bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum-confined Franz-Keldysh Effect in CdTe Quantum Dots in Glass
Authors: Esch V. , Khitrova G. , Gibbs H. M. , Jiajin Xu , Liu L. C. , Risbud S. H.
Published: February 2023

Microcrystallites of CdTe were grown in a special-formula glass, yielding the first reported CdTe dots (ro ≅ 36Å). As many as six quantum-confinement peaks1 have been seen in the linear absorption spectrum. These quantum dots are especially suited for electric-field effects because of CdTe′s large Bohr radius (aB ≅ 73 Å). The quantum-dots glass sample was arranged in a waveguide configuration with the electric field applied transverse to the light propagation direction. The samples were 200 to 250 µm thick, and measurements were taken at 8 K. Single photon counting enabled measurement of differential signals as small as 10−5. The observed changes in the absorption spectrum are interpreted to arise mainly from a red shift of the lowest transition and the redistribution of the oscillator strength as forbidden transitions are opened up by the symmetry-breaking action of the external field. This interpretation is made plausible by a strong-confinement Franz-Keldysh calculation similar to that of Miller, Chemla, and Schmitt-Rink2 which predicts a differential absorption spectrum in good qualitative agreement with the data. We also report the first nonlinear optical measurements on CdTe quantum dots, observing the differential absorption during 2-µs pump pulses.
Measurement of Two-photon Absorption by Cr-phthalocyanine in a polycarbonate Film
Authors: Jiang J.P. , Cao X.F. , Hellwarth R.W. , Yu L.P. , Dalton L.
Published: February 2023

We have made what we believe to be the first observation of two-photon absorption in Cr-phthalocyanine. The wavelenth dependence is consistent with the two-photon excitations to Bg energy levels calculated by Ho et al.(1)The strength of acoustic grating formed by intersecting 30 ps pulses in 2microns thick polycarbonate film doped with 3×10−4 mol per gram of polymer Cr-phthalocyanine was monitored by Bragg scattering of a delayed pulse from acoustic pattern. The scattered signal intensity varied as the square of intensities of intersecting 1.06 micron pulses in the range of 0.5 to 2.4 GW/cm2 . The scattered signal was unobservable and at least lowered by factor of 10−2 at the other wavelength studied: 0.532, and 0.59-0.62 micron. This is consistent with the existence of two-photon excitable levels estimated to be near 20,000 cm−1 by Ho, et al.(1) No two-photon transition would be expected at the other wavelengths we used based on energy levels estimated by them.
2 Kilobit Parallel Access Optical Chip for Memory, Logic or Switching
Authors: Chirovsky L. M. F. , D’Asaro L. A. , Kopf R. F. , Kuo J. M. , Lentine A. L. , McCormick F. B. , Novotny R. A. , Boyd G. D.
Published: February 2023

The high interconnectivity of free space optics offers the possibility of powerful new architectures for massively parallel processing and routing of digital information. We have fabricated chips containing the optical devices necessary for the implementation of many such experimental system architectures. The chips are arrays of 32 by 64 unit cells, where each cell is a reflective-mode Symmetric Self Electro-optic Effect Device (S-SEED). The S-SEED is effectively a cascadable three terminal device with all optical inputs and outputs. References [1] and [2] give detailed descriptions of the functionality of the S-SEED as a memory cell, a differential logic gate or a switching latch. Each array requires only two electrical contacts, one for a bias voltage and one for ground. Each unit cell needs two <=5 μm diameter (at a 20 μm spacing) clocked beams (for a total of 4096 per array) with an intensity uniformity within ~±15% at a wavelength within 1nm of the exciton peak wavelength (~850 nm). These are modulated to yield differential output beams with contrast ratios up to 5:1. Each S-SEED can accept two sets of differential input beams. A cell occuppies an area of 20 μm × 40 μm and the entire array size is ~1.3 mm × 1.3 mm. The optical switching energy per cell is between ~1 pJ and ~2.5 pJ, increasing as the bias voltage is increased (6V to 15V) for greater contrast (from 3:1 to 5:1). Sub-nanosecond switching times have been measured for individual devices. For data storage, ~200 nW of optical power per half-cell (or ~1 mW per array) can hold the state of a device indefinitely. This talk will include a discussion of the device and array structures and of the performance data. These chips can make possible optical computing and photonic switching experiments, heretofore existing only in the conceptual stage.
Antireflective "Moth Eye" Structure for Use at Visible Wavelengths: Fabrication and Test Results
Authors: Cox J. Allen , Burbank Dan , Finn Chris
Published: February 2023

Previous experimental (1) and theoretical (2) work has shown that onedimensional gratings having high spatial frequency and simple surface relief profile can produce extraordinary antireflective properties (very low reflectivity over a broad waveband). Such structures are said to show the "moth eye" effect. In previous work, actual devices were made by using laser interferometry in photoresist to define the surface regions for subsequent etching. We have taken a binary optics approach to fabricate a doubly periodic, two-dimensional array of square pits that acts as an effective antireflective structure over the visible spectrum. We used direct-write electron-beam lithography to generate the two-dimensional pattern of squares in high-contrast photoresist deposited directly on fused quartz substrates. The squares were nominally 250 nm on a side and spaced at 350 nm intervals in both x and y directions. After development, the exposed square regions were etched to a depth of 110 nm by reactive ion etching. A SEM photo of the structure is shown in the figure. Areas as large as 1 cur have been fabricated for testing. According to the theoretical model of Gaylord and Moharam (2), our structure should have zero reflectivity at 540 nm and less than 0.5 percent reflectivity at 480 nm and 620 nm. Although our samples show some scatter in the blue, we present measured reflectivity data which agree well with the predicted values. We have also fabricated test devices containing controlled variations in pit depth or width, and measurements of these are presented with comparisons to theoretical values.
Fabrication of large area, solid Fabry-Perot etalons with high finesse
Authors: Gilliand Y. A. , Muller K-H. , Leistner A. , Sainty W. , Seckold J.
Published: February 2023

Large area, solid Fabry-Perot etalons have been manufactured of Z-cut lithium niobate, extending the initial work of Burton et al.1 The finished substrates measure 75 mm in diameter, 210 µm in thickness, and their required thickness uniformity and surface finish is achieved by a Teflon polishing technique. A purpose built phase shifting digital interferometer (PSDI) is used during the fabrication process to monitor the optical thickness uniformity. The finesse and contrast ratio of such solid etalons are measured by precision angle tuning as a function of central aperture. Finesses of 25 and 28 have been achieved for full apertures of 60 and 25 mm, respectively, with a free spectral range of 4 Å.
Detection of atomic hydrogen at low density by two-photon spectroscopy
Authors: Verkerk P. , Grynberg G.
Published: February 2023

We have observed the 1S—3S and 1S—3D Doppler-free two-photon transitions in atomic hydrogen using a powerful narrow-band tunable light source at 205 nm. The excitation is monitored by looking at the fluorescent light emitted on the Balmer α transition. By this method we have been able to detect atomic hydrogen and atomic deuterium at low density (around 107-108 at/cm3). One of the possible applications of this method is the search of superheavy hydrogen atoms. These atoms composed of a heavy proton and an electron are predicted by some supersymmetry theories.1 Because of their important mass shift, they should be easily distinguishable from hydrogen, deuterium, or tritium. Using a preliminary centrifugation, we believe that we can improve the present limit (~10−15) on the abundance of these superheavy atoms.
Fluorescence spectrum of ultracold optical molasses
Authors: Watts R. N. , Lett P. D. , Phillips W. D. , Rolston S. L. , Tanner C. E. , Westbrook C. I.
Published: February 2023

Early experiments on ultracold optical molasses relied on time-of-flight and other ballistic techniques to measure the temperature of atoms released from the molasses.1,2 At the extremely low temperatures observed, the size of the molasses, the effects of gravity, the probe that detected the falling atoms, and the way in which the laser beams forming the molasses were turned off produced a large systematic uncertainty in the temperature determination. Here, we report a direct measurement of the Doppler width of the fluorescence spectrum of Na atoms still viscously confined in the molasses. We determined this spectrum using an optical heterodyne technique and we believe this to be the first time an atomic fluorescence spectrum has been heterodyned. The temperature deduced from the Doppler width is in good agreement with that determined using improved time-of-flight techniques. The heterodyne technique has the added advantage of providing spatially resolved temperature measurements. In addition to the nominally 600-kHz wide Doppler peak, we see a much narrower (60-kHz wide) peak which we tentatively ascribe to Dicke narrowing due to confinement by optical forces.
Demonstration of the quantum Zeno effect with laser-cooled ions
Authors: Itano Wayne M. , Heinzen D. J. , Bollinger J. J. , Wineland D. J.
Published: February 2023

Laser-cooled ions stored in Penning traps are essentially free from collisions and other perturbations that could cause relaxations. This, and the fact that their energy levels can easily be manipulated with rf and laser radiation, makes them well suited for demonstrating certain aspects of quantum measurement theory. The quantum Zeno effect is the inhibition of transitions between states by frequent measurements.1 We have observed this effect in a 9Be+ ground-state rf transition. The measurements are short pulses of light. If the ion is in one state, it scatters a few photons; if it is in the other, it scatters no photons. In the latter case the wavefunction collapse is due to a null measurement.2 The dynamics of this system are similar to those which are predicted to lead to nonexponential spontaneous decay at short times.
Coupling of orthogonal polarizations in a nonlinear, birefringent cavity
Authors: Ho K. C. , Indebetouw G.
Published: February 2023

Polarization bistability has been proposed as having a number of advantages over conventional schemes.1 We have investigated polarization switching in a Fabry-Perot cavity filled with an aligned nematic. In this nonlinear, birefringent cavity, the transmittance for each polarization is a single valued function of the irradiance inside the cavity. This couples the two polarizations so that, unless sufficiently separated spatially, they switch simultaneously. Although limiting the range of possible applications, this coupling may be used to advantage to implement some optical latches.
Optical scanning holography
Authors: Poon Ting-Chung
Published: February 2023

The making of a hologram with long wavelengths can be achieved with a scanning technique (such as in scanned acoustical holography). A local oscillator can supply an electronic reference to a multiplier and low pass filter to extract the phase information of the scattered signal obtained by a scanning receiver.
Polarization effects in anisotropic particle suspensions
Authors: Mcgraw Robert , Rogovin Dan
Published: February 2023

Suspensions of anisotropic particles have demonstrated potential for nonlinear applications in the millimeter1 and optical2 wavelength regimes. In the millimeter regime, strong nonlinear effects may be obtained at very low power levels (1-10 W/ cm2) using stabilized suspensions of large ellipsoidal particles, which are still much smaller than the wavelength of light.1 At visible wavelengths, and correspondingly smaller particles, the strength of the nonlinear interaction is reduced while the response time of the medium is greatly improved.2 In particular, the reorientation times required to form a grating are much shorter than those required for translation motion over distances comparable to the grating spacing.
Improved dimensional stability of Corning 9600 and Schott Zerodur glass ceramics
Authors: Jacobs S. F. , Bass D.
Published: February 2023

Schott Zerodur and Corning 9600 are newly developed glass ceramics designed for high stability structures such as large mirror substrates. In early production these materials suffered from failure to return to length on thermal cycling, which can result in undesirable length and surface figure changes.1 Recently, these materials have been greatly improved by their manufacturers. We present thermal expansion measurements of three vintages of both materials as they were cycled, at least twice, over the 100-475 K temperature range. Thermal equilibrium was obtained after every 25 K temperature increment. The newest Zerodur, called Zerodur M, is virtually free from hysteresis. However, to make this possible the general shape of its cte vs temperature curve has been greatly changed from that of standard Zerodur. (This leads us to wonder whether its homogeneity has suffered). The 9600 material still exhibits a few ppm of hysteresis, but compared with Zerodur M, 9600 maintains its low expansivity to much lower temperatures (100 K).
Novel beam propagation method taking into account continuous reflections
Authors: Lin Hong Huey , Korpel Adrian
Published: February 2023

The beam propagation method, also known as the split-step or marching algorithm, is well known for its application to the simulation of wave propagation in inhomogeneous or cubically nonlinear (Kerr) media. In essence it treats the propagation medium as a sequence of thin phase filters (self-induced in the nonlinear case) separated by thin regions of homogeneous space.1 Reflections due to gradients of the refractive index in the nominal propagation direction are ignored. One recent variant of the technique,2 used for optical waveguide investigations, takes into account multiple discrete reflections by a global iteration scheme. Our proposed method deals with continuous reflections in a marching algorithm fashion, analogous to the way the actual field gradually builds up in the medium. We will present 1-D and 2-D verifiable simulations of (a) backward Bragg reflection interaction with a continuously [n(z)] variable refractive index and (b) reflection off an oblique interface treated as an inhomogeneous [n(x, z)] medium.
Wave propagation through a medium with static and dynamic birefringence
Authors: Silverman M. P. , Badoz J. , Canit J. C.
Published: February 2023

Photoelastic modulation (PEM) makes possible (with phase-sensitive detection) high precision measurement of small polarization changes in light that has interacted with matter. In an ideal modulator an oscillating birefringence (piezoelectrically induced in a silica crystal) leads to phase variations of the form cos(a1), sin(a1), where a1 = A sin(2πft); f is the oscillation frequency and A is the maximum retardation. This standard model cannot account for the results of recent PEM-based experiments to measure optical activity by means of light reflection.1 A more accurate theory, supported by experiment, is given that predicts phase variations of the form cos(b), sin(b)/ 2b, where

2
b
=

[

a
1
2

+

a
2
2

+
2

a
1

a
2

 
cos

(

2
g

)

]

1
/
2

; a2 is the retardation produced by a distributed static birefringence with principal axis inclined at angle g to the modulation axis. Theoretical analysis of the light flux for selected experimental configurations of spectroscopic and polarimetric interest leads to signals at f and 2f that differ markedly from the predictions of the standard model and a two-plate theory with discrete static and dynamic birefringence. Experimental procedures are suggested for circumventing the birefringence-related anomalies in PEM-based reflection spectroscopy of chiral materials.
Image deconvolution using a logarithmic/exponential nonlinear joint transform processor
Authors: Javidi Bahram , Ruiz Jack , Ruiz Carol
Published: February 2023

Recently, we described a nonlinear joint transform processor for image deconvolution.1 In this technique, both the smeared image and the smearing function are displayed side by side at the input plane of the optical processor. The Fourier phase appearing in the joint power spectrum is the exact Fourier phase of the original image. In the technique described in Ref. 1, a hard clipping nonlinearity is used to threshold the joint Fourier spectrum to only two values, 1 and –1. The effect of the nonlinearity is to remove the distorted amplitude entirely and to restore the correct phase of the original signal. An amplitude mask averaged over an ensemble of images is used at the Fourier plane to provide the amplitude spectrum. An inverse Fourier transform of the average amplitude spectrum with the recovered correct phase information can yield the original image with considerably reduced distortion.
Incoherent spatial filtering with longitudinal periodicity
Authors: Poon Ting-Chung , Indebetouw Guy
Published: February 2023

Two-pupil systems have been proposed to overcome the limitations in incoherent optical systems1 and operations such as bandpass filtering have been realized. In this presentation we explore the possibility of realizing bandpass filtering with longitudinal periodicity in a two-pupil interaction system.2 By filtering with longitudinal periodicity we mean that spatial filtering in the transverse directions (x, y) is repeated approximately along the longitudinal direction (z) at a periodic distance. This can be achieved by employing Fresnel zone plates in the pupil planes.
Interactions between first- and second-order couplings to surface plasma waves
Authors: Zaidi Saleem H. , Yousaf M. , Brueck S. R. J.
Published: February 2023

Surface plasma wave (SPW) dispersion relation in the minigap region, where the unperturbed modes are degenerate, has been recently investigated, both theoretically1 and experimentally.2 Theoretically only energy gaps were predicted in the minigap region, but experimentally it was shown that both momentum and energy gaps exist2 although optical excitation resulted only in energy gaps similar to the results obtained by Chen et al.
3
Here we present a detailed optical investigation of the (+1, −2) minigap region by varying grating depths and profiles. Momentum gaps observed were critically dependent on grating profiles.
First-order coupling to surface plasma waves
Authors: Zaidi Saleem H. , Yousaf M. , Brueck S. R. J.
Published: February 2023

Using prism and grating coupling techniques, surface plasma wave effects have been used to investigate metal interfaces, metal-dielectric interfaces, and other nonlinear processes.1 Here we present a comprehensive experimental and theoretical study of first-order coupling to SPWs and the use of this technique to characterize the optical constants of metal films.
Quantum correlations of quadrature amplitudes in nondegenerate parametric downconversion
Authors: Pereira Silvania F. , Peng K.-C. , Kimble H. J.
Published: February 2023

For measurements describable by a discrete set of possibilities, numerous demonstrations of the violation of Bell's inequalities have been reported in optical physics based on observations of polarization correlations for photon pairs. By contrast for observables with a continuous spectrum, there appears to be no general inequalities corresponding to those of Bell and no experimental realization of the original Einstein-Podolsky-Rosen paradox. Following Reid and Drummond,1 we are attempting to demonstrate the EPR paradox in the context of the measurement of continuous quantum variables with a subthreshold optical parametric oscillator operated in a frequency degenerate but polarization nondegenerate mode. In this case, the EPR paradox is formulated in terms of two sets of quadrature phase amplitudes for the spatially separated signal and idler fields. As the parametric gain is increased toward threshold, the quadrature amplitudes of the signal and idler beams become increasingly faithful quantum copies of one another. Our measurements of quadrature amplitudes are carried out using independent balanced homodyne detectors at two sites. When operated for the detection of squeezing at one site, noise reductions of 4 dB relative to the vacuum state limit are observed, which is most encouraging since noise reductions >3 dB in the difference photocurrent from the two sites are sufficient for inference at a distance of a signal observable from a measurement of the corresponding idler variable.
Photon noise reduction by optoelectronic correction using a nondegenerate optical parametric oscillator
Authors: Fabre C. , Mertz J. , Giacobino E. , Heidmann A. , Reynaud S.
Published: February 2023

It has been recently shown theoretically1 and experimentally2 that nondegenerate optical parametric oscillators generate above threshold intense and highly correlated twin beams. More precisely, the noise on the difference between the intensities of the two beams is well below the shot noise for noise frequencies inside the cavity bandwidth. An application of this quantum correlation is to measure the intensity of one beam and use this information to correct the fluctuations of the other beam by optoelectronic means (photodiode, amplifier, and electrooptic modulator). The correction may be applied either on the pumping beam (feedback correction) or directly on the twin beam itself (feed-forward correction).
Homodyne photon-number statistics for nonclassical states of light at a lossless beam splitter
Authors: Campos Richard A. , Teich Malvin C. , Saleh B. E. A.
Published: February 2023

Using the quantum theory of a lossless beam splitter, we determine the joint and marginal photon-number distributions at its output ports, for two arbitrary (not necessarily independent) input fields. The joint probability at the output of the beam splitter turns out to be a Fourier series in the relative phase between the output beams. Photomixing with the number states exhibits no phase sensitivity. An elementary example of phase sensitive dependence in the photon-number domain is obtained with the Bernoulli states, which are a subclass of the binomial states.1 For a joint input Bernoulli state, the probability of detecting one photon (or zero photons) at either output port varies sinusoidally with the relative phase. For independent Bernoulli states incident on the beam splitter, the results differ and depend on whether the input is in a pure or mixed state. Photomixing of other nonclassical states exhibit higher orders of phase-induced modulation of the output photon-number probabilities.
Polarization-resolved optical phase conjugation in liquid suspensions of anisotropic microparticles
Authors: Pizzoferrato R. , De Spirito M. , Zammit U. , Marinelli M. , Scudieri F. , Martellucci S.
Published: February 2023

During the last decade, much attention has been paid to nonlinear optics in liquid suspensions of dielectric, spherically shaped microparticles.1 Such media exhibit very large values of nonresonant third-order susceptibility (χ(3) ~ 101(-7) esu) through radiation-induced diffusive rear-rangement of the particle number density. We report on phase conjugation by degenerate four-wave mixing in liquid suspensions of ellipsoidal polymer microparticles. In these materials, both electrostrictive forces and orienting torques act on the particles, because of the anisotropy of particle polarizability. Thus, in addition to translational gratings, orientational gratings are created, with the particles aligned along preferred directions.2 From the macroscopic point of view, this results in a completely tensorial nature of the χ(3), whereas isotropic particle suspensions show only scalar nonlinearities. We have demonstrated this characteristic by carrying out four-wave mixing measurements with various combinations of the incoming beam polarizations. The predicted polarization states of the outcoming conjugated beam have been observed and the relative conjugation efficiencies reasonably agree with theory.2
Coated nanoparticle composites for intrinsic optical bistability
Authors: Birnboim Meyer H. , Haus J. W. , Kalyaniwalla N. , Ma Weiping , Inguva R.
Published: February 2023

We show that the threshold for intrinsic optical bistability can be greatly reduced by using structured nanoparticles that consist of a nonlinear dielectric core with a metallic coating. Previous calculations based on metallic particles relied on the nonlinear response of the metal particles.1 It has previously been shown that structured nanoparticles2 can obtain a much larger nonlinearity and figure of merit than the metal alone. The calculations we present are based on the greater flexibility allowed by using structured nanoparticles to (i) obtain a local field enhancement in the dielectric core which can consist of a polymer or semiconductor material with a large non-linearity, (ii) obtain the surface plasmon resonance effect and local field enhancement effect by the metallic shell, and (iii) a reduction of the effective metallic loss contribution as the shell thickness is reduced. As in previous studies, ellipsoidal particle shapes can be used to further optimize the local field enhancement.1 We report here results with a PDA polymer as a Kerr nonlinear medium in the core. The metallic shell consists of silver, gold, or aluminum, optimized for various frequency regions of interest. The switching threshold intensity can be reduced below 100 kW/cm2.
MDB: additivity, transitivity, proportionality demonstrated physiologically
Authors: Kaiser P. K. , Lee B. B. , Martin P. R. , Valberg A.
Published: February 2023

In the minimally distinct border (MDB) method two fields are precisely juxtaposed and the observer adjusts their relative radiances until the border between them appears minimally distinct. Fraunhofer was the first to use MDB as a method of visual photometry.1 In 1968, Boynton and Kaiser reintroduced MDB as a photometric technique and showed additivity of luminances.2 Lee et al3 recently demonstrated that the neurophysiological substrate of MDB was evident in the phasic, spectrally nonopponent, M-pathway ganglion cells. They moved a heterochromatic border across the receptive field of monkey (M. fascicularis) retinal ganglion cells and measured the spike rate as a function of the luminance ratio across the border of the bipartite field. They determined that the spectral sensitivity of m-pathway cells closely matched the human 10°V(X) function. As a photometric method, MDB obeys the rules of transitivity, additivity, and proportionality. We demonstrate these properties in the nonopponent, m-pathway ganglion cells of the macaque monkey.
Raman scattering study of AuGe ohmic contact to GaAs
Authors: Yee J. C. , Fauchet P. M.
Published: February 2023

According to the commonly accepted theory,1 AuGe forms an ohmic contact with n-type GaAs by having Au combining with Ga to form various AuGa compounds, thereby leaving Ga vacancies in GaAs. Ge then occupies these Ga vacancies and as a result dopes heavily the underlying GaAs region. The width of the surface depletion region caused by the characteristic surface Fermi level pinning is thus reduced, and electrons are therefore able to tunnel through this barrier resulting in a linear I-V relationship. In this experiment, thin AuGe and Au contacts are made to Si doped n+GaAs. Polarized Raman spectra are taken in the backscattering geometry to determine the possible changes in doping level under the contacts. We find that both samples show an increase in doping directly underneath the contacts. By analyzing the ratios of LO and L− lines, the doping concentration is estimated to have increased from ~2.3 × 1018 to 5 × 1018 cm-3, which is however not enough to produce efficient tunneling and ohmic behavior.1,2 Since this increase is also present in the contact without Ge, it is presumably caused by the excess Si in the n+GaAs occupying the Au- induced vacancies. This experiment suggests that the function of Ge in AuGe contact is more subtle than previously thought, and the commonly accepted theory needs to be modified.
Laser-induced degradation of GaAs
Authors: Campbell I. H. , Fauchet P. M.
Published: February 2023

Laser-induced degradation of GaAs bandgap photoluminescence (PL) has been reported by several workers1,2 but the physical mechanism responsible for this decrease remains unclear. The degradation is not caused by surface oxidation and it is thought to be the result of a nonradiative recombination enhanced defect reaction.1 Using in situ Raman scattering (RS) and PL we have observed significant decreases in bandgap PL and the formation of solid arsenic at the sample surface. In addition, the lattice temperature and the electron temperature of the spot being damaged have been measured by RS and PL, respectively. We present results as a function of laser power, dopant type, and density and for both capped and free GaAs surfaces.
High spectral resolution lidar measurement of vertical backscatter ratio profile of atmospheric aerosols
Authors: Alvarez Raul J. , Li Y. H. , She C. Y.
Published: February 2023

Although a basic lidar system performs the expected function of light detection and ranging very well, it cannot measure atmospheric parameters directly unless the backscattered light from air molecules (Rayleigh scattering) and that from aerosol particles (Mie scattering) can be separated spectroscopically. Recently, we proposed a new high spectral resolution lidar (HSRL) technique for measuring the profiles of backscatter ratio and atmospheric temperature based on Rayleigh/Mie scattering and the use of a proposed narrowband atomic blocking filter.1
Possibility of phase problem solution via a programmable optical signal processor
Authors: Dmitriev N. I. , Burkov V. I. , Lokshin G. R.
Published: February 2023

We have considered an original and a simple phase retrieval method using a programmable optical signal processor. The simplest processor allowing one to measure the phase ϕ(x, y) consists of a controlled spatial light modulator (CSLM), lens, photodetector, ADC, and computer. The spatial modulator (for example, liquid crystal modulator) is set immediately in front of the lens. In its focal plane there is a point photodetector which, by means of an ADC, is connected with the computer intended for handling the information obtained and controlling the CSLM. Complex field E(x, y) = |e(x, y)| expiϕ(x, y) belongs to the function class represented by the Fourier series where {
mn
(y)} is the orthogonal basis. If the CSLM is programmed for generation transmission according to {ψ
mn
(x, y)}, {ψ
pq
(x, y) + ψ
mn
(x, y)}
m
≠
p, n
≠
q
and {iψ
pq
(x, y) + ψ
mn
(x, y)}
m
≠
p, n
≠
q
[where ψpq(x, y) is a reference function], then, via the point photodetector, exhaustive information about complex array {c
mn
} can be obtained. In this case the phase retrieval is performed by the computer.
Laser diagnostic density measurements of Hg(3P0,1,2) in a Hg-Ar discharge
Authors: Bigio Laurence
Published: February 2023

Two laser-based techniques are used to measure absolute and radial density distributions for the 6(3p0,1,2) states of mercury in the positive column of a low pressure Hg-Ar dc discharge. In the first method, a pulsed dye laser beam (20 ns, 0.2-cm–1 bandwidth), traversing the discharge axially, is scanned through one of the 6(3 p 0,1,2)→ 7(3S1) transitions, depending on the lower state of interest. The transmitted signal is detected with a calibrated photodiode and the power loss on resonance is plotted as a function of nonresonant power. At sufficiently high powers, this power loss approaches a constant saturated value which is directly proportional to the initial number density of absorbers in the lower state. Relative density measurements are made by setting the power in the saturated regime and measuring this power loss as a function of radial position. Results are given for the three 3P states at Hg pressures of 1 and 7 mTorr and discharge currents of 80 and 400 mA. Absolute densities are established using a well-known interferometric technique known as the hook method.1 Using the same laser as described above, the dye laser is tuned through the 3P1→3S1 transition of interest, and the spectral separation of the interference hooks is used to determine the absolute density.
Degree of polarization of polychromatic light transmitted through a birefringent plate
Authors: Foley John T.
Published: February 2023

When a linearly polarized, polychromatic plane wave of light is normally incident on a birefringent plate whose faces are principal planes, the transmitted light is in general partially polarized. For this problem the degree of polarization of the transmitted light has been investigated for incident beams with specific spectral profiles.1,2
Origins of liquid crystal birefringence dispersion
Authors: Wu Shin-Tson , Wu Chiung-Sheng
Published: February 2023

Liquid crystal spatial light modulators (LC SLMs)1 have important uses in optical processing, such as wavelength conversion, wavefront correction, and optical computing. LCs with high birefringence and low viscosity are highly desirable for enhancing the figure of merit of the LS SLM. In this paper, a three-band model which consists of one σ → σ
*
and two major π → π
*
electronic transitions was developed to account for the birefringence dispersion of a uniaxial liquid crystal. By comparing theory with experimental results, the contribution of each band to the overall birefringence is evaluated quantitatively. The effect of each band on birefringence dispersion depends strongly on the conjugation length of the LC molecule. By increasing the conjugation length along the principal molecular axis, the longest π → π
*
transition plays an ever-increasingly important role in birefringence, whereas the contributions from the σ → σ
*
and the first π → π
*
transitions decrease.
Coherent optical link demonstrations for space communication
Authors: Shaik Kamran , Chen Chien , Win Moe , Marshall W. K. , Ansari Homayoon , Rayman Marc
Published: February 2023

Development of a coherent optical communication system using frequency stabilized solid state lasers for eventual deployment in space is being actively pursued at the Jet Propulsion Laboratory. A demonstration system transmitting at 1.06 μm with low to moderate data rates has been implemented. Both the transmitter and the local oscillator (LO) employ frequency stabilized (Δv ~ 5 kHz), diode pumped Nd:YAG monolithic ring lasers. Frequency tuning and phase locking are accomplished piezoelectrically with a response time <1 μs.1 Pulse position modulation of the transmitted beam is accomplished by an external GaAs acoustooptic modulator. At the receiver, the signal is mixed with the LO, detected, and processed to retrieve the data stream as well as the error signal for frequency tuning and phase locking of the LO laser. At low data rates, the small received signal energy (per laser coherence time) makes receiver phase and frequency tracking the limiting factor in system performance.
High accuracy fiber sensor using optical bistability
Authors: Li Chun-Fei , Zhang Lei , Wu Jie , Liu Lijun
Published: February 2023

Conventional optical fiber interferometric sensors are based on optical fringe counting. The precision depends on the interval between two fringes, namely, half-wavelength. Here we propose a novel optical fiber sensor using a two-beam interference hybrid optical bistable device; an electrooptical crystal modulator is set in one beam, and a fiber for measurement of the temperature is set in another beam. These two beams are combined and interfered as output light. Part of the output light is received by a detector and converted into an electric signal to control the modulator.
Characterization of darkening in semiconductor doped glasses
Authors: Malhotra J. , Hagan D. J. , Potter B. G.
Published: February 2023

CdS
x
Se1-
x
semiconductor doped glasses are known to darken on intense laser irradiation, the darkening being accompanied by a decrease in the nonlinear refraction coefficient and faster recombination times.1 We have performed experiments to characterize this darkening in a number of commercial CdS
x
Se1-
x
glasses. A transmission spectrum (540-820 nm) of the darkened sample indicates that darkening is of a broadband nature. Measurements were made as a function of fluence, repetition rate, and pulse width using a picosecond, frequency doubled Nd:YAG laser. A cw He-Ne laser probe operating at 633 nm was used to monitor the change in transmission during sample irradiation. Darkening was found to increase rapidly during initial stages of laser irradiation and then level off, after which no further change was observed. Darkening was measured at a pulse width of 20 ps for fluences ranging from 4 to 50 mJ/cm2. The final extent of darkening is greater for larger fluences, the maximum change in transmission measured being ≃6%. For a given fluence, stronger darkening was produced at a pulse width of 64 ps than at 20 ps while darkening at 64 and 140 ps was approximately the same. This rules out simple excited state or two-photon absorption mechanisms.
Standing-wave SAW modulator for optical communication
Authors: Kissa Karl , Hunsperger R. G. , Ih Charles S. , Wang X.
Published: February 2023

Progress has been made on an integrated acoustooptic modulator needed for a proposed optical communication network. The system, which is described elsewhere,1 can employ a standing wave surface acoustic wave (SWSAW) to generate microwave subcarriers needed to multiplex analog and/or digital signals. Previous experiments demonstrated intensity modulation of a guided optical beam at a frequency of 70 MHz by a SWSAW which diffracted light in the Raman-Nath regime.1,2 Intensity modulation of an optical beam at 600 MHz has been observed recently using a Bragg version of this modulator. Superimposing NTSC VHF TV signals on the bias current of the laser diode resulted in mixing between the TV signals and the 600-MHz acoustooptic modulation. Hence, the VHF TV signals were optically upconverted into the UHF range by the acoustooptic modulator. A photodiode was used to convert the UHF signals back into an electrical form. The carrier-to-noise ratio (CNR) was at least 30 dB for the picture carriers of the upconverted TV signals. The observed picture quality was good.
Low power, high speed optical phase conjugation using chiral smectic optically addressed spatial light modulators
Authors: Mao C. C. , Johnson Kristina M. , Arnett K. , Handschy M. A. , Moddel G.
Published: February 2023

Optical phase conjugation has many uses, including image transmission through fibers, coherent image amplification, aberration correction, pointing and tracking, and high resolution microscopy. However, its practical application has been limited by the fact that no available phase conjugating material combines fast response with high sensitivity. Using an optically addressed spatial light modulator (OASLM), which is composed of an amorphous silicon photosensor and a ferroelectric liquid crystal modulator,1 we achieved optical phase conjugation at low optical power (5 mW/cm2) and a response time (30 µs) 3 orders of magnitude faster than similar experiments reported using a nematic liquid crystal OASLM.2,3 The diffraction efficiency of our device is ~1%.
Transverse discharge system for high repetition rate metal vapor lasers
Authors: Kim J. J. , Sung N. , Lee S.
Published: February 2023

Pumping self-terminating metal vapor lasers require, among other things, a fast rise time of the electrical power that is deposited in the lasing medium at high temperatures, e.g., above 1500°C for the copper vapor laser. The best way to obtain a fast rise time is to transversely couple a low inductance electrical pulse forming circuit with a high temperature laser cell. One of the major problems involved in designing such a system is caused by the high temperature that has to be dealt with. We describe a transverse electrical discharge system that pumps high temperature metal vapor lasers with a rise rate of current in excess of 104 A/ns at a repetition rate of several kilohertz. This system was used to pump a new version of the transverse discharge copper vapor laser (TDCVL)1 at 5 kHz in a steady state mode, generating an unoptimized average laser of 1.8 W. The laser power was a linear function of the repetition rate. It is demonstrated that self-heated TDCVLs can be developed for practical applications.
Analytical modeling of a XeF(C→A) excimer laser
Authors: Hofmann T. , Dane C. B. , Hirst G. J. , Wilson W. L. , Sauerbrey R. , Tittel F. K.
Published: February 2023

A model has been developed to describe the injection control of a pulsed laser amplifier using an unstable resonator.1 The coupled rate equations for the gain, absorption, and photon flux are numerically integrated allowing the correct treatment of the saturation of both gain and absorption. An extension of this model is reported in which the spatial overlap of the multiple amplifier passes is incorporated into the calculation to more accurately describe the laser saturation processes. In addition, externally located mirrors are modeled by the treatment of the unpumped regions in the cavity and the inclusion of laser cell window losses. This model is used to predict the performance of an electron-beam pumped XeF(C→A) excimer laser over a wide range of experimental configuration using both external and internal optical resonators. The input data for the small signal gain and absorption are derived from experimental net gain and fluorescence measurements and are found to be consistent with the predictions of kinetic calculations. Good agreement is achieved between model predictions and experimental measurements of laser output energy and temporal profile.
Numerical analysis of the lateral modes of gain-guided GaAlAs diode lasers with a concave facet
Authors: Champagne Yves , Mccarthy Nathalie
Published: February 2023

Enhanced lateral mode stability and reduced output beam divergence in the plane of the active layer have been recently observed with narrow stripe gain1 and index guided2 diode lasers with a cylindrically concave etched facet. A major consequence of this geometry is the focusing of the intracavity beam after reflection on the facet. In narrow stripe lasers, this improves the matching of the fundamental lateral mode with the narrow lateral gain profile. The radius of curvature of the facet has a major influence on lateral mode characteristics. A careful analysis is therefore required to estimate the best design parameters prior to fabrication. We used the beam propagation method since it is well suited as a numerical tool for the investigation of these nonsymmetric resonators with waveguiding geometries. We found that the beam divergence may be significantly reduced, and this reduction is generally accompanied by a lower oscillation threshold. Although the calculated lateral mode distributions are different from those obtained with conventional gain guided lasers, the excellent lateral mode discrimination proper to these devices seems to be preserved with the concave facet.
Optical model of the angular dependence of monochromatic soft x-ray interaction with layered structures
Authors: Sher C. J. , Krol A. , Kao Y. H.
Published: February 2023

Monochromatic soft x-rays can be utilized as a nondestructive probe of microscopic structure in heterojunctions by measurement of the angular dependence of their reflectivity, total electron yield (TEY), and fluorescence yield (FY). Interference between the x-rays incident and reflected from the buried interface creates modulation in the radiant energy distribution, which results in the characteristic oscillation pattern in the angular profile of the scattered radiation. The angular dependence of TEY and FY maps the integrated electromagnetic field depth distribution weighted by the soft x-ray photon attenuation length (for FY) or the secondary electron mean free path (for TEY) in the investigated material. The interaction of the soft x-rays with the stratified media is described by the optical electromagnetic wave solution to the Fresnel equations on each interface.1 Heterojunctions grown by molecular beam epitaxy were investigated by means of reflectivity and TEY at the U15 beamline of the National Synchrotron Light Source at Brookhaven National Laboratory. By fitting the experimental data to the model, the layer thickness, surface and interfacial rms roughness parameter, and refractive index were obtained. This demonstrates the use of the optical model of x-ray interaction with heterojunctions, and the value of reflectivity and total electron yield as a tool for the study of layered systems.
All optical switch using elliptically birefringent single-mode fiber
Authors: Chen C. J. , Wai P. K. A. , Menyuk Curtis R.
Published: February 2023

We study the performance of a fiber all-optical switch. The switch configuration is in the form of a Mach-Zehnder interferometer similar to that proposed by Lattes et al.
1
The operation of the switch is based on both the nonlinear and birefringent properties of the fiber.
Diffractive multiorder beam dividers
Authors: Shin D. , Magnusson Robert , Moharam M. G.
Published: February 2023

Low spatial frequency gratings (i.e., Raman-Nath diffraction regime) exhibit multiple diffracted waves excited by a single incident plane wave. The energy distribution among the diffracted waves depends on the magnitude of the modulation and on the grating shape. For some applications, it is of interest to produce structures which support multiple diffracted waves with approximately equal intensities. Periodic arrays of dielectric cylinders were reported to have this property.1 In this paper, surface relief structures with conic (elliptic, hyperbolic, and parabolic) cross-sectional grating shapes are studied as an extension of this work. Better uniformity in the intensity distribution among the orders compared with dielectric cylinders is possible. In particular, a variable number of fairly evenintensity diffracted orders with reasonably sharp cutoff is found to be obtainable. Integral expressions, based on simple transmittance theory, are given for the complex amplitudes of the diffracted waves. These expressions are evaluated using an exact rigorous coupled wave theory2 and experiments. Potential applications include elements in multiple imaging, optical interconnection of networks and devices in integrated optics and communication systems, machine vision, as well as general beam division.
Spectroscopic studies of samarium monoxide
Authors: Bujin Guo , Linton C.
Published: February 2023

Using a high resolution, selectively detected cw eye laser excitation technique, we have successfully investigated twenty prominent electronic transitions of samarium monoxide. Ten lower lying electronic states [X0− υ = 0, 1, (1)1, (2)0+, (1)2, (2)1, (1)3, (3)0−, (2)2, (3)2, (1)4] have been rotationally excited to six upper electronic states. The samarium monoxide was formed using a Broida-type oven or sputtering source.1 The excitation spectra were taken by carefully setting the monochromator to detect the transitions while scanning a Coherent Autoscan ring dye laser. By using the parity selective properties of Ω = 1—0 transitions,2 we were able to separate the e and f parity components in the [16.9]1—(1)1 and (1)2 transitions. Most of the lower lying energy levels have been related by more than two transitions. The assignment of the rotational lines was mostly made by first lines from the band origin. The combination difference was used to confirm the assignment and helps to proceed with the assignment. The same perturbations observed in two different transitions also help to assign the spectra. For most of the transitions, the two most abundant samarium isotopes (154 and 152) have been assigned and fitted by a least-squares fitting program. The other four more abundant isotopes (150, 149, 148, 147) have also been analyzed for a few transitions and the isotope effect for the rotational B values have been compared.