bluuebunny/crossref_metadata_2025 huggingface dataset:
Fourier-transform IR emission observations of combustion systems
Authors: Annen K. D. , Wormhoudt J.
Published: February 2023

Measurement of infrared emission from hot-gas sources can be a useful method of determining temperatures and molecular species concentrations. Widening applications stem from two developments: the recent availability of commercial Fourier-transform infrared (FTIR) spectrometers that are relatively lightweight, rugged, and easy to operate, and the existence of computer programs that can readily predict changes in emission spectra with changes in source parameters. This new generation of FTIR spectrometers makes possible a wide variety of laboratory measurements that are nonintrusive, demand relatively little modification of the system being observed, and are easy to carry out. On the other hand, substantial analysis of the resulting spectra is required before quantitative estimates of system parameters can be made. We will give examples of what can be learned from emission spectra, focusing on three combustion systems: a large liquid-spray flame, a burning strand of solid rocket propellant, and the exhaust gas from apartment-building furnace stacks.
Rough-surface scalar inverse scattering within the Rytov approximation
Authors: Schatzberg Alon , Devaney Anthony J.
Published: February 2023

A classical method for rough-surface scattering is the field-perturbation (Born) approximation. A recently proposed method,1 the so-called phase-perturbation method, has been shown to possess advantages over the Born approximation. In that method a powerseries perturbation expansion is applied to the phase of the induced surface-source function, which is the unknown in an integral equation representing the extinction theorem. It is known now that this phase power series converges more rapidly than the conventional (Born) field power series. This is true particularly in the high frequency limit, i.e., when the wavelength of the incident field is small relative to the length scale associated with the surface-roughness function. This phase-perturbation approach to scattering, however, is not known to possess an inverse. In our work we directly evaluate the scattered field at a plane in the vicinity of the scattering boundary, rather than the induced source function. Within the first-order phase-perturbation approximation, the above field is found to be related to the surface-roughness function in a simple manner, which is also invertible.
Analysis of ballistic electron transport in semiconductor quantum-well waveguides
Authors: Wilson Daniel W. , Glytsis Elias N. , Gaylord Thomas K.
Published: February 2023

The wave nature of ballistic (collisionless) electrons in semiconductor quantum wells is treated. Reflection of an electron from a single potential barrier is analyzed as a function of the electron's incident angle and kinetic energy. Results include critical angle for total reflection, wave-function phase shift on reflection, and lateral (Goos–Hanchen) shift parallel to the barrier on reflection.
Relationship of electromagnetic reflection and refraction to quantum-mechanical transport in semiconductor heterostructures
Authors: Henderson Gregory N. , Glytsis Elias N. , Gaylord Thomas K.
Published: February 2023

Electromagnetic reflection and refraction at a boundary between lossless dielectrics is well known for commonly available materials with differing permittivity (ε) and the same permeability (µ). In this case, the expressions for the reflectivity of TE and TM polarizations have different functional forms with a Brewster angle for TM polarization but not for TE polarization. For an interface between generalized dielectrics (differing ε and µ), the TE and TM reflectivities have the same form where one, both, or neither of the polarizations can have a Brewster angle. By defining separate phase and amplitude indices, common expressions can be used for the TE and TM reflectivities.
Semiconductor claddings on glass waveguides for polarizers and detectors
Authors: Veasey David L. , Larson Donald R. , Phelan Robert J. , Batchman Theodore E.
Published: February 2023

The efficient transfer of energy from dielectric regions to semiconductor-clad regions in semiconductor-clad dielectric waveguides is of paramount importance to the operation of waveguide polarizers and detectors. We have experimentally shown that the coupling of energy from dielectric guiding regions to semiconductor-clad regions is highly dependent on cladding thickness and polarization. Accurate tuning of cladding thicknesses allows for the selective attenuation of either TM- or TE-polarized waves, but the opposite polarization (TE or TM, respectively) passes with minimal loss. This effect lends itself well to the fabrication of waveguide polarizers and detectors that respond to only one incident polarization.
Real-time, near-field optical microscopy
Authors: Mansfield Scott M. , Kino G. S.
Published: February 2023

A real-time near-field optical microscope (RNOM) has been developed that is capable of 80 nm resolution with visible light. Previous near-field optical microscopes imaged through a tiny pinhole placed very close to the sample and used mechanical scanning. The RNOM operates in real time, has a good light budget, and can be added to a standard or real-time confocal microscope. The principle of the RNOM is similar to that of an oil-immersion microscope, in which the transverse resolution is improved by a factor of n, the refractive index of the oil. The RNOM uses a solid immersion lens (SIL) placed between a long-working-distance objective and the sample to achieve a corresponding improvement. Because good optical materials can be found with indices as great as 3.4, the RNOM achieves better resolutions than a liquid-immersion system and can be used to image inside solid materials with refractive indices close to that of the SIL. We have used the RNOM with an n = 2 SIL to image 160 nm lines and spaces. The experimental edge response of the system is twice that of the confocal microscope.
Coupled-cavity resonant-passive mode-locked Ti:sapphire laser
Authors: Keller U. , Knox W. H. , Roskos H.
Published: February 2023

Coupled-cavity resonant passive modelocking (RPM) is a new simple technique to passively mode-lock laser media that have a small gain saturation cross section, such as a Ti:sapphire laser.1 We simply added an external matched cavity with a nonlinear GaAs/GaAlAs quantum-well reflector to a cw pumped Spectra Physics Ti:sapphire laser.
Extended tuning range for a passively mode-locked NaCl color-center laser
Authors: Soccolich C. E. , Islam M. N. , German K. R.
Published: February 2023

We have doubled the tuning range of a passively mode-locked NaCl color-center laser by introducing a low-loss intracavity frequency filter and properly preparing the NaCl gain crystal. By using a collection of bulk and multiple-quantum-well III–V saturable absorbers and II–VI quantum-well saturable absorbers, we obtained passive mode-locked operation over the wavelength range of 1.5–1.7 µm. To provide sufficient wavelength restriction without introducing excess bandwidth limiting or loss, we replaced the biréfringent plate of previous systems1 with a tunable frequency filter,2 formed by a pair of equilateral flint glass prisms (spaced 22 cm apart) and followed by a knife edge. We tune the laser by horizontal translation of the knife edge. The laser produces pedestal-free, near-transform-limited 280 fs pulses, which is the same pulse width obtained with birefringent plates. To obtain lasing at wavelengths shorter than 1.51 µm, the NaCl YAG crystal must be annealed to reduce scattering from presence of colloidal particles formed during coloration. With annealed crystals we obtain lasing at wavelengths as short as 1.38 µm, and laser power at 1.5 µm is only 30% below the maximum. In summary, we demonstrate a stable, single-cavity solidstate, subpicosecond pulse source of 1.5–1.7 µm.
Quantum measurement theory of photoelectric detection
Authors: Carmichael H. J.
Published: February 2023

The criterion used to distinguish classical from nonclassical effects in quantum optics is based on the theory of photoelectric detection. In the semiclassical theory of photoelectric detection, the optical field enters as a stochastic intensity. Results obtained from the quantum theory can be reproduced within this stochastic formalism whenever the quantum state of the field is a statistical mixture of coherent states. When the quantum state of the field is not of this form, certain statistical properties of the observed photocurrents and photopulse sequences cannot be reproduced within the semiclassical formalism.
Quantum-noise reduction with a Q-switched laser
Authors: Aytür Orhan , Kumar Prem
Published: February 2023

Pulsed squeezed light and intensity-correlated twin beams are generated by means of a traveling-wave optical parametric amplifier (OPA) consisting of a type-II phase-matched KTiOPO4 crystal that is pumped by a Q-switched and frequency-doubled Nd:YAG laser. Q switching of the laser results in a high peak pump intensity and a large peak parametric gain. Squeezed light is generated by amplifying the vacuum input field to the OPA, and it is detected by a balanced homodyne configuration that uses the fundamental beam of the laser as a local oscillator.1 Twin beams are generated by supplying a small input signal to the OPA. The amplified signal and idler beams are direct-detected individually and yield quantum-noise reduction when the two photocurrents are subtracted.
Three-dimensional nature of the confocal spread function
Authors: Schack Roland
Published: February 2023

This paper deals with the development of the concept of a three-dimensional spread function as an aid in understanding the reconstructed image obtained in scanning confocal microscopy.
Radiative properties of liquid-water and ice clouds
Authors: Pilewskie Peter
Published: February 2023

Most clouds in the lower and middle troposphere are optically thick to the extent that their pattern of scattered radiation bears little resemblance to the scattering pattern from a single water droplet or ice crystal. Photons at visible and near-infrared wavelengths that emerge from a thick cloud have been, on average, scattered several times and retain little memory of the angular dependence or even particle-shape dependence of scattering from a single particle. Indeed, single-scattering phenomena, such as the halo and corona, are not visible from optically thick clouds. However, even though most of the angular and wavelength dependencies of single scattering are washed away, radiation reflected by and transmitted through a thick cloud still holds clues to the cloud's physical makeup. Cloud particle thermodynamic phase and size, cloud optical depth, and water path can, at least in principle, be derived from the measurement of near-infrared spectral reflectance or transmittance because of the dependence of absorption in clouds on particle size and bulk water absorption coefficient. Thus far, efforts to infer cloud properties by means of near-infrared remote sensing have had only limited success.
New approach to optimizing computer-generated holograms
Authors: Ersoy O. K. , Brede J.
Published: February 2023

Computer-generated holograms are often optimized by error diffusion, projections onto constraint sets (POCS), and direct binary search. We introduce a new method based on interlacing a number of subholograms; each subhologram is optimized by using the POCS to correct the remaining reconstruction error. In addition, once all the subholograms are used, the remaining error is recirculated through all the subholograms until minimum reconstruction error is achieved. A number of experimental results with binary computer-generated holograms indicate that the reconstruction error is reduced to half that which is possible with the POCS method alone.
New method for degenerate four-wave mixing for the generation of phase-conjugate waves in photorefractive crystals
Authors: Zhang He-Yi
Published: February 2023

We report a simpler method for degenerate four-wave mixing photorefractive crystals in which only one pump beam and one probe beam incident to the crystal is necessary to generate the phase-conjugate waves.
Multilevel quantization of images with error diffusion
Authors: Broja Manfred , Bryngdahl Olof
Published: February 2023

The error correction and diffusion algorithm is a powerful and constructive binarization process, and it can be modified to accomplish a multiple-level quantization. Such a modification makes additional free parameters available for optimization of the process. We will show how quantization noise can be modified by proper choice of threshold levels. Our experiments illustrate how low-contrast details of the image are upgraded by the process.
Injection locking a Q-switched standing-wave alexandrite laser with a frequency-stabilized diode laser
Authors: Glesne Thomas R. , Zukowski Barbara J. K. , Czechanski James P. , Kay Richard B.
Published: February 2023

An AlGaAs diode laser at 760 nm is frequency stabilized to a molecular-oxygen absorption line and is used to injection lock a Q-switched alexandrite laser, which will be used as a lidar source in the remote sensing of atmospheric pressure and temperature. The diode laser operates nominally at 761 nm. Temperature tuning to the absorption feature of interest is accomplished by externally adjusting a temperature-bias voltage to the diode controller. Active frequency stabilization is achieved through photoacoustic feedback by frequency dithering the diode through an oxygen cell. Stabilization to less than 15 MHz has been reported. Successful injection locking of the broadband standingwave alexandrite laser has resulted in a linewidth of less than 500 MHz in an 85 ns pulse, 20 mJ/pulse, 5 pps.
Vertical cavity surface-emitting microlasers
Authors: Jewell J. L. , Scherer A. , Lee Y. H. , McCall S. L. , Harbison J. P. , Florez L. T. , Tucker R. S. , Burrus C. A. , Sandroff C. J. , Olsson N. A.
Published: February 2023

Electrically driven microlasers are attractive as elements of photonic switches, photonic chip-to-chip communications systems, or matrix-addressable light source arrays. Fabrication of more than one million lasers on a <1 cm chip, submilliampere threshold, 8-GHz modulation, and more recent progress will be discussed.
Reduction of spontaneous noise in ring laser sensors
Authors: Lai M. , Diels J.-C.
Published: February 2023

It has recently become possible to manufacture laser media consisting of thin layers that are each thinner than the wavelength of light. The semiconductor versions are multiple-quantum-well lasers, also called surface emitters. Other lasers that can be built with this structure are stoichiometric lasers. It is shown that a ring laser can be made with this structure in a configuration such that the spontaneous (laser) noise is interferometrically subtracted and hence not detected. For applications, such as rotation-sensing of magnetic fields, it is necessary to eliminate the strong coupling between counterpropagating waves owing to the nature (thin films) of the emitter. Solutions to this problem involving either intracavity or extracavity passive elements are presented. Other applications require the laser to be unidirectional. This goal can be achieved by adding a single reflecting layer to the active stack of emitters.
Analysis of glass waveguides with etched grating
Authors: Lamouche Guy , Li Ming-Jun , Najafi S. Iraj
Published: February 2023

Grating-assisted waveguides are integrated optics devices potentially useful in sensor, communication and signal processing applications. To design such devices with specific performance characteristics, an accurate theoretical tool to predict their optical behavior is essential. In this work, we have analyzed ion-exchanged channel waveguides with grating. We first use the finite-difference method to determine the index profile of the ion-exchanged glass waveguides. We employ a modified Crank-Nicholsen scheme called Altemating-Direction-Implicit method to solve the interdiffusion problem and to calculate the index profile. Then, we employ the scaler finite-element (FEM) to solve the scaler wave equiation and to calculate propagation constants and mode profiles of hte waveguides modes. We use four-node rectangular elements with bilinear approximation functions. The eigenvalue problem is solved using a simultaneous iteration technique. Finally, the coupled-mode theory is employed to analyze the channel waveguides with grating. The grating is treated as a perturbation of the waveguide on which it is fabricated. The details of calculation and the effect of different device parameters on waveguide behavior will be discussed.
Charge-coupled devices in the XUV and soft-x-ray regions
Authors: Michels D. J. , Howard R. A. , Catura R. C.
Published: February 2023

The charge-coupled device (CCD) can be used to detect photons at wavelengths from the near UV infrared down to the x-ray region. In this paper we review the development of CCDs with respect to quantum efficiency and imaging characteristics for XUV and x-ray wavelengths. In the XUV region—15-50 nm—the CCD must be used in back-illuminated mode because the gate structures grown on the front side are completely opaque at these wavelengths. This requires that the imaging area of the backside be thinned to approximately the depth of the depletion region (about 10 µm), as the penetration technologies have been developed for thinning the device. Physical conditions in the backside surface oxide play an important role in the ability of the device to collect signal photoelectrons in the depletion region. For example, trapped positive charge creates a potential barrier that can inhibit collection of the signal photoelectrons. Ion implementation has been successfully used to modify back surface potentials, permitting useful detective quantum efficiencies throughout the XUV and soft-x-ray regions.
Low-noise charge-coupled device camera for soft-x-ray imaging
Authors: McNulty Ian
Published: February 2023

We have developed an inexpensive, low-noise, high-resolution charge-coupled device (CCD) camera for imaging applications in the soft-x-ray region. It is capable of photon counting, and because it is cryogenically cooled, it can achieve integration times of several hours. A P31 phosphor coating on the CCD active surface downconverts incident x-rays with high efficiency and no loss in spatial resolution. The aluminum camera body is kept under moderate vacuum (1–10 mTorr) by a sorption pump for thermal insulation and unimpeded propagation of x rays to the detector plane. An aluminum coated Si3N4 entrance window delivers acceptable throughput down to 200 eV x-ray energies and effectively blocks external visible-light sources. The internal 0.8 L liquid-nitrogen Dewar flask maintains the detector substrate at –125°C by means of a flexible copper cold finger for ~10 h under ambient conditions. A slow-scan CCD sequencing and sampling circuit based on a CAMAC system provides standard image erasure, integration, and readout functions under computer control. Data-acquisition software permits convenient user manipulation of camera operating parameters as well as on-line image display. Our characterization of the CCD camera with 350 eV x-rays indicates good performance at 1 photon/pixel•s rates.
Effects of measures of similarity on neural nets
Authors: Arsenault Henri H. , Sheng Hunlong , Lejeune Claude
Published: February 2023

Objects are usually stored in neural networks as sets of weights on synapses that multiply input values. For convenience, the stored and input values are often set equal to the binary values 1 and 0. Using instead 1 and –1, as in the Hamming model, often yields improved network performance. However, because input objects do not usually contain negative values, input values of 1 and –1 ordinarily require preprocessing of the input data.
Ion-exchanged glass waveguides with etched gratings
Authors: Li M. J. , Albert J. , Najafi S. I. , Wang W. J. , Hill K. O.
Published: February 2023

Channel waveguides with gratings are useful components in the fabrication of integrated-optic devices. For example, they can be used to couple lights into or out of the waveguides for out-of-plane interconnects, or they can be used to filter selected wavelengths in wavelength-division multiplexing systems.
All-optical phase-locked modulator
Authors: Whitaker Norman A. , Houh H. H. , Avramopoulos H.
Published: February 2023

An all-fiber erbium-glass laser has been mode locked using an optically-controllable Sagnac loop mirror. By tuning the cavity length of the control laser, cw oscillation of the erbium laser has been observed at frequencies up to 13.8 GHz.
Optical modifications to a scanning laser ophthalmoscope for high-magnification, narrow optical section imaging
Authors: Fitzke F. W. , Timberlake G. , Woon W. H. , Marshall J. , Bird A. C.
Published: February 2023

A lens system was designed and incorporated into a prototype Rodenstock scanninglaser ophthalmoscope, which provided additional magnification of retinal structures and further narrowing of optical sections. The lens system increased the effective numerical aperture of the eye. In addition, smaller pinholes were used for the confocal aperture. The optical-section thickness was measured by using an artificial eye and positioning an artificial retina near the plane of focus under micrometer control. The digitized images were averaged over a central area of 16 × 16 pixels, and intensity was measured as a function of "retinal" position. The results showed that sections with half-widths < 70μm could be achieved. An infrared diodelaser was used to image the living human retina with this system. The maximum retinal irradiance was calculated to be within the standards of the American National Standards Institute. High-magnification images of the retina were acquired at different section depths. These results suggest that it is possible to image the microscopic structure of the living human retina. This may be useful in characterizing and studying microanatomical and functional alterations (measured by high-resolution SLO perimetry) in the human retina.
Modeling of atmospheric and cloud polarization by using space shuttle imagery
Authors: Egan Walter G. , Sidran Miriam
Published: February 2023

Space-shuttle imagery on mission STS-28 (August 20, 1989) shows a significant atmospheric-polarization effect (20-30%), which decreases as the sensing wavelength decreases. The imagery was acquired over the central United States (New Madrid, Missouri, area) in the red, green, and blue spectral regions. It appeared that the unusual polarization variation is a result of atmospheric aerosols. The Hansen-Travis vector-doubling model was used to characterize the atmospheric polarization effects. A uniform sandy surface area adjacent to the Mississippi River was used to calibrate the measurements. The polarimetric properties of a smoke plume from a coal-fired electrical plant in the same area were also imaged and modeled. The combination of a small atmospheric polarization with earth-surface polarization was analyzed by neglecting multiple scattering between the two. The atmospheric polarization was modeled with the doubling technique and was linearly combined with the earth-surface polarization to obtain the remotely sensed polarization.
Blurring of underwater generated signals owing to surface waves
Authors: Chang Enson , Patton Randy J.
Published: February 2023

The blurring of an underwater-generated signal by its transmission through a wavy air-water interface is often ignored in radiative-transfer calculations. This paper treats the effect statistically (assuming a Gaussian distribution of surface-wave slopes) and as a function of wind speed. Surface refraction, Fresnel-transmission coefficient, and signal broadening from underwater propagation are included in the calculation. The results show that surface-wave-induced blurring can be significant for long integration times, even at moderate wind speeds.
IR absorption coefficients of CFC-12 and CFC-22
Authors: Varanasi Prasad
Published: February 2023

Infrared line positions of many chlorofluorocarbons are difficult to catalog because the lines are densely packed. Lines belonging to hot bands and isotopic bands further complicate the problem. It is desirable to measure the absorption coefficient itself over the range of wave numbers, temperatures, and pressures that are appropriate to remote sensing experiments in the atmosphere. Because the ultimate goal in any lineby-line scheme is to compute the absorption coefficient, kv, a computation that can be flawed by our lack of knowledge of all the spectroscopic parameters governing line absorption and of their temperature and pressure dependence, why not measure the absorption coefficient directly in the laboratory?
Ray matrices for rays around a general skew ray
Authors: Zabel M. , Collins S. A. , Evans E. D.
Published: February 2023

Ray matrices for rays whose directions are close to that of a base ray that can be any general skew ray are derived and examined. The derivation starts with Hamilton's characteristic function; the resulting refraction matrix has a simple interpretation in terms of Coddington's equations. A computer raytracing program is required to provide angles of incidence and refraction and direction cosines for surface normals and ray directions. The derivations and some simple applications will be presented.
Space-time sharing optical neural network
Authors: Yu Francis T. S. , Lu Taiwei , Yang Xiang Y.
Published: February 2023

The massive interconnection and parallel operation in an optical neural network (ONN) require a high-resolution, large-dynamic-range spatial light modulator (SLM) for the construction of the interconnectionweight matrix (IWM). However, the resolution of currently available SLM's is limited, and this is a major obstacle in the development of a large-scale optical neural computers. We use a space-time-sharing technique to improve the resolution of an optical neural operation. Because the ONN we recently developed1 uses incoherent light, the space–bandwidth product of the network can be expanded by space-time multiplexing. In other words, a large-scale neural operation can be accomplished with a smaller network, by trading off the processing speed. To accomplish this task, we have shown that a large-scale IWM can be partitioned into arrays of sub-IWM's, of which the space–bandwidth product of the sub-IWM's is equal to the number of neurons in the neural network. Then by sequentially displaying these arrays of sub-IWM's, a larger (nfold) space–bandwidth image pattern can be obtained by using a smaller ONN. Computer-simulated results and experimental demonstrations are also provided in this paper.
Degenerate four-wave mixing in Kerr media in the presence of nonlinear refraction, pump depletion, and linear absorption
Authors: Guha Shekhar , Conner Philip
Published: February 2023

We consider degenerate four-wave mixing in a Kerr medium with a standard noncollinear geometry and the polarization directions of all the beams parallel to one another. The two pump beams, the probe beam, and the phase-conjugate beam are denoted by the subscripts 1,2,4 and 3, respectively. The nonlinear medium is placed between z = 0 and z = 1; the values of the intensities of the beams at z = 0 and 1 are denoted by Ii0 andIi1, where i = 1,2,3,4. Beams 2 and 4 are incident at z = 1; and beam 1 is incident at z = 0. We have determined the dependence of the phase-conjugate reflectivity R = I31/I41 and the pump transmission T = I11/I10 on the following parameters: the probe ratio, q=I41/(I10 + I21); the pump ratio, r = I21/I
1
0; the absorption coefficient–path length product, al; and the coupling constant of the medium, q. In the absence of nonlinear refraction, pump depletion, and linear absorption in the medium, R = tan2q. When all of these effects are taken into account, the maximum value of R is given by Rmax = exp (-2α1)/(q(1 + r)). The minimum value that T can reach is proportional to q for q < 1. Even for small values of q, multistable solutions for R and T are obtained when q is greater than a threshold value, which we denote by qth. We have determined the dependence of qth on the parameters q and r.
Incoherent light four-wave mixing for the measurement of reorientational relaxation of dye molecules
Authors: Yu Yi-Zhong
Published: February 2023

I present a new convenient optical phaseconjugation technique for measurement of ultrafast reorientational relaxation time (T) in the study of dye solutions. This new method uses temporally incoherent light instead of short pulses. This method is different from those appropriate to optical Kerr media.
Compact in-line laser radial-shear interferometer
Authors: Shukla R. P. , Moghbel M. , George M. C. , Venkateswarlu P.
Published: February 2023

Various optical arrangements to obtain radial shear in a converging beam of laser light are presented. The interferometer is made of a cube-type beam splitter such that two opposite surfaces are generated with different curvatures and the entrance and exit surfaces are in the same line. A wave front under test is focused into the center of the beam splitter. The reflected light from the beam splitter is again focused onto the beam splitter after reflections from two spherical surfaces of the cube. Finally, the beam travels in the same direction as that of direct transmitted beam, but with a change in numerical aperture. Consequently, two wave fronts are radially sheared to produce an interference pattern. The interferometer is compact and simple to make. Its alignment is easy because the incident test wave front is in line with the sheared wave fronts. Aberrations are introduced into the interferometer by the spherical nature of the curved surfaces, and aberration analysis is also presented. Some applications of the interferometer for testing lenses and assessing the quality of emerging wave fronts from the exit-slit of a monochromator are also suggested.
Structural and optical nonlinear properties of CdSxSe1-x-doped glass films
Authors: Chenard Francois , Jerominek Hubert , Tremblay Réal
Published: February 2023

We present the fabrication procedure and material characterizations of semiconductor microcrystallite-doped glass films made by the cosputtering of Corning 7059 and CdxSSe1-x. Based onx-ray photoelectron spectroscopy, the chemical composition of the deposited films was evaluated. The presence of the semiconductor crystallites was verified by Raman spectroscopy. Transmission electron microscopy (TEM) studies revealed that the average microcrystallite diameters ranged from 3 to 5 nm. The semiconductor crystallites grow with the temperature of the postdeposition thermal treatment. This was directly verified by TEM measurements and was indirectly verified by a blue shift of the transmission and luminescence spectra. The refractive index and absorption coefficient have been measured with ellipsometric and prism-coupling techniques. The results are shown for several wavelengths.
Generation of Sub-100 Femtosecond Pulses Tunable in the 690-750 nm Range
Authors: Becker P.C. , Cruz C.H. Brito , Prosser A.G.
Published: February 2023

We report the generation of tunable femtosecond pulses in the 690-750 nm wavelength region, by selective continuum amplification and subsequent recompression, in a CPM based ultrashort pulse system. The continuum is generated in a jet of ethylene glycol with amplified CPM pulses at 620 nm. The amplified continuum pulses are typically of duration 75-85 femtoseconds (assuming a sech2 profile) with energies per pulse of several microjoules, at a repetition rate of 8.5 kHz. The pump source for the amplifier is a copper vapor laser. The dyes used as the gain medium for the continuum amplifier are LDS 698 and LDS 750, which, even though they are significantly less efficient than Rhodamine or Styryl 9, accomplish the desired purpose. These pulses are then launched in a 10 mm length of single mode fiber to produce a broad spectral continuum which is then compressed to pulses of duration 12-13 femtoseconds. Ultrashort pulses in this wavelength range will be useful for resonant investigations of quantum well structures.
Nonlinear absorption studies in metallophthalocyanines
Authors: Wei T. H. , Sence M. J. , vanStryland E. W. , Hagan D. J. , Ferry J. W. , Coulter D. R. , Khundkar L. R.
Published: February 2023

Solutions of metallophthalocyanines and metallonaphthalocyanines have recently attracted attention because of the large optical nonlinearities observed in these materials. These nonlinearities arise from the fact that the materials possess a delocalized electronic system confined in the macrocyclic ring plane. The linear absorption spectrum of these systems exhibits two sets of absorptions bands, which are associated with the transitions in the macrocyclic ring system. In addition, these compounds exhibit an excited-state absorption in the energy range between the Q- and B-bands, where the linear absorption is weak. This absorption can be ascribed at short times to the Sl-Sn and at long times to the Tl-Tn absorption. Transmission and Z-scan measurements have been performed on solutions of chloro-aluminum- phthalocyanines (CAP) in methanol, and a silicon naphthalocyanine derivative (SiNc) in toluene, by using 30 ps pulses at 532 nm. We determined the singlet-singlet absorption cross-sections to be 4 × 10−17 cm2 for CAP and 5 × 10−17 cm2 for SiNc. We also used trains of 10 of these pulses separated by 7 ns. These latter measurements clearly show a cumulative effect that demonstrates the effect of the triplet-triplet absorption at longer times. From the Z-scan results we calculated n2 values of 3.3 × 10−12 esu for CAP and 4 × 10−12 esu for SiNc for concentrations of 6 × 10−4 mol/1.
Use of the biased estimator in the interpretation of spectroscopic ellipsometry data
Authors: Jellison G. E.
Published: February 2023

Generally, spectroscopic ellipsometry data are compared with a model of the sample surface by using a nonlinear least-squares fitting procedure to determine characteristics of the surface, which include thin-film thickness and fractions of individual constituents in the layers. Usually, an unbiased estimator (i.e., without any spectroscopic weighting) is minimized to determine the parameters of the fit. In this paper, the use of the biased estimator in the fitting of spectroscopic ellipsometry data is examined and is applied to data from two-channel polarization modulation ellipsometry experiments. By including the error in the estimator, the more accurate regions of the spectrum are weighted more, and the ellipsometric data can be expressed in the most appropriate way (i.e., as complex P, W and A, complex e) without affecting the results of the fit. In addition, a goodness-of-fit can be calculated, which indicates whether a more complicated model is necessary or whether competing models are statistically different. Several thin films of SiC>2 on Si will be discussed as examples.
A flip-flop thin-film design program with enhanced capabilities
Authors: Dobrowolski J. A. , Kemp R. A.
Published: February 2023

In the original flip-flop method for the design of optical thin-film systems, a starting design consists of many thin layers of equal thickness. A solution is sought that is based on two nonabsorbing, nondispersive materials. The design process is controlled with the aid of a merit function. This function is defined in terms of the desired transmittances at different wavelengths. The optimum solution is found through the repeated selection, taking each layer in turn, of the material that gives rise to the greatest improvement of the merit function. In this talk a more advanced version of the program is described, which makes possible a more elaborate specification of the desired performance is possible. The program has been modified to allow for the dispersion of the coating materials. The selection is made from three, not two, materials, one of which may be a metal. These changes greatly increase the types of problems that may be solved by this technique. The method is demonstrated on a number of different problems.
Linear analysis of eccentricity-dependent changes in the null-based isoluminant plane
Authors: Lindsey Delwin T.
Published: February 2023

The percept of motion that is elicited by moving gratings is lost at isoluminance when the stimulus is viewed continuously. This loss of motion perception was used to evaluate variations with retinal eccentricity in the spectral sensitivity of the motion mechanism, nulled at isoluminance. Subjects viewed 2.3° square, 1.3 cpd, 3.75 Hz moving gratings generated by a color cathode-ray tube. These stimuli were used to estimate the motion null plane foveally and at 2,4, and 8°. The orientations (in three-dimensional color space) of the best-fitting null planes were determined by principal component analysis. The orientation of the foveal isoluminant plane differed from that obtained at 2, 4, and 8°. The variation in orientation with eccentricity was further analyzed by expressing the null planes as linear combinations of two eccentricity-dependent vectors: one calculated fora macular pigment-absorption template of variable density and the other calculated for variable linear combinations of L- and M-cone absorption spectra. The analysis suggests that most of the eccentricity-dependent differences in spectral sensitivity should be attributed to variations in macular pigment density across the retina and not to changes in relative L-and M-cone contributions to the motion mechanism nulled at isoluminance.
Jones Matrix Analysis of read during write signals in magnetaoptic disks
Authors: Mendez Antonio J. , Bergthold Patricia , Garmire Elsa
Published: February 2023

Magneto-optic disks based on rare-earth transition-metal thin films exhibit a polarization signal during the Curie point writing process. We identify the potential sources of this signal by means of a Jones matrix analysis.
Scattering from symmetric surfaces and surfaces perpendicular to a mirror
Authors: Ponce M. A. , Mendez E. R. , Ruiz V.
Published: February 2023

Recent theoretical and experimental results on light scattering from randomly rough surfaces have shown the importance of coherent effects in the presence of multiple scattering and symmetries. These coherent effects give rise to enhancements in the back-scattering, antispecular, or specular directions. Here, we present some recent experimental results of scattering from one-dimensional randomly rough surfaces with an even profile and from two-dimensional rough surfaces perpendicular to a mirror. These systems produce, respectively, enhanced specular and enhanced backscattering phenomena and are closely related. The similarities and differences between the two cases will be discussed, and, where possible, theoretical curves will be presented. The fabrication and characterization of the symmetric surfaces in photoresist will also be described.
Fourier-transform spectroscopy of van der Waals molecules
Authors: McKellar R. W.
Published: February 2023

Summary not available at press time.
Massively parallel optical template matcher/correlator
Authors: Mok Fai , Tackitt Michael , Stoll Harold M.
Published: February 2023

Many proposed architectures for optical pattern-recognition use large space–bandwidth template matching. Experience gained in the last 10 years or so of research indicates that a large number of templates/filters are required in order for most applications to be practical. Traditionally, optical-correlation techniques have relied on templates/filters being either serially presented in time or spatially multiplexed in two dimensions. For many applications, the former approach is penalized by excessive time–overhead, whereas the latter approach requires an unrealistically large space–bandwidth product. In this paper, we describe the architecture and functioning of a massively parallel optical template matcher/correlator capable of calculating the inner products of 1,000 high-space–bandwidth pattern vectors simultaneously. Our template matcher/correlator consists of a large number of angle-multiplexed, Fourier-space volume holograms stored in a LiNbO3:Fe crystal. Each hologram is stored by exposing the LiNbO3 crystal to the interference pattern of one of the templates/filters to be stored and to a plane wave. Each plane wave has a slightly different (horizontal) angle of incidence for each hologram. All templates/filters, however, are incident at the same angle, Θ. When an input image illuminates the crystal at angle Θ, partial reconstructions of the stored plane waves, each proportional to the cross correlations of the input image with the stored templates/filters, emerge from the crystal. These plane waves are then focused by a spherical lens to form a one-dimensional array of pattern vector inner products and cross correlations (with one-dimensional shift invariance) in the orthogonal dimension. We have experimentally generated the covariance matrix for a 1000- template/filter device and have found good agreement with the corresponding, numerically generated matrix.
Effect of errors in optical correlators
Authors: Ma Paul W. , Reid Max B. , Downie John D.
Published: February 2023

Given the interest in optical binary phase-only correlation implemented with magnetooptic spatial light modulators, an understanding of the effect of errors in system alignment and optical components is critical in obtaining optimum system performance. We present simulations of performance degradation in the presence of six errors divided into three groups. Under the first group, system errors, we simulate both translational and rotational misalignment of the input mask with the filter mask. Because system errors are mainly alignment errors, they are largely controllable by the designer. Next, we have errors that are partially controllable by the designer, which result from a combination of system and component nonidealities. These include a scale error caused by an incorrect focal length of the first set of transform lenses and an error in phase compensation owing to inexact component placement and lens focal length. Last, we have component errors that are not controllable by the designer, which result from the choice of spatial light modulator. These include imperfect contrast in both the input and filter masks and phase errors caused by the nonuniform flatness of the masks. The effects of each individual error are discussed, and the result of combining all six errors, under assumptions of reasonable tolerances and system parameters, are also presented. Conclusions are drawn as to which tolerances are most critical for optimum system performance.
Fisher information as the basis for relativistic quantum mechanics
Authors: Frieden B. Roy
Published: February 2023

The Klein–Gordon equation for spinless particles, as well as the Weyl–Pauli and Dirac equations for particles with spin, may be derived from one information-theoretic principle. Consider a gedanken experiment whereby the mean position of a particle in a central force field is to be estimated by means of one position measurement. An efficient (optimum) estimate obeys a condition of minimum Fisher information, or minimum precision, according to the second law of thermodynamics. When the Fisher information is minimized subject to a constraint on the mean-square kinetic energy for the particle, the solution is a probability law on position whose corresponding wave amplitude obeys the Klein-Gordon equation, the Weyl–Pauli equation, or the Dirac equation, depending on whether scalar (without spin) or vector (with spin) solutions are sought. The minimized Fisher information is proportional to the mean-square kinetic energy, minus the rest energy of the particle.
Highly efficient cw 2-μm laser
Authors: Kintz Gregory J.
Published: February 2023

Thuilium doped laser hosts are studied for high-power cw 2-μm lasers. When we used a Ti:Al2O3 laser as a pump source for a Tm:YAG laser, 1.2 W of 2-μm laser output was observed with 2.8 W of pump power. The effects of energy transfer on laser performance will be modeled.
Trio upconversion laser
Authors: Xie Ping , Rand S. C.
Published: February 2023

An efficiency of nearly 30% has been achieved in an erbium upconversion laser operating at 0.85μm with excitation at 1.5μm. Continuous-wave excitation of fluorescence from the upper laser level is shown to vary as the cue of the pump intensity, and time-resolved studies are used to distinguish between various multiphoton and multiatom processes that potentially contribute to the population inversion. We have been able to show that the inversion is overwhelmingly dominated by a three-body cooperative process, which we refer to as triopumping. The high efficiency of this continuous-wave trio laser is particularly remarkable in view of its operation on a self-terminating transition with lower laser-level pumping.
Measurement of the third-order susceptibility of organic molecules
Authors: Tackx Peter , Persoons André
Published: February 2023

The intensity of the optical phase conjugated (OPC) wave in a degenerate four wave mixing (DFWM) experiment in a measure of the third order nonlinear susceptibility. To obtain accurate measurements, we constructed a modified Michelson interferometer with a conjugate mirror in each arm. The first conjugate mirror is made out of a reference cell with carbondisulfide pumped in the back-reflection mode; the sample cell with the organic dye-solution is placed in the second arm and forms the other conjugate mirror. A piezo-electric translator moves one arm of the interferometer resulting in two interference patterns: one from the OPC-signal and one from the pump-signal. The modulation of the OPC interference pattern is a measure of the ratio of the susceptibilities of the two media. The phase shift between the two interference patterns determines the sign of the third order susceptibility of the sample. We measured the third order hyperpolarisability of trans-stilbene (STIL), 1,6-diphenylhexatriene (DPH) and 4-methoxy-4′-nitrostilbene (MONS). We found the following values: 2.9E-33 esu (STIL), 67E-33 esu (DPH) and 210E-33 esu (MONS). All these susceptibilities have the same sign, opposite to the susceptibility of carbondisulfide.
Third-order nonlinear susceptibility at 1053 nm of a series of ester- and tolane-linked liquid-crystal naphthyl compounds
Authors: Schmid A. , Marshall K. , Puchebner B. , Li Z. W. , Chuang Y. H. , Meyerhofer D.
Published: February 2023

Picosecond, chirped-pulse technology is used to generate spectrally separate (Δ = 16 Ǻ), time-synchronized pulses for non-resonant χ(3) measurements near 1053 nm by nearly-degenerate four-wave mixing. This background-free technique is applied to eight newly synthesized monomeric liquid-crystal structures based on naphthyl cores and alkylphenyl moieties linked by ester or tolane linkages. The design of these compounds permits a systematic study of the role of electron delocalization pathways in determining the magnitude of χ(3) in such organic systems. Measured χ(3) values are normalized to χ(3) of CS2. The advantages of liquid-crystalline macroscopic order in device fabrication from these promising compounds are discussed.