slightly tunable during the tuning of the dye laser. The cone size varies with the sodium vapor pressure and it disappears, while the buffer argon pressure is higher than 20 Torr.
Quantum fluctuations, phase wave, pump depletion, and diffraction dynamics in three-level superfluorescence
Authors: Mattar F. P. , Friedman E.
Published: February 2023

Delay statistics of amplified quantum initiation of SF are reported as manifestly important in both the pump/SF partial and total overlap regimes for τp/τR < 1 (pump pulse length to cooperative radiation time ratio) as a function of the Fresnel number F for a given atomic density N. The Mattar et al. formulation1 is adopted with phase, transverse variations, and copropagation in conjunction with the Bowden and Sung2 initiation through Langevin forces of bivariate normally distributed amplitudes and uniformly random phase in both pump and SF transitions lp and lsf. Unusual temporal distortion is exhibited in the SF pulse for some trajectories when lp is present, F is large, and τp is shortened. However, when diffraction strengthens, i.e., decreases, the communication between adjacent shells improves and significantly reduces the statistics uncertainty associated with the delay difference σ (τdp – τdsf)/[τdp + τdsf], and the less likely the phase wave is to be exhibited. The SF is not shielded from any fluctuations in the pump pulse.
Vibrational relaxation of adsorbed molecules
Authors: Cavanagh R. R. , Casassa M. P. , Heilweil E. J. , Stephenson J. C.
Published: February 2023

Time-resolved measurements of vibrational relaxation rates have determined the population decay of vibrationally excited OH groups: adsorbed on high surface area SiO2; in model silanols; and as defect sites in quartz.1 Depopulation of the vibrationally excited OH oscillator was found to occur on a time scale of 80-300 ps. The temperature dependence of the vibrational relaxation rates in quartz (OH) and on SiO2 (OH and OD) were all found to follow a simple multiphonon relaxation model.2 However, the relative rates for the two isotopes (rateOD/rateOH = 1.6) on SiO2 did not scale as predicted by the theoretical models (rateOD/rateOH = 13). Recent measurements of isotopicaliy substituted silanols (R3SiOH and R3SiOD dilute in CCI4) also find OD decay times comparable with those of OH. The observed decay rates appear to be dominated by processes which proceed through a SiOH bending mode. Prospects for extending these methods to longer wavelength with improved temporal resolution are discussed.
Surface microroughness measurement for a laser mirror
Authors: Chen Yi-Sheng , Wang Wen-Gui
Published: February 2023

In high energy lasers and many other applications, the scattering from a laser mirror is a limiting factor in the performance. Significant improvements in mirror and window components have been achieved by increasing the understanding of scattering mechanisms and coating technology.
Acoustooptic processor for real-time synthetic aperture radar Image formation
Authors: Stalker K. T. , Molley P. A. , Sandoval M. B. , Humphreys S. L.
Published: February 2023

A real-time optical processor has been built to investigate the applicability of optical processing to synthetic aperture radar image formation. By taking advantage of the high processing speed and large time-bandwidth product of acoustooptic devices (AODs) combined with the multichannel correlation capability of CCD detectors used in the time delay and integrate (TDI) mode, a small real-time SAR processor can be built. The required 2-D matched filtering operation is first performed in range using the AOD and then the azimuthal matched filtering is performed using either a fixed or alterable mask in a TDI correlator configuration.1 A processor has been built to investigate the effect of system architecture on image quality and system complexity. The system is described and experimentally obtained PSF and image data are shown. The potential for system miniaturization and ruggedization is also discussed.
Alzheimer’s disease: a disorder of the precortical visual system?
Authors: Cronin-Golomb Alice , Corkin S. , Growdon J. H.
Published: February 2023

Alzheimer’s disease (AD) is characterized by maximal degeneration of the parietal and temporal lobes with relative sparing of primary visual areas. As may be expected from this pattern of degeneration, AD patients as a group are widely impaired on tests of higher-order visuospatial function, whereas only a minority show deficiencies in color vision, Vernier acuity, and stereoacuity. This pattern of functional sparing of basic visual processes does not hold, however, for contrast sensitivity function, which is commonly impaired at all spatial frequencies in patients with AD, relative to age-matched controls.1 In cats, ablation of the striate cortex results in only modest changes in contrast sensitivity function; furthermore, blocking the ON channel in the monkey retina affects contrast sensitivity but not color discrimination, acuity, motion detection or stereopsis. Thus contrast sensitivity, unlike the other basic visual functions we have measured in AD, may involve precortical brain areas. In light of a recent report of optic nerve degeneration and retinal changes in AD,2 these observations raise the intriguing possibility that, as far as basic visual processes are concerned, AD is a precortical, not a cortical disease.
Possible chemically pumped alkali metal diffuse band lasers
Authors: Kleiber Paul D. , Stwalley William C. , Gole James L.
Published: February 2023

Recent studies1,2indicate that the Na2violet diffuse bands are an attractive candidate for a short-wavelength chemically pumped laser. These excimer transitions have now been analyzed and unambiguously assigned using single-mode laser excitation; they arise from the superimposition of two distinct continuum (bound-free) emission bands—one singlet

(

2
1

Σ
u
+

−

X
1

Σ
g
+

)

and one triplet (primarily

2
3

Π
g

−

1
3

Σ
u
+

).1In beam experiments, the reaction Na3+ X → (NA2)* + NaX(where X= Cl, Br, I) yields direct and efficient chemiluminescence, including emission in the singlet violet band, with sharp bimodal excited state vibrational distributions; the fluorescence resembles that characterizing optically pumped alkali dimer lasers.2In sodium heat pipe ovens, the violet bands have been efficiently produced using various pumping techniques. The selectivity probably arises from the near-resonant dissociative recombination process

Na

3
+

+

e
−

→

Na

2
*

(

2
1

Σ
u
+

 
or
 

2
3

Π
g

)

+
Na

. Substantial gain and minimal absorption have been measured in the violet in high density Na vapor pumped by a cw krypton laser. Similar possibilities exist for other alkali metals.
Visible chemical laser potential of the Mg(3P)/Sm system
Authors: Stanfill J. D. , Chang R. S. F. , Djeu N.
Published: February 2023

Previous studies have shown the N2O/CO/Mg reaction to be capable of efficiently producing Mg(3P) in large concentrations.1,2 On the basis of the favorable energy level positions of Sm, we have embarked on a study of the feasibility of a visible chemical laser through transfer of energy from Mg(3P) to Sm. Fluorescence measurements from flowing mixtures of Mg and Sm vapors under both pulsed and cw laser excitations on the Mg(1S—3P) transition have been made. Intense emissions from a number of Sm transitions in the green region were observed. Preliminary time-resolved fluorescence decay data taken over a range of Sm densities yielded a quenching rate for Mg(3P) approximately ten times the gas kinetic rate. Relative steady-state fluorescence intensity measurements showed that nearly all the collisions result in the excitation of Sm. These findings indicate that an efficient visible chemical laser based on the Mg(3P)/Sm system may be possible if a suitable gas for deactivating the chosen lower laser level can be identified.
Demonstration of a simple optical finite state machine and restoring all-optical digital logic
Authors: Smith S. Desmond
Published: February 2023

We reported the first digital all-optical circuits using steady-state continuous-mode optically bistable devices which can be optically biased and held close to switchpoint and which give an incremental change of output sufficient to switch succeeding elements.1,2 These circuits have been demonstrated using cascadable elements constructed, respectively, from InSb (using electronic nonlinearities) and ZnSe refractive interferometric devices. This approach derives from the original (1979) observations of steady-state optical bistability3 and gain in an optical transphasor.4 Cascadability, fan-out, and fan-in are essential elements of an all-optical digital parallel computer in which, in the first instance, the opportunity provided for massive parallelism through the simplicity of optical interconnects is seen as one of the prime routes to be investigated toward realizing very high logic rates. With the requirement for restoring logic that there be gain in addition to regions of valid logic-0 and valid logic-1, we show that for digital optics this can be readily achieved by the technique of hold-and-switch. The use of off-axis address for the holding (or optical bias) and signal beams allows digital circuits to be constructed with the required features of restoring logic which can be infinitely extensible given sufficient supply of separately holding beams which can be construed as the power supplies of ensuing circuit elements.5
Low-switching energy optical bistable devices
Authors: Dagenais Mario , Sharfin W. F.
Published: February 2023

We describe two approaches to low-energy switching and optical bistability. In one approach, which is a more fundamental approach, we use the nonlinearity associated with bound excitons in CdS to demonstrate the lowest total switching energy (4 pJ) of any optical device exhibiting two stable output states for the same input intensity.1 Bound excitons were chosen because they are known to have a very large oscillator strength (f = 7), a fast radiative decay (tspont = 500 ps), and they do not diffuse in the crystal, thus permitting a sharp focusing geometry. Furthermore, they are a good approximation to quantum dots. In a different experiment we have operated a standard diode laser structure below threshold and have demonstrated an efficient optical switch that can be used in thresholding and decision-making applications. The device switches with <400 aJ (4 × 10−16 J or <3000 photons) of optical energy incident on the device.2 During the switching operation, only 10 pJ of electrical power is dissipated. The switch operates at room temperature, is compatible with optical communication systems, and has a gain of the order of 15 dB, leading to the important properties of cascadability and large fan-out. The operation of a high contrast (5:1) AND gate was demonstrated.
Aging and human cone photopigments
Authors: Burns Stephen A. , Elsner Ann E. , Berk Lawrence , Rosenberg Paul
Published: February 2023

Previous studies1,2 have disagreed about the effects of aging on human cone optical densities. We have examined the question of whether there are age-related changes in the density and half-bleach illuminance of normal observers. We used a color-matching method to measure the optical density of the photopigments within cones. Forty normal observers between the ages of 12 and 69 were tested. The subjects made color matches for 4° fields at nine retinal illuminances from 260 to 260,000 td. All patients older than 50 had an additional eye exam to insure normal retinas and optic media. The measured optical density changes minimally with age (0.001/yr). The illuminance that bleaches half of the cone photopigment does not show any monotonic change with age. The average half-bleach illuminance is 4.36 log td (s.d. = 0.139); the average optical density for a 4° field is 0.27 (s.d. = 0.07). The current measurements are insensitive to changes in the relative numbers of cones and to moderate changes in the clarity of the optic media. Age-related changes in these measures of photoreceptor function are minimal, although disease-related changes can be large.
Hole contributions to the photorefractive effect in n-type Bi12SiO20
Authors: Strohkendl F. P. , Hellwarth R. W.
Published: February 2023

Electrons have until now been considered as the only charge carriers involved in the photorefractive effect on Bi12SiO20. We observed that the excitation rate of holes in such a crystal is actually about one-third of that for electrons. We use the recently published theory for hole-electron competition in photorefractive materials1,2 to determine the average distance traveled by both carriers between excitation and recombination, their respective optical absorption coefficients, and the density of photorefractive sites. This set of parameters is obtained from beam-coupling gain measurements and time constants of light-induced grating erasures.
Radiative transitions in calcium ions
Authors: Baluja K. L. , Taylor K. T.
Published: February 2023

Oscillator strengths in both length and velocity approximations have been obtained for transitions between the fifteen lowest lying states of Ca III with dominant configurations 3p6, 3p54s, 3p54p, and 3p53d calculated using the program of Hibbert.1 These states (all corresponding closely to a pure LS coupling scheme) were each represented by about twenty single electron configurations that allowed for internal, semi-internal, and all-external correlations by means of single and double electron excitations to pseudoorbitals

5
¯

s
,

5
¯

p
,

4
¯

d
,

4
¯

f

. Of these correlations the most important was found to be that linking 3p2 to 3d2 arrangements, a fact not previously recognized for this ion. The excitation energies calculated for these states agree satisfactorily with the previous experimental results of Borgstrom.2 By using these calculated states of Ca III as those of the residual ion in a close-coupling calculation, oscillator strengths between various discrete states of Ca II have been calculated together with the photoionization cross section from the ground state of this ion.
Evaluation of the Klntz solid-state anomaloscope
Authors: Geri George A. , Neri David F.
Published: February 2023

Kintz1 has recently described an inexpensive and portable anomaloscope whose test and primary stimuli are derived from LED bicolor light bars (Hewlett-Packard). We have assessed the validity (against a standard Nagel anomaloscope) and test–retest reliability of this instrument in classifying 36 color-defective observers. In addition, we have obtained normative data on 54 normal trichromats. Of the 14 deuteranopic and 8 deuteranomalous observers tested, 19 (86.4%) were classified identically on the Nagel and Kintz anomaloscopes and 21 (95.5%) were classified identically on the test and retest using the Kintz anomaloscope. Of the 9 protanopic and 5 protanomalous observers tested, 11 (78.6%) were classified identically on both instruments and all observers were classified identically on the test and retest using the Kintz anomaloscope. Although the Kintz anomaloscope appears to be a valid and reliable device for classifying color-defective observers, several design modifications are suggested for further separating the primaries in chromaticity space, for balancing the luminosity of the primaries, and for facilitating calibration of the instrument.
Wavelength-dependent chromatic Broca-Sulzer effect
Authors: Osaka Naoyuki
Published: February 2023

The brightness of a chromatic flash is a joint function of its luminance and chromaticity.1 The concomitant change in brightness and hue response with changes in luminance and chromaticity suggests a marked interaction between chromatic and achromatic coding systems. Bowen and Nissen1 did not find the wavelength-dependent Broca-Sulzer effect under hue substitution using nonunique hues, in which a flash represents chromaticity modulation without luminance modulation. However, the present data showed the chromatic Broca-Sulzer effect under both hue substitution (test and background with 5 cd/m2) and increments (background with 0.5 and 1.6 cd/m2) paradigms using unique hues as stimuli. The unique hues (blue, green, and yellow) were measured beforehand and they are the loci of equilibrium points for opponent coding systems. The methods employed were scaling and signal detection procedures. The results showed a wavelength-dependent Broca-Sulzer effect.
Azide reactions for advanced chemical lasers
Authors: Coombe Robert D.
Published: February 2023

An efficient short-wavelength chemical laser will be a device which couples a highly constrained chemical pumping mechanism with an atomic or molecular species whose spectroscopic characteristics are appropriate for lasing. Research in the past several years has identified a number of candidates (e.g., interhalogens, group VI atoms and molecules, CN, NO, and others) which are capable of lasing in the UV or visible regions. Recent work in our laboratory has sought means by which the very highly constrained reactions of azide radicals may be used to pump these known candidate systems. The electronic ground state of N3 correlates adiabatically to an excited N(2D) atom and a ground state N2 molecule. As a consequence, R + N3 reactions effectively proceed on excited state potential energy surfaces and are very strongly constrained to produce electronically excited metastable NR molecules. This view is supported by experimental studies of reactions of N3 with a number of first and second row atoms.1,2 The products of these reactions are useful as either energy storage agents or lasing species in a number of potential SWCL systems. N3 reactions can be operated in either continuous or pulsed modes. Pulsed experiments with these systems hold promise for early tests at reagent densities commensurate with measurable gain levels.
Color normalization algorithm based on material categories
Authors: Rubin John M. , Richards Whitman
Published: February 2023

Let image intensity be measured through each of three spectral filters S, M, and L. Let each image region be mapped to a point in a color space R. If the illuminant is white, points in different quadrants of R will correspond to distinct materials.1 Suppose that given a random collection of materials, half reflect more light in the S sample than in the M, and independently, half reflect more in the L than in the M. (Any fixed percentages will do.) Then an image under white light of a random set of materials will, when mapped into R, yield approximately the same number of points in each quadrant. If an image of random materials maps into R so that quadrants are unevenly populated, it can be inferred that the illuminant is not white. Normalization coefficients s and I can then be found so that the quadrants of the new space are equally populated. One crucial problem is that many natural images (e.g., forest scenes) do not contain a random collection of materials. The spectral crosspoint operator2 can specify a subset of image regions more likely to represent a random set of materials than the set of all image regions (which might contain repeated materials). Normalization can then proceed with this subset.
Properties of generalized minimal mapping theories for apparent motion
Authors: Grzywacz Norberto M.
Published: February 2023

The minimal mapping theory, a computational theory for apparent motion,1 postulates that the motion correspondence process matches features in consecutive viewing frames so as to minimize their total distance traveled. We explored some computational properties of this theory. For rotating objects we found that the correct matching percentage of minimal mapping algorithms decreases with angular displacement. An alternative theory, the structural theory, postulates that the matching is such that it minimizes 2-D structural changes of the object. The performance of structural algorithms is independent of the angular displacement, being poorer than that of the minimal mapping theory for small angles, but better at high angles. The best of both worlds may be obtained by a hybrid theory of the above two. We also explored the inclusion of motion inertia2 into the minimal mapping theory. This was done by an increase, through a simple cosinusoidal law, of the effective distance between features in consecutive frames whose putative motion is in a direction different from that of the past motion. This modification accounts for the extant psychophysical data on ambiguous motion.2 Surprisingly, the predictions of this inertial minimal mapping theory include noncrossing in transversal collision experiments and better performances under rotation.
Parallel motion detection
Authors: Bulthoff Heinrich H. , Little James J.
Published: February 2023

We have devised simple, local motion detection schemes providing information which can be integrated with other vision modalities to segment images. A simple scheme proposed for motion detection in the rabbit retina,1 based on a logical comparison between image elements separated in time and space, can detect locally the direction of motion but not its velocity. To avoid aliasing (in time and space), the input is filtered by the Laplacian of a Gaussian and then thresholded at zero. The simple rabbit scheme is enhanced to suppress false motion detection at isolated intensity changes (e.g., changes in illumination and receptor noise). To compute velocity, this scheme has been extended to multiple scales, where each scale is selected by changing the size of the Gaussian mask. Also, the criteria have been narrowed to detect motion only at the selected scale. The fly motion detector (Reichardt-Correlator)2 uses image grey values, multiplying neighboring receptor signals, after asymmetric temporal filtering. The rabbit implementation uses simple local binary operations to compute motion, permitting easy parallelization. On the Connection Machine, a mesh-connected parallel computer with nonlocal communication, motion detection on natural images can be performed in real time.
Photofragmentation dynamics of molecular oxygen
Authors: Hill W. T. , Keller J. W. , Ederer D. L.
Published: February 2023

The polarization of fluorescence from excited photofragments contains valuable information on the decomposition dynamics following excitation and fragmentation. Specifically, it is possible to determine the anisotropy (alignment and orientation of population within the fragments) characterizing the fragmentation (ionization and/or dissociation) processes.1 We have measured the polarization of

O
2
+

fluorescence as a function of input photon energy to determine the alignment in the

b
4

Σ
g
−

and A2∏
u
states. Monochromatized synchrotron radiation, from the NBS-Gaithersburg Synchrotron Radiation Facility (SURF II), was employed to photoionize an effusive beam of O2 into the A and b states of

O
2
+

while the polarization of the subsequent A → X and b → a fluorescence was monitored. The results of our measurements are presented and contrasted with recent photoelectron angular distribution measurements2 on O2 in the same energy region.
A 1-GHz GaAs acoustooptic modulator device
Authors: Soos J. I. , Rosemeier R. G.
Published: February 2023

The experimental performance of a GaAs Bragg cell was accurately predicted utilizing a LiNbO3 transducer bonded to a GaAs substrate. The major parameter for the selection of GaAs as a substrate was its high acoustooptic figure of merit.1
Aberration calculation and lens tolerancing using automatic differentiation
Authors: Herloski Robert
Published: February 2023

Automatic differentiation is a technique that allows one to easily calculate exact partial derivatives of complex, composite mathematical functions. This technique is described in a book by Rall1 of the University of Wisconsin at Madison. Independently, S. Marshall of Xerox Corp. developed an algorithm that is effectively automatic differentiation, and extends the technique to arbitrary order partial derivatives of functions of arbitrary number of independent variables. Since aberration coefficients are merely partial derivatives of final ray coordinates with respect to initial ray coordinates, automatic differentiation can be employed to calculate any aberration coefficient desired of any lens system, including misaligned and nonsymmetric ones. Partial derivatives of these systems for use in lens tolerancing and optimization can also be directly calculated. Examples of aberration calculation and Gaussian beam tolerancing, using an implementation of ray tracing and automatic differentiation in the ADA programming language, are given. The work of Forbes2 in the area of computation of chromatic aberration coefficients using an equivalent, highly optimized power series method, is also mentioned.
Intracavity far-infrared laser spectroscopy of ions and Van der Waals molecules
Authors: Saykally Richard J.
Published: February 2023

Far-infrared laser magnetic resonance is used to measure rotational spectra of simple cations generated in intracavity discharges.1,2 Hyperfine energy levels are resolved, revealing the electron spin density distribution in the molecules. A similar technique, employing an intracavity supersonic free jet and an electric field for tuning, is used to measure vibration-rotation spectra of Van der Waals bonds. The bend and stretch motions of the Van der Waals bonds3 in ArHCl and KrHCl have been studied with hyperfine resolution. A detailed description of the potential energy surface is obtained from analysis of these spectra.
Radiator reorientation kernels by tunable energy compensation
Authors: Thomas J. E. , Liang J. M. , Dasari R. R.
Published: February 2023

We describe a new Stark sublevel photon echo technique for measuring fluctuations in macroscopic coherences. This idea is applied to the Stark tunable infrared (λ = 9 μm) R(4, 3, V3 = 0 → 1) transition of 13CH3F to measure, for the first time, the radiator reorientation velocity changing kernels WΔ
M
(Δv) which describe the rates (per unit velocity) at which the radiator orientation M changes by an amount ΔM accompanied by a velocity change Δv.1 In the experiments, two pulse photon echoes are obtained using a laser field polarized along an applied weak de Stark field (

z
^

direction) which shifts each M transition by Mvs (Hz).
Review of recent x-ray laser experiment results
Authors: Matthews Dennis L.
Published: February 2023

We are vigorously continuing our research into the design, demonstration, and application of the Nova laser-pumped x-ray laser. Using exploding foil1,2 plasma amplifier designs we are pursuing inversion schemes using neon, nickel, and other ionization sequences in an effort to achieve significant single-pass or multipass amplification at wavelengths shorter than 10 nm. We report the status of our measurements of the saturation energies, coherent power, beam divergence, modal purity, and other laser characteristics. We also describe our designs and progress on demonstration of multipass amplifiers. Finally, a review is given of the various interesting applications of x-ray lasers having wavelengths in the 3-10-nm regime.
Atomic physics of neonlike soft x-ray lasers
Authors: Chen M. , Hazi A. , Reed K. , Scofield J. , Whitten B.
Published: February 2023

This paper focuses on three topics: identification of n = 3−3 transitions observed in the emission spectra of Se, Y, and Mo, calculation of electron collision strengths for n = 2−3 transitions, and the effect of dielectronic recombination on the kinetics of neonlike lasers. We have used a semiempirical procedure, based on relativistic, multi-configurational calculations of energy levels and previous experimental data for Z ≤ 26, to identify the n = 3−3 emission lines of Se24+, Y29+, and Mo32+ in XUV spectra obtained in different irradiation conditions. Some magnesium-like and fluorinelike transitions have also been found. Since the primary pumping mechanism for the unexpectedly weak j = 0−1 laser line is electron collisional excitation from the neonlike ground state, we have compared the excitation cross sections calculated with several different distorted wave codes and examined the effects of resonance contributions due to sodiumlike doubly excited states. We have included detailed dielectronic recombination rates, calculated with a multiconfigurational Dirac-Fock method,1 in a simple kinetic model for neonlike lasers and found that this process is an important mechanism for populating the j = 2 upper laser levels when the density of fluorinelike ions is relatively large.2
Collisional broadening of hydrogenic ion transitions of interest in x-ray lasers
Authors: Kelleher Daniel E. , Oza D. , Greene R. L.
Published: February 2023

The gain coefficient depends on the differential oscillator strength at the peak of the lasing transition. Thus it depends directly on the spectral width of the transition. We discuss below the collisional broadening of hydrogenic transitions in plasmas. In a plasma, atomic and ionic transitions are broadened by collisions with electrons and ions. This effect tends to be particularly large for hydrogenic radiators, which experience a first-order Stark effect. In line-broadening, a hydrogenic radiator is one in which a level in the transition is quasi-degenerate with another level to which it is dipole-coupled, i.e., their energy separation is smaller than their homogeneous width. The Balmer-alpha (n = 3 → 2) transition of C5+ has been used by the Princeton x-ray laser group to achieve an enhancement of stimulated-to-spontaneous emission by a factor of ~100.1 We have performed detailed calculations of the collisional broadening of this line and the Balmer-beta (n = 4 → 2) transition over a wide range of plasma conditions. The calculations include dynamic many-body ion collisions, which are the dominant broadening mechanism. For plasma conditions of current x-ray laser experiments,1 the collisional width of Balmer-alpha is comparable with the Doppler width, and at higher densities it dominates.
Supermode structure of diode laser phased-arrays with nonuniform channel spacing
Authors: Kapon Eli
Published: February 2023

Varying the laser spacings in diode laser phased arrays provides a potentially useful degree of freedom in the design of these devices. Variable spacing array structures have been proposed for tailoring the supermode field patterns1 and for achieving supermode discrimination.2,3 In this work, the supermode structure of nonuniform-spacing arrays is discussed. These structures were analyzed both by using coupled-mode theory and by direct solution of Maxwell’s equations. It was found that varying the laser spacings can be used to tailor the supermode field patterns. In particular, the channel spacings can be designed so that the fundamental supermode exhibits virtually uniform channel excitations, which reduces its beam divergence. However, the variable spacing does not improve the supermode discrimination compared with the case of uniform arrays. In a variable spacing array with N channels, supermodes v and N + 1 − v (v = 1,2, …N) have nearly degenerate modal gains. This is different from the strong supermode discrimination exhibited by chirped (variable channel-width) arrays. New array structures which combine variable channelwidth for supermode control and variable spacing for field pattern tailoring are described.
Optical index of gallium arsenide-aluminum arsenide superlattices in the near infrared
Authors: Zavada J. M. , Jenkinson H. A. , Hubler G. K.
Published: February 2023

The synthesis of high quality gallium arsenide–aluminum arsenide (GaAs–AlAs) superlattices has initiated a new class of optical materials with important consequences in the area of optoelectronics. For many applications it will be necessary to accurately characterize the optical properties of these materials in frequency regions of interest. In the present investigation, infrared reflectance spectroscopy is used to determine the optical indices of several GaAs–AlAs superlattice films in the near-infrared region (4000–10,000 cm−1). Each of the superlattices under study had an average aluminum mole fraction equal to 0.523. The reflectivity measurements indicate that the optical index of a particular superlattice can be higher or lower than that of the equivalent AlGaAs alloy depending on the layer periodicity of the superlattice. These results are compared with theoretical treatments of GaAs–AlAs superlattices1 and with prior experimental studies at energies above 1.2 eV.2
Low-temperature thermal expansion of beryllium as an optical material
Authors: Browder James Steve , Ballard Stanley S.
Published: February 2023

A study has been completed on hot isostatic pressed beryllium to determine its suitability for mirrors to be used in space telescopes.1 This study was performed for the Perkin-Elmer Corp, on small cubic specimens cut from specified locations in various shaped large blanks of the material. The coefficients of thermal expansion for the samples were measured along various orthogonal directions to determine their isotropy in the temperature range from 60 to 310 K. Similar measurements were made on samples from various locations to determine their homogeneity. Graphs comparing the expansivity of beryllium against other optical materials2 are presented to illustrate the suitability of this form of beryllium as a mechanical support for optical elements.
Retinal image stabilization facilitates perception of an illusory square wave grating
Authors: Higgins Kent E. , de Monasterio F. M. , Kitterle F. L.
Published: February 2023

Inspection of a spatial triangular luminance profile gives rise to the perception of an illusory square wave grating.1 Since the illusory square wave could be seen in the afterimage of an objective triangle wave, Leguire et al.
1
suggested that the illusion was not due to eye movements. We have investigated the role of eye movements by comparing the illusion in unstabilized viewing conditions and in stabilized retinal image conditions using an SRI double Purkinje-image eyetracker.2 Compared with unstabilized viewing, stabilized viewing facilitated the appearance of the illusion in two ways. First the latency of the illusion (measured from triangle wave onset to the first appearance of the illusory square wave) was reduced. Second, the illusory square wave percept was evident for a greater proportion of viewing time in stabilized rather than in unstabilized viewing conditions. However, while retinal image stabilization tended to stabilize the perception of the illusory square wave, it did not eliminate the apparent contrast reversal of the illusory pattern.