bluuebunny/crossref_metadata_2025 huggingface dataset:
Picosecond infrared spectroscopy using a regenerative amplifier
Authors: Jedju T. M. , Rothberg I. , Roberson M.
Published: February 2023

An apparatus for doing picosecond, narrowband infrared spectroscopy is presented. The procedure, based on a 540 Hz regenerative amplifier, uses a gated up-conversion technique. Spectral resolution of 1 cm−1 is achieved by difference-frequency mixing the output of a narrowband, sync-pumped, grating dye laser, which is pumped by residual light from the regenerative amplifier, with 532 nm laser light in LiI03. The output is narrowband infrared with a relatively high intensity compared to a cw source and is easily tunable over 500 cm−1 around 5 u. Time resolution of ps is achieved by a gated up-conversion technique. We plan to improve our resolution to fs by compressing out the laser light used for gating. The high repetition rate of the regenerative amplifier, in concert with synchronized phase-sensitive detection, provide outstanding signal-to-noise values. Detection of pump-induced transmission changes of the probe pulse of less than one part in a thousand has been demonstrated. This sensitivity is needed to do transient, vibrational spectroscopy where the typical ratio of vibrational cross-sections to electronic cross-sections is about 10−3. We have applied our system to experiments on ligand dissociation of CO from carboxymyoglobin.
Polymer integrated optical polarizer
Authors: Yuen S. , Chrostowski J. , Syrett B.
Published: February 2023

There has been an increasing interest in using organic polymers to implement waveguide devices. Organic polymers have low intrinsic losses, and devices that use these materials are easy and inexpensive to fabricate. This paper reports the first polymer integrated optical polarizer built on silicon that uses an antiresonant, reflecting optical-waveguide (ARROW) structure.1 The integrated device consists of a low-index polymer core on top of two interference cladding layers that are deposited on a silicon substrate. Although ARROW structures have low transmission losses for TE polarized light (dB/cm), losses for TM polarized light are large (60 dB/cm), making them excellent integrated optical polarizers. The prototype polymer-rib ARROW polarizer was designed for operation at 820 nm. The first and second interference cladding layers were made up of 0.16 m of Si3N4 and 2 m of SiO2. A commercially available photosensitive polymer, NA 61, was used as the core. A 4 m polymer layer was spin-coated onto the first cladding layer. Rib structures 10 m wide were defined by means of conventional photolithography in the prototype devices. Extinction ratios greater than 40 dB/cm were measured. The performance can be further improved by optimizing the coupling between the source and the rib waveguides.
Deuterium plasma reduction of the free-carrier level in GaAs for optical waveguides
Authors: Zavada J. M. , Weiss B. L. , Theys B.
Published: February 2023

Exposure of bulk GaAs (either n- or p-type) to a hydrogen or a deuterium plasma can be used to passivate the sample surface, thereby reducing the free-carrier concentration. This in turn will modify both the refractive index and the free-carrier absorption, thereby making the samples suitable for optical waveguides.
Characteristics of hybrid modes in biaxial planar waveguides
Authors: Maldonado Theresa A. , Gaylord Thomas K.
Published: February 2023

Light propagation in biaxially anisotropic dielectric crystals may be conveniently described by the two-sheeted wave vector surface. Each sheet represents the properties of one of the two allowed orthogonally polarized propagating waves. In general, the two allowed propagating waves are "extraordinary-like," and the Poynting (ray) vector direction for each wave differs from the wave vector direction. Dielectric planar waveguides may be biaxial, either naturally or through the electro-optic effect (as is frequently the case with modulators). The electromagnetic fields in a biaxial waveguide consist of a weighted sum of four "extraordinary-like" plane waves which are coupled. The directional properties of the hybrid guided modes are determined by using a complete and concise coordinate-free approach for isolating each sheet of the wave vector surface. The ranges of propagation constants for the hybrid modes are determined as a function of the orientation of the principal dielectric axes, and this leads to the classification scheme that uniquely identifies each guided mode.
Computer simulations of fully cascadable picosecond all-optical logic using nonlinear semiconductor étalons
Authors: Richardson D. , Gibbs H. M. , Koch S. W.
Published: February 2023

Nonlinear Fabry-Perot étalons have been studied vigorously in recent years as potential all-optical decision-making elements. Fundamental physical and engineering tradeoffs have thus far prevented their use in real-world systems. Bistable devices can be cascaded at megahertz rates but require strong holding powers and fail to demonstrate useful gain for subnanosecond pulses. Two-wavelength logic-gate étalons can switch in picoseconds with picojoule energies but have thus far proved difficult to cascade. In this talk we propose a paired semiconductor étalon scheme that attempts to solve these problems, and we present the results of computer simulations of the device concept. In the envisioned architecture a two-wavelength NOR-gate étalon is operated in series with an "upconverter" étalon to allow cascadable operation on a picosecond timescale. The paired device is predicted to achieve a fan-out of at least 2 and good overall contrast, requiring about 75 pj to perform a single logic operation/upconversion. Related simulations indicate that the NOR-gate étalon itself requires a minimum of 28 pJ to achieve the same contrast and fan-out. Thus the price for cascadability is basically a threefold increase in input energy over the NOR-gate alone. The energy requirement might be reduced through the use of multiple-quantum-well materials. The computer simulations of the device behavior are based on a realistic model for the carrier-density-dependent optical nonlinearities of bulk GaAs.
Two-photon excitation spectra of NO Rydberg states O’2II–, H’2II–
Authors: Zhao Shuo-Yan , Zhong Ming-Cheng , Zhang Pei-Lin
Published: February 2023

Two photon excitation spectra of nitric oxide molecule from XII1/2, X2II3/2 to 4d Rydberg state O′2II– (v = O, 1) have been observed by using a frequency-doubled dye laser (283.4-293.5 nm). Ten rotational branches O21 + P11, P21 + Q11, Q21 + R11, R21 + S11, S21; O22 + P12, P22 + Q12, Q22 + R12, R22 + S12 and S22 are assigned for O′2II– – X2II– (0,0) band and (1,0) band. Rotational lines of P21 + Q11 and Q21 + R11 branches are easily observed to J = 24 and J = 16, respectively. Rotational analyses of these branches allow calculation of accurate values of O′2II– state rotational constants and vibronic level energy. For v = 0, Bv = 1.997 ± 0.002 cm–1, To = Te + G(v) = 68944.0 ± 0.8 cm–1 and for v = 1, Bv = 1.985 ± 0.002 cm–1, To = 71283.6 ± 0.8 cm–1. Fifteen branches of the excitation spectra from X2II– to 3d Rydberg states H′2II– (v = 1, 2, 3) in the 287.8–308.4 nm region are studied. Molecular constants of H′2II– state are obtained: for v = 1, To = 66010.1 ± 0.8 cm–1, Bv = 1.968 ± 0.002 cm–1; v = 2, To = 68316.9 ± 0.8 cm–1, Bv = 1.942 ± 0.002 cm–1, and v = 3, To = 70587.1 ± 0.8 cm–1, Bv = 1.941 ±v 0.002 cm–1. Laser-induced spectra of NO from various vibronic levels of H′2II–, O′2II– states are also observed. Emission spectra H′ 2II––D 2Σ+, C 2II, C 2II-A 2Σ+ are in the IR region (800–1150 nm); O′ 2II–-C 2II, D 2Σ+ in the visible region (630–690 nm); and the fluorescence progressions D 2Σ+, C 2II, A 2Σ+–X 2II to v" = 11 in the UV region (170–340 nm).
Dielectric films deposited with the C-MAG™ sputtering process
Authors: Felts John T.
Published: February 2023

The introduction of the C-MAG™ rotary cathode has ushered in a new era for thin film sputter deposition of silicon oxides and nitrides. For the first time, production large area DC sputtering of both oxides and nitrides of silicon is possible. The coating is deposited at rates consistent with existing glass sputtering lines and produces near stoichiometric films. The thin films are amorphous, resistant to abrasion, adhere well to plastics, metals and glass, and provide a barrier to gases. The combination of the silicon oxide and nitride coatings with Airco Coating Technology's existing sputtering processes ushers in a new and exciting time for thin film stack development.
Nonlinear circuit-based simulation of an acousto-optic bistable device
Authors: Chatterjee Monish R. , Huang Jen
Published: February 2023

Detection, amplification, and feedback of the diffracted light (typically first-order) from an acousto-optic cell operating in the Bragg regime, back to the transducer driving the cell results in a bistable device.1 Iterative simulations show that hysteresis in the diffracted electric field can be observed for nominally low values of the feedback parameter solely as a consequence of the delay during the feedback. For higher values of the feedback parameter, the diffracted light field exhibits controlled (chaotic) oscillation. In the work presented in this paper, we developed an effective and accurate nonlinear circuit model that takes into account both the coupling between the fields, as well as the field-dependent positive feedback parameter. Thus, by simply assuming real fields, and replacing the electric field amplitude and the spatial coordinate by voltage and time respectively, a nonlinear circuit equivalent for the system is obtained via nonlinear dependent sources supplying currents to capacitors whose initial voltages are set by the incident field amplitudes. The system is tested for hysteresis and chaos subject to varying sound pressure and feedback gain.
Interaction of planar, multitone-modulated ultrasonic waves on optical beams with arbitrary profiles
Authors: Banerjee Partha P. , Tarn Chen-Wen
Published: February 2023

Most of the electrical signals applied to the transducer of a acousto-optic (AO) device are not simply cw signals. For the purpose of applications, it is necessary to investigate the interaction between optical beams and multi-tone-modulated sound waves. Starting from the coupled wave equations for the optical fields in the AO sound cell, with the sound field as a multitone amplitude-modulated signals, a Fourier-transform technique is used to express the interactions in spatial frequency domain. A number of the coupled differential equations, which describe the interactions between the optical fields and sound fields of each side band, can be obtained. Due to the fact that there is no analytic solution for these coupled equations, a well-known numerical technique, namely, the Runge-Kutta method, is employed to solve the equations. To check the formulation, Bragg diffraction of a Gaussian light beam is considered. Detailed numerical simulations, comprising Fourier transforming the input beams profile to calculate the spectra of the scattered beams, and hence their profiles in space using the inverse transform are presented.
Optical probe of standing wave for visualization of ultrasonic traveling wave front
Authors: Yi Ming , Zhu Li , Yang Xuan-min , Gan Jin-Fu
Published: February 2023

Optical probe for visualizing ultrasonic traveling wave-front has long attracted considerable attention in the acoustics field. In recent years, we have established a series of methods to display the image of wave-front for ultrasonic traveling wave of an acousto-optic device. The methods are based on the correlation theory and by using cw laser beam. Special spatial filtering technique has been used. (It is different from the general spatial filtering technique for the steady phase object, for instance, Schlieren method, Zernike phase contrast method, dark ground field method, etc.) It is based on considering the temporal frequency spectrum in spatial frequency spectrum of ultrasonic traveling wavefront which is a moving phase object illuminated by multi-frequency light beam which is one of the diffracted beams of standing wave device driven synchronously with the traveling wave device through a frequency dividing circuit. By analyzing the temporal frequency spectrum in the spatial frequency spectrum of the traveling wavefront illuminated by one of the diffracted beams which has multi-frequency and different phase, we have taken a special spacial filtering technique to obtain a high contrast image of the ultrasonic traveling wavefront. The results of our experiments are well desired as the theory predicted by us. The technique is more convenient to be established and much cheaper than others.
Measurement of window homogeneity
Authors: Ai Chiayu
Published: February 2023

The inhomogeneity of a window material can be observed by immersing the window into a liquid between two planes, or polishing both surfaces of the window to flats much better than the amount of inhomogeneity. These two methods are inconvenient for most applications. A new method which can measure the inhomogeneity independent of the quality of the optical surfaces of the window will be presented. This technique requires four measurements. First the two surfaces of the window are measured, next the window is measured in transmission followed by a reference flat, and finally the window is removed and a measurement is taken with the reference flat. These measurements are then combined to find the inhomogeneity of the window. The method requires that both surfaces be polished; however, there can be several fringes of deviation from flatness. A small wedge between the two surfaces will eliminate effects due to spurious reflections. One advantage of this technique is the removal of system error due to the interferometer. If the rms error due to random noise (i.e. repeatability) is Δ for a phase measurement, the resulting error in the homogeneity measurement is 1.6Δ for an index of refraction of 2. This pa per will describe this technique in detail and show experimental results.
Optically induced and charge-transport-assisted electroabsorptive and electro-optic nonlinearity in cadmium telluride
Authors: Ziari Mehrdad , Steier William H.
Published: February 2023

We have observed the optically triggered formation of a high electric field region underneath the negative electrode. The optical control of the magnitude and the position of this field build-up, typically 10 to 20 times the applied field, combined with the electro-optic or the Franz-Keldysh effect, provides a novel large optical nonlinearity. The high field region (0.1-0.2 mm wide) forms in few microseconds upon illumination by below bandgap light (860-900 nm) and persist in the dark with a latch time of 2-5 s. This effect is highly sensitive, requiring approximately 10 nJ/cm2 absorbed fluence, and exhibits an intensity and applied voltage dependent response time. Furthermore, this high field can be erased by illuminating the region through ITO electrodes with near bandgap light (835-nm GaAs laser diode). This field buildup and erasure can be used in a variety of device configurations (one- or two- dimensional arrays, self switching or two wavelength schemes) for opto-optical switching and spatial light modulation applications. These devices can benefit from the large electro-optic coefficient of CdTe (5–6 pV/m) for high contrast polarization switching, or taking advantage of the high electric fields, use the observed Franz-Keldysh electro-absorption which provides large absorption and the associated refractive index changes.
Ultrafast opto-optic switching
Authors: Mehta Sushrut , Fauchet Philippe , Gzara Kais
Published: February 2023

We present a design for an ultrafast optically driven optical switch capable of subpicosecond switching and recovery times. The switch essentially consists of a phased array in which the phase of the light emitted by each element of the array is optically controlled. The distribution of the far field diffraction pattern from such an array can be varied considerably by altering the phase distribution of the array. The extremely short switching times are obtained by utilizing the optical Stark effect, which involves only virtual transitions, and there are no real carriers to restrict recovery times. The switch is also found to be extremely robust against noise as well as partial failure.
Semiconductor optical amplifiers as shutters in photonic switches based on the matrix-vector-multiplier architecture
Authors: Goodman J. W. , Sawchuk A. A. , Dias A. R. , Kalman R. F. , Chau K. K.
Published: February 2023

Several groups have reported the properties of experimental photonic switches based on the matrix-vector multiplier architecture. The shutters in these switches have consisted of a variety of passive materials, such as PLZT, PDLC, and deformable mirror elements. Some switches have been symmetric (same fiber diameter at output and input), some have been asymmetric (larger fiber diameter at output than at input), some have had single-mode inputs, and some have had multimode inputs. The limitations to switch size posed by loss and signal-to-noise considerations for such passive technologies are assessed, including fan-out loss, fan-in loss, and other excess loss. Semiconductor optical amplifiers offer potential improvement of such switches, through faster switching times, lower losses, higher contrast ratios, and high levels of integration. The limitation to switch size posed by noise, particularly spontaneous emission noise, becomes an important question. The increases in switch size afforded by the use of amplifiers are estimated, taking full account of spontanious emission noise. Semiconductor optical amplifiers have been used to construct a 2 × 2 optical crossbar switch with 3 dB of net gain. The amplifiers were angled stripe, gain guided, superluminescent diodes with antireflection coatings (provided by Sarnoff Laboratories). The net gain (including pigtailing loss) for a single device was at best 7 dB. Extinction ratios of 30 dB were merasured and switching times were a few nanoseconds. Assembly of the 2×2 switch yielded a net gain of 3 dB.
All-optical time domain chirp switches
Authors: Islam M. N. , Soccolich C. F. , Chen C.-J.
Published: February 2023

We demonstrate the first all-optical sequential circuit by looping the output from a soliton dragging logic gate1 back to its input. Previously we demonstrated an ultrafast soliton dragging NOR-gate with logic level restoration at the output, fan-out of six, and switching energy of 5.8 pJ. To prove the cascadability and fan-out of the logic gate, we implement a ring oscillator by connecting the NOR-gate as an inverter and adding a feedback loop. The logic gate consists of a 325 m long biréfringent optical fiber surrounded by two polarizing beam splitters. The fiber is carefully laid in a 1 m diameter track and enclosed in an insulating box for thermal stability. A passively mode-locked color center laser supplies the clock pulses (τ = 500 fs, λ = 1.685µm, 54-pJ energy in the fiber) that are coupled along the fast axis of the fiber. We place a 50:50 beam splitter at the output and send half of the output through a delay line and half wave plate to the orthogonally polarized input. The other half of the output is combined with a reference pulse and sent to a cross-correlator. With the feedback blocked the output is a string of l's. When the feedback is added, the output becomes an alternating train of l's and 0's whose period is twice the fiber latency (1.75µs). More complicated functionalities are possible by encoding the clock pulses at the input and decoding at the output.
Traveling-wave laser amplifier measurements in a short-pulse fiber network application
Authors: Erdmann Reinhard K. , Stacy John L. , Krol Mark F.
Published: February 2023

A traveling-wave laser amplifier is a candidate for addressing key issues in very high speed TDMA network applications. Amplification can compensate distribution splitting losses as well as enable direct or indirect threshold detection. Using a cw temperature tuned laser diode, measurements are reported of the gain and the coupling efficiency both with lenses and lensed fibers. Wavelength effects are noted and noise contribution due to super fliorescence is examined. For short pulse application the source laser is replaced by a 1.32-µm mode-locked Nd-YAG in conjunction with a grating pair pulse compressor to yield a pulse train with a repetition rate of 100 MHz and widths of about 1.5 ps. The temporal effects on line-width through the TWLA are measured with a background free autocorrelator. Pulsed gain and gain saturation measurements are reported.
Direct interferometric measurement of the linewidth-enhancement factor in a InGaAsP amplifier
Authors: Ehrhart J. F. , Villeneuve A. , Assanto G. , Stegeman G. I.
Published: February 2023

The linewidth enhancement factor, b, is an important parameter in semiconductor optoelectronic devices. It describes the coupling of carrier induced variations of the real and imaginary parts of the susceptibility. It can be defined as b = -2 k(dn/dN)/(dg/dN) where k is the vacuum wave-vector, n the index of refraction, g the gain, and N the carrier density. The experiment was performed on an index guided InGaAsP/InP buried heterostructure amplifier. We have independently measured the phase change (change in index of refraction) and the gain for different injected currents and different wavelengths. The value of the phase change was determined by the fringe shift in a Mach–Zehnder interferometer. We have optically probed the amplifier using a weak continuous wave probe from a NaCl:OH color-center laser in the wavelength range between 1.50 and 1.58 mm. Initial results will be reported for the b factor as a function of parameters such as wavelength and injected current.
Dissociation energy of hydrogen
Authors: Balakrishnan A. , Smith V. , Stoicheff B. P.
Published: February 2023

The measurement of the dissociation energy of hydrogen remains an important problem in spectroscopy for comparison with theoretical calculations. We report on a preliminary determination of the dissociation energy of H from a fluorescence-excitation spectrum obtained using laser-generated tunable radiation near 85 nm. The radiation was tuned to excite the uppermost vibrational levels of the B state of H and the higher-lying dissociation continuum from the ground state X(v" = 0), while the fluorescence intensity was monitored. Features which were blended in previous work1 are resolved, and they correspond well to predicted2 R(1) and P(1) branches of the X B (v' = 38, 39) transitions, thus confirming Stwalley's identification of lines in the spectrum of H near the dissociation limit of the B state. This limit is then found by extrapolating the P(1) branch positions using Stwalley's technique,2 and from the onset of the dissociation continuum1. The B state dissociates into the products H(1s) + H(2p); therefore, the binding energy of the ground state of H is found by subtracting the Lyman-energy from the B state dissociation limit. From the extrapolation, a value of 36118.6 0.2 cm1 is obtained which agrees with Stwalley's estimate,2 and is 0.5 cm1 higher than a recent theoretical calculation by Kolos et al., and a measurement by Eyler et al. using multiphoton spectroscopy. A less precise value, found from the onset of the continuum, is limited by the presently available resolution.
Boron nitride protective/antireflective coatings for mid-IR wavelength applications
Authors: Biricik V. Warren , Holmes Samuel J.
Published: February 2023

Boron nitride is a hard coating material and is highly transparent in the mid infrared wavelengths. The index of refraction of boron nitride in this wavelength region is dispersive and can be described by a sixth order Pelletier formula. A single layer boron nitride protective/antireflective coating was designed to maximize spectral transmittance over a wide range of angles of incidence using a merit function consisting of a transmission expression averaged over the spectral and angular ranges. The optimized boron nitride protective/antireflective coating on zinc selenide substrates was fabricated using ion beam sputter deposition. The spectral and angle of incidence response of the boron nitride coating was measured and compared with the theoretical calculations employing dispersive index of refraction.
Learning a red–green opponent system from LGN inputs
Authors: Ahumada Albert J.
Published: February 2023

Ahumada and Mulligan1 proposed a network model for constructing a red–green opponent system from LGN outputs without specific long versus middle wavelength cone labeling. They constructed model LGN cells having long and middle cone inputs and fed the LGN outputs into units, presumed cortical, which were trained by a network learning process to compute the principal component of the LGN units in its receptive field. These units turn out approximately doubly opponent and have less luminance sensitivity than their LGN input cells. Their outputs were then calibrated by translation invariance. Derrington, Krauskopf, and Lennie2 and Young3 have published measurements of relative long, middle, and short wavelength cone weightings for actual LGN cells. These weights are sufficient to compute LGN outputs for training the model opponent cells. Model cortical cells were constructed by taking a random sample of seven LGN cells from a data set and computing their principal component weights. The resulting cells are highly red-green opponent (less luminance sensitivity and smaller short wavelength cone weightings). The strong opponency of the LGN cells and the infrequency of large short wavelength weights allows the construction of red-green opponent cells without knowledge of their input sources.
Chromatic adapting effect of achromatic light
Authors: Shevell Steven K. , Wesner Michael F.
Published: February 2023

Consider a small patch of light superimposed on a larger long-wavelength "red" background field. Chromatic adapting effects of the "red" background are well known. We reported recently that the color of the patch is affected additionally by introducing achromatic light surrounding the background (ARVO, 1989). This is surprising because the same achromatic light presented alone (no "red" background) does not change the color of the patch. We consider here the mechanism by which achromatic light alters the color appearance of a remotely located patch. First, the space-averaged illumination in the complete visual field was changed by restricting the achromatic light to only a thin ring, concentric with the central patch but well within and superimposed upon the larger "red" background (1% test patch, 5% background, 12-ft.-wide achromatic ring of diameter 4°). The achromatic ring still caused a large shift in color appearance. Next, the achromatic incremental ring was replaced by a decremental ring (a dark gap) of the same size. The results were very different, indicating the achromatic ring does not merely segment the background field. Next, the achromatic incremental ring was replaced with a "red" incremental ring of somewhat greater luminance. The effect of the "red" ring was much smaller than th«: effect of the achromatic ring. These and other experiments suggest the change in color appearance caused by introducing achromatic light is related to the new information it provides about the range of chromaticities in the visual scene.
Observation of subnatural fluorescence linewidths due to coherent stabilization of quantum fluctuations
Authors: Gauthier Daniel J. , Zhu Yifu , Mossberg T. W.
Published: February 2023

Recently, Narducci et al.1 studied V-configuration three-level atoms and predicted that quantum fluctuations associated with a "strong" optical transition driven by a coherent field can be stabilized through excitation of a coupled "weak" transition. This stabilization is manifest in a narrowing, to subnatural values, of the fluorescence linewidths associated with the strong transition as the weak transition is driven more and more strongly. We have experimentally investigated this problem and provide the first demonstration of the effect. In the experiment, a beam of Ba atoms was intercepted by two copropagating cw laser beams. One of the beams, of Rabi frequency Ω1, was tuned into resonance with the strong, 553.5 nm, 1S0→3P1 transition, while the other beam, of Rabi frequency Ω2, was tuned into resonance with the weak, 791.1 nm, 1S0→3P1 transition. The fluorescence spectrum of the strong transition was recorded for the case when Ω1≈35 MHz and Q2≈45 MHz and, it was found that the spectrum was three-peaked. Most interestingly, the measured linewidth (FWHM) for the central peak was 16 MHz, or 2 MHz less than the 18 MHz natural width of the strong transition even before the substantial instrumental broadening (≈8 MHz) of the peak was deconvolved.
Laser cooling theory of multistate atoms
Authors: Javanainen Juha
Published: February 2023

In the limit of asymptotically small photon momentum, a Fokker–Planck equation for the center-of-mass Wigner function suffices to describe laser cooling of an atom. We have devised a procedure to compute the light pressure force and the diffusion tensor for an atom with an arbitrary level structure, traveling with an arbitrary velocity in any given three-dimensional light field. The scheme is based on solving a set of differential equations closely related to the density matrix equations of motion encountered in conventional recoilless laser spectroscopy. Computer programs have been written that automatically construct and solve the required equations from broad specifications of the problem, such as energies and angular momenta of the atomic levels. A Langevin equation stochastic simulation has been implemented to solve the Fokker-Planck equation of laser cooling using the computed force and diffusion. Comparisons of optical-molasses experiments and simulations carried out for a model sodium atom with a J = 2→J = 3 transition show qualitative similarities such as sub-Doppler limit temperatures, but the quantitative agreement of theory and experiment is not satisfactory.
Robotic fabrication of large f/1.4 parabolas
Authors: Galat-Skey Regina , Hallock Robert , Plotsker Vadim
Published: February 2023

The technology for rapid fabrication of large optical components utilizing robots has recently been perfected at Itek. This paper discusses the steps necessary to fabricate large aperture, f/1.4 parabolas. Raw glass blanks are initially machined to 5-µm rms surfaces. Aspherizing leaves a subsurface damage (SSD) layer of up to 50µm as measured through replication techniques. Robotic loose abrasive grind iterations figure the surface and remove the SSD layer. A 30 machine hour cycle using a 9µm loose abrasive and subaperture tools gives way to several similar uniform removal (DC) microgrind iterations with a 3µm loose abrasive. A surface error map is computed after each cycle using interferometric and profilometric data. The DC removal phase ends when the SSD layer has been minimized. Through an iterative approach, the high areas of the glass are selectively hit. This figuring process yields a 0.1-µm rms surface. Polishing begins in a fashion similar to grinding. Several 50-h cycles remove the microground SSD layerwhile maintaining the surface figure. Next, the part is figured to final specification of 0.02-µm rms. The work has been perfected as Itek has produced this mirror in a total of 46 fabrication days.
Nonlinear, hydrodynamically actuated tools for optical surfacing
Authors: Lee Roger Kenneth
Published: February 2023

Metallic grinding tools have been designed which behave similarly to unstable hydrodynamically lubricated bearings. Tool suspension geometry has been arranged so that negative angles of attack occur when the tool traverses a workpiece using a viscous slurry of diamonds in the micrometer size ranges. The negative attack angle causes a large suction pressure equal to the vapor pressure of the slurry between the tool and the workpiece. Under proper conditions, the tool force is independent of velocity, and the pressure is independent of the tool contact area. The result is a tool that works completely to edges without roll off, and which is suitable for working lightweight waffle structures without print-through. The grinding rates obtained are comparable to those obtained with #100 silicon carbide at the same velocity. A specular surface finish is produced which is suitable for interferometry. The tools have been used to surface a square mirror, and an off-axis parabola of lightweight construction. An optician working by hand, has been able to remove 7 µm per hour on a 0.75 m2 pie-shaped optic. The principal application problems concern the large lateral shear forces produced on lightweight structures, and the possibility of inclusions in the tool metal causing occasional scratches.
Statistical study of beam replication in stimulated Raman scattering
Authors: Hilfer Godehard
Published: February 2023

Experimental work on Raman beam cleanup and beam combining has long been confounded by the generation of parasitic Stokes side beams. It has been found experimentally that when the pump beams are moderately aberrated, Stokes beams which propagate along the pump beams are generated. This effect is referred to as side beam replication. By contrast, when the pump beams are strongly aberrated, 24 × diffraction limited, no replication is observed. We can attribute this phenomenon to scintillation of the pump intensity. When the diffraction scale length is large compared to the gain length then the Stokes noise propagating col- linearly with an aberrated pump beam will experience larger gain than the central, seeded Stokes beam in the regions where the pump beam intensity is higher than average. As the aberrations increase, the gain of the side beams increases at first, maximizing at χ ~ 4 (χ diffraction limited), and then decreases again due to the decrease in diffraction length. The output energy of the central Stokes decreases because diffraction causes the pump beams to spread, so that they become less efficient at amplifying the Stokes beams. Replication is strongest for moderate aberrations, χ ~ 4, in which the scintillation mechanism is predominant. In this case, we observe a spread of the output side beam intensities of over four orders of magnitude, due to the sensitive dependence of the amplification on the detailed pump beam scintillation pattern. For strong aberrations, the total side beam intensity and its variation decreases strongly. At aberration numbers χ > 20, intensity mixing due to diffraction effectively suppresses beam replication.
Noise characteristics in a low-light-level Raman amplifier
Authors: Reintjes J. , Duncan M. D. , Mahon R. , Tankersley L. L.
Published: February 2023

We have previously reported experimental results of Raman amplification of a low light level seed Stokes beam in the transient limit.1 Here we present results of measurements done using a 10 ns seed-injected, single spectral mode, Nd:YAG laser. The 532 nm frequency-doubled output has a duration of 8.5 ns and is used both to generate a 4.5 ns duration seed-Stokes pulse at 683 nm and to pump the 1 m long Raman amplifier. The seed-Stokes beam is spatially filtered and apertured at the Airy minimum and is collimated before the amplifier at a size corresponding to a Fresnel number adjustable over the range of 5-30. Likewise, the spatial mode of the pump is optimized to be as smooth as possible and is collimated and the plane of the doubling crystal is imaged into the Raman amplifier with Fresnel number of 2-15. For unseeded operation, the typical random patterns characteristic of the quantum-noise initiated, self-generated Stokes light are observed. We find that for a Fresnel number 2 pump beam and a gain of 107, the output of the amplifier is controlled with a signal to noise ratio of about 15 when the seed-Stokes energy is about 170 aJ (560 photons). When the pump beam diameter is increased to give a Fresnel number of 15, similar control of the output is obtained with a seed-Stokes level of 7 fJ (2.3 × 104 photons) at a gain of 106. Further experiments will be conducted to identify the influence of Fresnel number and Raman gain on the seed level needed to exert control over the spatial modes of the output Stokes.
Atmospheric Raman thresholds for power and fluence of a linearly polarized laser
Authors: Krapchev Vladimir B.
Published: February 2023

The rotational Raman gain in N2 is evaluated, taking into account the Stokes-antiStokes coupling1 for linearly polarized light and the dispersion of the refractive index of the air. A significant reduction of the gain coefficient near the phase matching angle increases the threshold intensities for peak powers of less than 10 GW. The maximum laser power for atmospheric propagation in steady state, and the maximum fluence for a transient Raman gain are evaluated for diffraction limited beam propagation achieved by phase compensation for turbulence.
Observation of parametric hyper-Raman scattering in an organic crystal
Authors: Wang Q. Z. , Ho P. P. , Alfano R. R. , Kashyap R.
Published: February 2023

Nonlinear optical materials based on π-conjugated organic monomer and polymer materials have the potential to possess extremely large and fast nonlinear coefficients. The organic crystal (−)2-(α-methyl-benzylamino)-5-nitropyridine (MBA-NP) has attracted much interest because of its high optical damage threshold and extremely large χ(2). We report on the observation of nonlinear optical effect of parametric hyper-Raman scattering in an ultra thin MBA-NP crystal. The nonlinear spectrum under 1054 nm excitation from 300-600 nm indicated that there are four distinct maxima located at 527 nm, about 560 nm, 351 nm, and about 364 nm. The signal at 527 nm and 351 nm are the second and third harmonic generations, respectively. Two new features are located at about 560 nm and 364 nm, which are shifted by phonon frequency from second and third harmonic generation signals, respectively. These signals may be from the parametric generation of the pump laser and its Raman scattering. A parametric instability theory is extended to quantitatively explain these experimental results.
Refined design techniques for practical antireflection coatings with a very broad bandwidth
Authors: Willey R. R.
Published: February 2023

We have reported1 the development of a new viewpoint in AR coating design using inhomogeneous index (Rugate) functions. We have carried this to the practical application of the design principles to films composed of only homogeneous layers using two materials. Here we refine these applications by the use of three and four different practical indices. We discuss the possibilities and we demonstrate the limitations of the currently available indices (particularly low indices). The "ideal" broad band AR would have a smooth index profile from the substrate to the medium. This can be approximated by the use of many thin homogeneous layers. The major limitation is the need for a last layer of lower index than currently available. This causes the residual reflectance in the AR band to be higher than desired and/or the band width to be significantly narrower. We show how far these limits can be pushed in practical coatings with current materials.
Performance Evaluation of a Ground-based Lidar System
Authors: Gomez-Mendoza R.
Published: February 2023

This paper describes the performance of a lidar system prototype applied to atmospheric sulfur dioxide assessment from oil-fired power plant emis sions. This work was aimed to test the behaviour under integral operation at field, in order to identify the trend of future development.
Layers that contribute to atmospheric turbulence
Authors: Walters D. L.
Published: February 2023

Optical turbulence degrades large aperture, ground based telescope systems. In general, hundreds of individual layers contribute to this degradation; however, the spatial distribution of these layers is not random. Over the last decade, microthermal probe, acoustic sounder, and optical measurements reveal that frequently a few layers contribute most of the degradation. We find consistencies in the surface, boundary, and tropopause layers that assist in predicting their magnitudes and occurrences. Since the physical phenomena producing these layers are different, knowledge of the spatial and temporal distribution is beneficial in developing large aperture, ground based telescope systems.
Innovative adaptive optics using a membrane light modulator: a single-pixel demonstration
Authors: Mitchell P. V. , Gaeta C. J. , White J. O. , O'Meara T. R. , Pepper D. M. , Shiller C. M. , Horsky T. N. , Warde C.
Published: February 2023

We report on the demonstration of an all-optical closed-loop adaptive optical compensation system using a membrane light modulator1 (MLM) as the corrector device. A typical MLM consists of a large array of highly reflective, deformable membrane pixels that are driven electrostatically via optical or electrical addressing. The device can therefore impose a phase shift onto a pixelized input beam, controlling the reflected beam’s wavefront.
Possibilities for projection x-ray lithography using holographic optical elements
Authors: Jacobsen C. , Howells M. R.
Published: February 2023

Projection x-ray lithography has received considerable attention recently as a way of pushing circuit feature size below the level at which proximity printing schemes become problematic. However, the optical figure tolerances for the projection systems usually discussed are well beyond the current state of the art. We consider the use of computer-generated holograms for printing circuit features. One scheme involves the use of an off-axis phase hologram written as surface height variations on a grazing incidence optical flat. Another scheme we have studied extensively through computer simulations involves the use of a transmission mask with material thickness variations designed in such a way that the magnitude and phase of the transmitted wavefield is controlled to produce the desired pattern with low noise and high contrast. Both schemes involve only modest extensions of existing technologies, and offer a route to x-ray projection lithography of sub-0.1-µm circuit features.
Optoelectronic relational algebraic processor
Authors: Marsden Gary C. , Shaneyfelt Ted , Esener Sadik , Lee Sing H.
Published: February 2023

The dual scale topology optoelectronic processor (DSTOP) was developed for generalized matrix algebra.1 Vector outer products are a particularly useful feature of the DSTOP architecture. Since the computation is performed electronically, a generalized function may be substituted for conventional numerical multiplication; this is especially useful in symbolic computations such as those required in relational databases. We have developed algorithms appropriate for DSTOP that use generalized outer products in the execution of relational algebraic operations.2 The DSTOP processor serves as a decision subsystem in a relational database machine. The DSTOP relational algebraic processor is well suited to interface with 3D optical storage devices such as optical disks, photorefractive crystals or two-photon memories. The operations performed include joins, set difference, union, intersection and set division. Duplicate removal may also be performed in the support of the projection relational operator. The remaining relational operators, selection and Cartesian product, are not included. Cartesian products require no decision mechanism while selection, which is a unary operator, is best performed on a smaller, front end processor.
S-SEED based programmable logic array
Authors: Derstine M. W. , Babbitt W. R. , Bell J. A. , Capron B. A.
Published: February 2023

A promising candidate for logic arrays in optical cellular logic image processors is the symmetric self-electrooptic effect device (S-SEED). We describe the operation of an 8 × 16 array of S-SEEDs as programmable logic gates operating using the time sequential scheme described by Lentine et al.1 with a space multiplexed beam combination technique.2 The programmable gate operates at an effective rate >10 kHz which is limited by the speed of the computer drive, and >80% of the gates operate correctly simultaneously. The beam combination scheme used in this system requires that several different image planes be focussed onto the SEED array.
Conditional higher-order modified signed-digit symbolic substitution using trinary arithmetic
Authors: Alam M. S. , Karim M. A. , Awwal A. A. S. , Westerkamp J. J.
Published: February 2023

Among the higher radix number systems, the trinary modified signed-digit (MSD) arithmetic appears to be the most promising in terms of both optical processing elements and storage complexity.1 The MSD system involves two processing steps which can be optically implemented using the recognition and substitution phases of symbolic substitution. Recently, Kozaitis2 and Eichmann et al.3 demonstrated higher-order SS based addition schemes that allow longer operands to be processed at the same time. However, the processing time for these SS schemes is still a function of the operand length. To overcome these problems, we propose a conditional higher-order trinary MSD SS scheme. In this technique, the two-step arithmetic operations (addition and subtraction) achieved are independent of the operand length. The necessary SS rules for addition (subtraction) is made carry-free (borrow-free) by checking a pair of reference bits from the next lower order bit so that there are no two identical nonzero MSD digits in any column. This scheme is efficient in terms of memory requirement since more information can be incorporated in fewer digits. Finally, a content addressable memory based optical implementation of the trinary MSD SS scheme is also presented.
Approach to optical symbolic substitution using a lenslet array
Authors: Matsushita K. , Kajiki Y. , Shimizu E. , Yu Francis T. S. , Yang Xiang Y.
Published: February 2023

A lenslet array can shift and overlap input patterns at the image plane in an appropriate arrangement. By utilizing this nature of the lenslet array, a simple optical symbolic substitution system has been constructed. The lenslet array is arranged symmetrically to the search pattern and placed behind the input pattern in the recognition phase. Then the superimposed patterns corresponding to the lenslet arrangement are formed at the image plane. The location of the search pattern corresponds to the maximum intensity position of the superimposed patterns. By thresholding the superimposed intensity, the binary pattern indicating the location of the search pattern can be recognized. A similar optical arrangement is useful in substitution phase. The lenslet array is placed according to the substitution rule and forms the superimposed pattern of the detected search patterns, which represent the replacing pattern.