bluuebunny/crossref_metadata_2025 huggingface dataset:
Production of optical thin films using molecular beam deposition technology
Authors: Fisher S. P. , Hale C. C. H. , Muirhead I. T. , Mathew J. G. H.
Published: February 2023

Earlier research indicated that optical thin films deposited by molecular beam deposition (MBD) techniques exhibit refractive indices approaching bulk material values and have densities higher than those of conventional thermally deposited films.1 These superior characteristics provide very stable films with an increased laser damage threshold. A new MBD machine was recently purchased from VG Semicon and modified by OCLI to provide commercially available MBD optical coatings. The new system, a V90H, was developed for the semiconductor industry to produce high quality epitaxial GaAs films in production quantities. Investigations are proceeding on numerous materials used in diverse optical applications. Single layer studies of various chalcogenides and fluorides, including ZnSe, ZnS, BaF2, and PbF2, on typical optical substrates (glass, quartz, sapphire, and silicon) confirm that improved film properties are consistently achieved. The V90H provides a thickness uniformity of ~±0.2% over a 4-in. diam substrate which is a significant improvement from previous MBD systems. The highly stable MBD process combined with automated control allows the deposition of innovative multilayer optical designs with a precisely varying index of refraction throughout the thickness of the film.
Optical nonlinearity in thin films of amorphous arsenic sulfide
Authors: True Emily M. , Mccaughan Leon
Published: February 2023

Bulk chalcogenide glass semiconductors have been shown to exhibit a large, yet fast absorption nonlinearity.1 The greatly broadened absorption edge characteristic of these amorphous semiconductors offer the possibility for large dynamic optical nonlinearities over a much larger range of wavelengths than found in crystalline materials. In addition, amorphous semiconductors are attractive for optical device applications because they can be deposited easily on a variety of substrates. Thin films of amorphous arsenic sulfide, a chalcogenide glass semiconductor, have been deposited on quartz and silicon substrates by ion beam sputtering. This method of deposition produces films which are amorphous, smooth, and of excellent optical quality. Preliminary measurements using a cw pump-probe technique show that, unlike in crystalline materials, where bandfilling effects cause a decrease in absorption, the absorption increases with pump intensity over a broad range of probe wavelengths. As in the bulk,1 the mechanism responsible for this effect is believed to be a result of structural disorder. Intraband transitions of a type forbidden in crystalline materials cause an increase in absorption at low energies when conduction band tail states are filled by bandgap energy radiation. Quantitative measurements of the change in the absorption spectrum of these films as a function of pump intensity and pump wavelength are presented.
Hybrid refractive-diffractive superachromatic lens
Authors: Mercado R. I. , Foo L. D. , Clark S. P.
Published: February 2023

The design, manufacture, and applications over wide spectral bands of hybrid refractive-diffractive lenses have been addressed recently by several authors.1,2 Although it is fairly easy to design an achromatic hybrid lens, its optical performance is often limited by secondary color and spherochromatism. We recently achieved superachromatic designs of hybrid lenses with finite thicknesses that are color corrected at four wavelengths over a wide band covering the visible and near infrared regions of the electromagnetic spectrum.
Polarization properties of focusing grating couplers
Authors: Griffin Devon W. , Weller-Brophy Laura A.
Published: February 2023

A focusing grating coupler consists of a chirped, curved grating on the surface of a dielectric waveguiding structure. Due to the geometry of the grating rulings, such a coupler can convert a guided waveguide mode to a radiation mode having a point focus above or below the plane of the waveguide. Such focusing couplers have been proposed as the central coupling and focusing elements in CD ROMS and magnetooptic disk drives. In spite of these applications, little detailed study of their polarization properties has been presented in the literature. In this presentation we discuss the polarization properties of focusing grating couplers. Based on the local normal mode theory of waveguide gratings, we have analyzed the coupling induced by the grating between orthogonal polarization components for the case of radiation modes. The analysis is based on an extension of the ray trace method of Heitmann and Ortiz1 and implementing the coupling strengths for guided to radiation mode coupling obtained from local normal mode theory. The method produces a near field amplitude which is propagated to the far field using Huygens-Fresnel theory. Resultant far field spot profiles are presented and implications for appropriate use of focusing grating couplers in integrated optical systems are discussed.
Bragg reflection waveguide based directional couplers
Authors: Lenz G. , Salzman J.
Published: February 2023

Bragg reflection waveguides (BRWs), consisting of a guiding layer (core) surrounded by periodic media (claddings), exhibit a unique dispersion relation, resulting in a forbidden and allowed band structure.1 We recently proposed a novel directional coupler consisting of two such BRWs in close proximity.2 Here we analyze the coupling properties of the BRW directional coupler. To obtain the modal profiles of the proposed structure, we first derive its characteristic equation and solve for the propagation constant β± for the two fundamental modes. Proceeding with a perturbation analysis we find an explicit analytic expression for the coupling constant κ
.
The coupling constant decreases exponentially with the separation of the guides (similar to that of conventional couplers), with a decay constant characteristic of the dispersion relation of the periodic medium in the coupling region. Comparing the expression for κ in a conventional directional coupler to the one we derived, we find some novel properties: (i) The effective width of the core (accounted by the Goos-Haenschen shift) may be smaller than the physical width; (ii) for the same core separation the coupling constant is much larger; this can be viewed as effective shrinking of the optical path by the periodic coupling section; and (iii) since the decay constant is a function of both refractive indices of the periodic medium, the coupling constant may be tuned electrooptically or even detuned (with consequent destruction of the confined guiding).
Multiprocessor design using polarization-encoded optical shadow-casting
Authors: Awwal Abdul Ahad S. , Karim Mohammad A.
Published: February 2023

In this work, the polarization-encoded optical shadow-casting (POSC) algorithm for designing a parallel multiprocessor is described. As an example, we have used the POSC algorithm to design a combined adder-subtracter. Unlike the all-electronic digital adder/subtracters, this multiprocessor provides the outputs of both addition and subtraction simultaneously without any increase in the system hardware.1 This multiprocessor is the first of its kind reported in the optical computing literature. Further, this design points out an important distinction of optical digital system design as follows: In digital systems, the number of gate inputs as well as the number of gates are reduced by using a Karnaugh map.2 But in the optical shadowcasting scheme, the simplification of the logic circuit is achieved by the sharing of minterms.1 In digital electronics, such minterm sharing is usually not attempted. The design of this parallel multiple-output dual-addressable multiprocessor memory device is very attractive as it saves memory by 50% or more. The proposed device gives out parallel output bits and is highly efficient when compared with its electronic counterpart.
Focal spot smoothing experiments on the Vulcan glass laser system
Authors: Danson C. N. , Bann R. , Pepler D. , Rizvi N. , Ross I. , Afsharrad T. , Coe S. , Desselberger M. , Willi O.
Published: February 2023

Laser/plasma interaction experiments have generally suffered from poor focal spot quality. This problem is a direct result of the coherence of the laser. A number of different methods1,2 have been developed to modify the coherence properties of the laser in an attempt to produce a smooth focal spot profile. In designing a scheme suitable for Vulcan a number of constraints have to be considered: the laser system must remain flexible to meet the needs of a broad based user community; the focal spot requirements differ significantly between the different groups and all have to be catered to; and the cost of any scheme has to be limited. The method chosen was a combination of induced spatial incoherence (ISI) and random phase plates (RPP). To produce ISI a short coherence length oscillator is used. To generate spatial incoherence transparent echelons are placed at the output of the rod amplifier chain before the final disk amplifier stages. This method as used on Vulcan has a limit on the size of focal spots available. A second smoothing method is therefore used: RPPs are inserted into each beam to control the divergence of the laser. This hybrid approach to focal smoothing has proved extremely successful.
Patterned quantum well semiconductor lasers
Authors: Kapon E. , Harbison J. P. , Bhat R. , Hwang D. M.
Published: February 2023

Lateral patterning of the bandgap in semiconductor quantum well (QW) lasers is essential for achieving lateral carrier confinement and for integrating diode lasers with other optoelectronic components having a different bandgap. In particular, lateral carrier confinement into extremely narrow (<0.1 µm) dimensions is required for the realization of low-dimensional quantum wire and quantum dot lasers. We have developed a new technique for lateral patterning of semiconductor QW lasers.1 The technique consists of growing otherwise conventional QW laser structures on patterned, nonplanar substrates. The resulting patterned QW heterostructures exhibit lateral variations in the effective QW bandgap. Patterned QW lasers grown by molecular beam epitaxy2 have active region widths of ~1 µm and exhibit threshold currents as low as 0.7 mA. Patterned QW lasers grown by organometallic chemical vapor deposition have crescent-shaped quantum wire active regions <0.1 µm wide. Lasing due to transitions between quasi 1-D subbands in these quantum wires has been observed.3
FM responses of two-electrode DFB lasers
Authors: Twu Y. , Dutta N. K. , Wynn J. D. , Kuo C. Y. , Wagner E. J.
Published: February 2023

Progress in multigigabit optical fiber transmission systems has advanced significantly over the past few years. Uniform, high sensitivity, and wide bandwidth frequency modulation (FM) are essential in semiconductor laser based angular modulated coherent optical fiber communication systems. Two-electrode DFB lasers (2E-DFB) show great potentials for all the requirements mentioned above. We report in this paper a study of the FM responses of two-electrode DFB lasers vs the condition that one section (front) is biased to obtain lasing action whereas the other (back) section is moderately biased and modulated.1
Photorefractive integrated-optical switch arrays in LiNbO3
Authors: Aronson Lewis B. , Hesselink Lambertus
Published: February 2023

Optical interconnects for highly parallel computer architecture require high density optical switch arrays with dimensions of 100 × 100 or larger. Previously reported integrated switch array designs have been limited to 8 × 8 waveguides.1 While achieving high switching speeds and relatively low insertion losses, these switches are limited by long interaction lengths which lead to array dimensions of as long as 60 mm. Our switch design consists of two sets of parallel waveguides which intersect at right angles. The intersections are doped with a material to locally sensitize the region to the photorefractive effect. We have fabricated arrays based on standard Ti:LiNbO3 technology, using iron as a photorefractive sensitizer. Interfering beams are used to write an index grating at the waveguide intersections. This grating can then be used to diffract a portion of a data beam into the crossing waveguide. The diffraction efficiency depends on the length of the interaction region. Thus, insertion loss is traded off against switch density. We have constructed arrays of 15 × 15 up to 50 × 50 waveguides in an active area of only 5 mm square.
Partially resolved rotational structure in the photoacoustic spectrum of I2
Authors: Venkateswarlu Putcha , Chakrapani G. , Abdeldayem H. , Okafor C. , George M. C.
Published: February 2023

We reported recently1 a partially resolved rotational structure representing the [(14,2), (12,1)] and [(13,2), (11,1)] bands in the photoacoustic spectrum of I2 due to

X
1

Σ
g
+

−

B
3

I
I

(

0
u
+

)

transition. We now report a similar structure in the 16,900–17,000-cm–1 region representing the [(13,1),(15,2)] bands. The spectrum is recorded with the photoacoustic spectrometer reported earlier.2 A comparison of the photoacoustic spectrum with the absorption spectrum in the I2 atlas of Gerstenkor and Luc helped in its analysis. Vibrational-rotational energy transfers in the B and X states are probably responsible for the photoacoustic spectrum. The rotational lines [P(57), R(52)] of the band (13,1) and [P(49), R(54)] of (15,2) expected around 16,962.4 cm–1 and a similar group expected around 16,911.5 cm–1 are nearly extinct. This suggests that molecules reaching the corresponding upper levels do not transfer their energy to the medium. Possible mechanisms such as multiphoton ionization and fluorescence to υ″ = 0 from these levels are discussed to understand this observation.
Photoacoustic spectrum (17,750-18,960 cm–1) of Br2
Authors: Venkateswarlu Putcha , Chakrapani G. , George M. C. , Henry M.
Published: February 2023

Kumar et al.
1
recorded the photoacoustic spectrum (16,100-17,400 cm–1) of Br2 using a flashlamp pumped dye laser. We recorded here the spectrum in the 17,840–18,900-cm–1 region using an excimer laser pumped tunable dye laser and a photoacoustic spectrometer recently assembled.2 Optogalvanic spectrum of Ne is used for wavelength standards. Partial pressure of Br2 is ~250 Torr and that of air is 510 Torr. This spectrum involves the transition

X
1

Σ
g
+

→

B
3

I
I

(

0
u
+

)

with (18 ≤ V ≤ 49) and (0 ≤ V" ≤ 5). Nonradiative vibrational-rotational energy transfers in B and X states are responsible for the photoacoustic spectrum. High values of υ" are reached by fluorescence from the B state and they go to lower levels only by nonradiative energy transfers as Br2 is homonuclear. The result is that V" = 4 and 5 are well populated at room temperature although the corresponding Boltz-mann factor for these levels is not high.
Quantitative tests of cortical visual receptive field models
Authors: Young Richard A.
Published: February 2023

Young1 first proposed the Gaussian derivative and DOOG (difference-of-offset-gaussians) models to describe the 2-D spatial structure of visual simple cell receptive fields in primate cortex. The Gabor model has also been proposed to describe such physiological data. Although tests of all three models have previously been made for neural 1-D spatial frequency tuning curves,1 I now report preliminary tests on recent 2-D cortical visual receptive field data measured directly in the spatial domain.2 I also report on the effects of the temporal dimension on the fits of these models. This study was undertaken in collaboration with L. Jacobson, J. Gaska, H.-W. Chen, and D. Pollen at the University of Massachusetts Medical Center, who kindly provided the monkey cortical receptive field data.
Fabry-Perot interferometer misalignment: the effect on image plane tilt
Authors: Goad Joseph H. , Romanczyk Kazmere C. , Engle Charles D.
Published: February 2023

Many papers have been published on the imaging effects in Fabry-Perot interferometers. Hodgkinson and Vukusic1 have published the effects of secondary fringes that exist when the interference fringes are not focused. McMillan2 described the effects of fringe shift and of multiple source fringe splitting that is caused by misalignment. While observing Fabry-Perot fringes through a microscope, we found that the effects of plate misalignment could be corrected by tilting the microscope image plane to match the interferometer image tilt. Slight misalignment causes large image plane tilts that are related to the interferometer plate separation and the interferometer finesse. In our application, the interferometer was inaccessible in a vacuum chamber. By tilting our observation plane at the interferometer image plane outside the chamber, acceptable data could be obtained without taking the chamber apart to realign the interferometer.
Wavelength division multiplexers with large number of channels
Authors: Moslehi Behzad , Jannson Tomasz , Vendura George J. , Harvey Phil
Published: February 2023

Wavelength division multiplexers (WDMs) with a large number of channels and extremely low cross-coupling losses (less than −35 dB), based on holographic optical elements in 3-D and planar geometries are proposed. The basic architecture of holographic WDMs consists of volume holograms in 3-D or waveguide geometry. Based on the optical performance of high efficiency holographic technology1 developed at POC, the losses per channel can be <1 dB. The number of channels in both multiplexing and demultiplexing modes can exceed ten with channel separation between 10 and 30 nm. The multichannel WDMs with low loss and low crosstalk are particularly desirable in the next-generation fiber optics local area network applications.
Subtractive processes in light adaptation
Authors: Hayhoe Mary M. , Levin M.
Published: February 2023

Subtractive mechanisms have been clearly established as playing an important role in light adaptation. Unlike gain control mechanisms, subtractive mechanisms remove the steady state signal from an adapting background without attenuating the response to incremental flashes. Little is known about the time course or neural basis of such mechanisms. Previous measurements1 indicated that a large component of the subtractive change occurred effectively instantaneously at light onset but the rest of the change was quite slow, taking a second or two to complete. In this experiment we extended the measurements to get a more complete description of the time course of the subtractive component. Several different adapting background intensities and a small step, comparable to that in normal scenes, were examined. We also manipulated the spatial configuration of the display to test whether some component of the rapid subtractive change resulted from lateral inhibition. The experiment was performed in foveal vision, measuring threshold for a brief red incremental probe at the onset of a white flashed field. The adaptational state was manipulated by an additional white field. With large fields, there was no subtractive change for several hundred milliseconds unlike previous findings, and the process took 10-15 s to asymptote. It seems likely that the fast component previously observed results from center-surround antagonism.
Polarization properties of phase conjugation utilizing atomic two-photon resonances
Authors: Kauranen Martti , Gauthier Daniel J. , Malcuit Michelle S. , Boyd Robert W.
Published: February 2023

It is often desirable that a phase conjugate mirror be able to correct for polarization distortions in addition to correcting for wavefront aberrations. Such a device is called a vector phase conjugate mirror. It has been predicted within the context of the third-order theory that vector phase conjugation can be achieved by degenerate four-wave mixing using atomic two-photon transitions between S-states.1 We recently developed a theory of the polarization properties of two-photon resonantly enhanced degenerate four-wave mixing which can treat saturation effects due to pump waves.2 Our results show that for the case of linear and parallel pump wave polarizations, vector phase conjugation occurs with high quality and high reflectivity for two-photon transitions for which the nonresonant Stark shift is very small. We have also found that for the case of circular and counterrotating pump wave polarizations, perfect vector phase conjugation occurs for equal pump wave intensities. We have studied experimentally the effects of saturation and Stark shifts for S → S two-photon transitions of atomic sodium. We have found that high fidelity vector phase conjugation can be obtained.
Second harmonic generation in optical fibers: modal and nonmodal phase matching
Authors: Kashyap Raman , Lucek J. K. , Williams D. L. , Davey S. T.
Published: February 2023

Ouelette et al.1 recently demonstrated the erasure, subsequent to the seeding with 532- and 1064-nm wavelength light, of the self-organized grating in an optical fiber by further illumination with 532-nm light alone. We have demonstrated second harmonic generation of 1064-nm radiation in modally phase matched fibers2 by prior treatment with argon laser radiation alone. In this paper we report experimental results on a modally phase matched and untreated (by argon laser radiation) fiber. First, it was seeded by injecting a small amount of 532-nm wavelength radiation simultaneously with 1064-nm wavelength radiation. Subsequently, transmission with 1064-nm wavelength radiation generated frequency doubled light in the seeding mode as reported in Ref. 1. This seeded mode interaction is generally believed to be phase matched by a self-organized χ(2) grating written into the fiber. Subsequent illumination with higher power 532-nm wavelength light and further probing with 1064-nm wavelength radiation alone showed the disappearance of the seeded frequency doubled mode and thus erasure of the grating, but also the appearance of the modally phase matched interaction. Our experiments highlight the differences in the nature of the phase matching processes in optical fibers. In Ref. 1 it is speculated that charge recombination occurs during the erasure process. Our experiments show that this is more likely not the case and that the model proposed by Payne,3 in which a uniform transverse internal field is created as a result of illumination with visible radiation, is partly responsible for second harmonic generation in modally phase matched fibers.
Intensity-dependent phase mismatch of second harmonic generation in optical fiber
Authors: Ouellette François
Published: February 2023

We report measurements of the second harmonic dependence on the input fundamental light power in optical fibers possessing a χ(2) induced by seeding.1 Our results are explained by including self-phase and cross-phase modulation (SPM and CPM) in the equations governing second harmonic generation. The index changes due to SPM and CPM do not cancel out and result in an intensity-dependent phase mismatch, whose strength also depends on the relative polarizations of the fundamental and second harmonic lights. During the seeding stage, this effect detunes the χ(2) grating toward negative phase mismatch. When generating the second harmonic through such a detuned χ(2) grating, the intensity-dependent term first brings the interaction closer to exact phase matching, resulting in a more than quadratic dependence of second harmonic power on the input power. At very high intensity, the induced phase mismatch becomes positive at the peak of the pulses and frequency conversion saturates. The polarization dependence of the saturation is also discussed.
Achromatic volume holography using dispersive compensation for grating tilt
Authors: Cronin-Golomb Mark
Published: February 2023

A method for recording achromatic volume holograms is described. These are of interest for their high diffraction efficiency and ability to be realized in real time using nonlinear optics. Such volume holograms may be used in applications including image reconstruction, distortion compensation, and phase conjugation. The polychromatic object field passes through a fixed tilted grating. A telescope images the undiffracted and first-order beams onto the holographic recording medium tilted by the same angle as the fixed grating. Proper tilt of the dispersive recording medium makes the system volume achromatic and the fixed grating tilt makes the system achromatic at the surface of the recording medium. In a typical experiment a 5-mm thick crystal of photorefractive barium titanate might be used. The undiffracted portion of the beam is spatially filtered so that it may be used as a plane wave reference beam. Alternatively, if there is a point source in the object field everything else in the field may be filtered out of the undiffracted beam so that the undiffracted beam may be used as a reference beam to cancel phase aberrations of the exterior system. This is similar to previous monochromatic experiments in which a reference beam is passed through the same distortion as the object beam so that a distortion compensated hologram may be written.1
Spatial variability as a limiting factor in texture discrimination tasks
Authors: Sagi Dov , Rubenstein Barton S.
Published: February 2023

Human texture discrimination seems to be limited to measurements of local differences across receptive field (RF) activities. Important RF properties include spatial frequency and orientation selectivity, where each RF generates a filtered map of the input image. Significant local differences within each map can be taken as evidence for texture boundaries. A model that combines odd and even symmetry RF maps, generating energy maps, produces discrimination values that correlate well with human performance.1 Here we consider the role of spatial noise (internal and external) in filtered maps as a performance limiting factor. We show that external noise, mainly due to randomization of texture parameters (like orientation), creates spurious local differences in the filtered maps (due to their orientation selectivity). This noise level depends on the particular texture element (e.g., its rotational symmetry) and may have a stronger distractive effect when it is large in the background. When quantified, this improved model accounts for asymmetry in human texture discrimination performance.2
Number state preparation in a micromaser
Authors: Walther Herbert
Published: February 2023

Experiments with the one-atom maser1 have demonstrated that it is possible to study the interaction of a single atom with a single-mode of a resonant electromagnetic field in a cavity. The atoms used in these experiments are Rydberg atoms with a very large principal quantum number. Another important ingredient is the superconducting cavity: The quality factor is high enough for a periodic energy exchange between atom and cavity field to be observed; i.e., the relaxation time of the cavity field is larger than the characteristic time of the atom-field interaction, which is given by the reciprocal of the Rabi frequency. It is therefore possible to perform experiments on the dynamics of the atom-field interaction. Some of the features are explicitly a consequence of the quantum nature of the electromagnetic field.2 With a new cavity (quality factor 3 × 1010) it could be demonstrated that the statistics of the photons in the cavity is sub-Poissonian; in suitable conditions it is even possible to generate number states. Using number states of the single-atom maser novel quantum interference experiments can be performed giving new insight in the wave particle duality.
Parametric DFB resonator, squeezing, and Unruh radiation
Authors: Haus Hermann A.
Published: February 2023

An accelerated mirror generates photons from vacuum. This process is known as Unruh radiation.1 A uniform distribution of dielectric sheets spaced much less than a wavelength apart produces a net change in the effective index. When the sheets are displaced in a spatially periodic manner, a grating is formed. Motion of the sheets results in a time dependent (parametrically varying) grating that can produce squeezing. In this configuration, the squeezing is ascribed to Unruh radiation. A field analysis of moving dielectric sheets in the background of the zero-point fluctuation field is presented in this paper and shown to correspond to the Unruh formula. Recently, Yablonovitch proposed to use laser-generated exploding plasmas to simulate an accelerating mirror surface.2 We propose another simulation of accelerating mirrors with laser light that could lead to a laboratory experiment. If a grating is produced in a nonlinear fiber ring resonator, with one port of the 50/50 beam splitter fed by the pump, the other used as the signal port, the Unruh radiation emerges from the signal port and the pump is separated out automatically.
Matrix FTIR spectroscopy of transient species
Authors: Andrews Lester
Published: February 2023

Matrix studies featuring the FTIR instrumental advantages of resolution and sensitivity for a finite amount of time are described. Ammonia clusters have a complicated spectrum in the N–H stretching region. One antisymmetric and two symmetric stretching modes in the dimer verify an asymmetric cyclic dimer structure.1 Chlorine isotopic splittings have been resolved for the four H/D substituted (HC1)3 species, which confirm the cluster stoichiometry and triangular structure.2 The ammonia/hydrogen cyanide system reveals 1:1 and 1:2 complexes, which are identified from their FTIR spectra and characterized by comparison to similar complexes.3 The ozone/hydrogen fluoride system gives the O3–HF complex, and mixed oxygen isotopic spectra show inequivalent terminal oxygen atoms.4 The symmetrical PH3–O3 complex photolyzes to give an asymmetric HOPO2 species based on mixed isotopic spectra.5
a-Si/liquid crystal devices for compact optical neural nets
Authors: Levy James J. , Athale Ravindra A.
Published: February 2023

Optical implementations of neural net models incorporate summing and broadcasting as well as analog multiplication. Traditionally, these operations have been achieved by free space optical propagation and anamorphic optical elements (cylindrical lenses). An alternate approach uses elongated electrodes for photocurrent summation and broadcasting. Such electrooptic devices form the basis of compact optical neural net processors.1 In this paper we describe the design and fabrication of these special purpose devices and present experimental results obtained with them.
Focusing effects on the self-pulsation and oscillation in self-pumped BaTiO3
Authors: Lin J. T. , Sun Y. K. , Kim J. J.
Published: February 2023

The phenomena of self-pulsation, oscillation chaos, and frequency shift in selfpumped photorefractive BaTiO3 crystal have been recently studied.1,2 In this paper we present the pulsation and chaotic phenomena in self-pumped BaTiO3 for both divergent and convergent beams focused at various locations near the crystal surfaces. An argon laser (Innva model 70) operating at 488 nm pumps a 6- × 3- × 6-mm BaTiO3 crystal which was mounted on a translation stage to control the incident beam focusing location. The front c-face of the crystal was taken as the reference plane with the top right corner coordinate defined as (x, y) = (0,0). The convergent and divergent beams (within the crystal) are defined by focal points at (3, 6) and (3, –6) mm, respectively, where the c-axis is along the 6-mm length. A focal length f = 200 mm was used to keep the incident beam the same spot size of 1 mm on the crystal surfaces for both convergent and divergent cases.
Fast optical nonlinearity in asymmetric coupled quantum wells by inducing a static polarization
Authors: Hutchings D. C. , Wherrett B. S.
Published: February 2023

Semiconductor growth techniques, such as molecular beam epitaxy, allow the growth of 1-D potential well structures and lead to the observation of novel electronic and optoelectronic effects. In particular the confinement of electrons and holes by potential barriers leads to novel effects under application of an electric field perpendicular to the layers, such as the quantum confined Stark effect.
Practical multisegment composite-cavity semiconductor lasers
Authors: Zhang Hanyi , Chai Yanjie , Huang He , Li Haifeng , Zhou Bingkun
Published: February 2023

To provide good light sources of narrow linewidth for coherent optical communication systems we have proposed a new type of external cavity semiconductor laser with multisegment cavity structure.1 Its advantages are: (1) stable single longitudinal mode operation with high side-mode suppression ratio is easily obtained; (2) two-branch output beams standing in direction can be used. In this paper we report a practical device with multisegment cavity configuration, which basically consists of a 1.5-μm antireflection coated laser diode (LD) coupled by a graded-index (GRIN) lens to a thin Fabry-Perot etalon. The etalon is fixed on a piezoelectric transducer (PZT) and its angle of inclination can be adjusted by three fine screws for laser wavelength tuning and for optimization of alignment. The facet reflectivities of the LD, GRIN lens, and F.P. etalon are matched for achieving good single longitudinal mode oscillation. Analyses and experiments indicate that the frequency instability originates mainly from the fluctuation of the environmental temperature and mechanical disturbances in external cavity lasers.2 To reduce these effects all components are stuck on a microcrystal glass plate with low expansion coefficient and their interthermal expansions are compensated, i.e., 2αi,Li ≈ 0, where αi, and Li, are the thermal expansion coefficient and lengths of each component, respectively. The LD temperature is controlled within 0.1°C using a small Peltier cooler. All the components are put in a copper box. The device size is 32 × 26 × 65 mm3 and the actual cavity length is 2-4 cm.
Spectral and intensity noise characteristics of double external cavity semiconductor lasers
Authors: Seo D. S. , Park J. D. , Mcinerney J. G.
Published: February 2023

Double external cavity configurations are encountered in many real situations, such as coupled-cavity lasers, optical fiber transmitter modules, and optoelectronic integrated circuits. This configuration has also been found to be useful in obtaining stable single longitudinal mode operation with narrow linewidth.1 Recently, we studied the static and dynamic properties of asymmetric external cavity lasers with tilt asymmetries, whose behavior is similar to that of a double external cavity system with lengths L and 2L.2 The primary purpose of this paper is to describe extension of our previous work to more general independent double external cavity systems, for which we determine characteristics such as optical mode spectra, intensity noise spectra, and laser linewidth. The feedback phase conditions for optimum system stability and various operating regimes are determined. The most notable advantage of using a double external cavity system is that the compound cavity mode spacing can be increased by adjusting the feedback phase, while maintaining narrower spectral linewidth than that obtained using each single cavity separately. Theoretical predictions based on an effective reflectivity model with two independent feedback terms agreed well with experiments.
Inhomogeneity of Nd doped yttrium aluminum garnet
Authors: Gu Bo , Birnbaum M. , Leong B. , Bass M.
Published: February 2023

Neodymium doped yttrium aluminum garnet is the most practical and widely used rare earth doped crystalline laser crystal. Although extensive studies on this material have been carried out, there are still some interesting physical properties of this system which are not disclosed and well characterized. We studied the lifetime decay characteristic of Nd:YAG and correlated it with the inhomogeneities in the Nd-ion distribution in the sample. A 4% variation of the decay constants from point to point inside a single crystal is found and ascribed to the variation of Nd-ion concentration inside the crystal. The same setup as in Ref. 1 was used to measure the lifetimes where a small diameter (lOO-μm) pump beam excited regions that were at least 2 mm apart. The absorption of the sample in these regions was obtained at the same time by measuring the laser power before and after the sample. Since the sample ends were not antireflection coated, the Fresnel reflection of the rod ends was taken into account. The variation of the absorption coefficients from point to point in a single crystal is 25%. Since the absorption coefficient is proportional to the concentration of Nd- ions N, this observation suggests a 25% variation of N from point to point in a single Nd:YAG crystal.
Bird-wing phase conjugator with coherent beams
Authors: Dokhanian M. , Sekhar P. Chandra , George M. C. , Venkateswarlu Putcha
Published: February 2023

Ewbank reported a bird-wing phase conjugator (BWPC) with incoherent beams. We report a BWPC with two coherent beams A1 and A2 (4880 Å) incident on opposite faces of BaTiO3 at angles θ1 and θ2 with the C-axis. They individually generate self-pumped phase conjugate beams A1(t) and A2(t) detected by detectors D1 and D2. With simultaneous pumping D1 and D2 detect [A1(t) + Â2(t) - Δ1] and [A2(t) + Â1(t) - Δ2], respectively. Here Â2(t) and Â1(t) are cross couplings and Δ1 and Δ2 are mutual grating erasures. It is possible by adjusting laser beam powers and therefore self-erasures δ to have [A1(t) - δ1] and/or [A2(t) - δ2] = 0. Then under simultaneous pumping one observes only cross couplings Â1(t) and Â2(t). Keeping θ2 = 35.5° and θ1 = 60.5° and A1 = Â2 = 3 mW, one finds [A1(t) + Â2(t)- Δ1] ≃ [A2(t) + Â1(t) - Δ2] ≃ 0.Using

θ
^

1

=
43.1
°

with A1 = A2 = 3 mW, [A1(t) + Â2(t) - Δ1] ≃ 0, while [A2(t) + Â(t) - Δ2 ≃ A2(t). In general for different values of θ1, [A1(t) + Â1(t) - Δ1] and [A2(t) + Â2(t) - Δ2] are not zero and one sees clearly the BWPC.
Ring passive phase conjugator and self-pumping in barium titanate
Authors: Dokhanian M. , Sekhar P. Chandra , George M. C. , Venkateswarlu Putcha
Published: February 2023

A ring passive phase conjugator (RPPC) is formed using an electrically poled Ba- TiO3 crystal as the phase conjugator. The input is from a multilongitudinal mode argon-ion laser at 4880 A. Two auxiliary linear oscillators are supported by the RPPC. Kwong and Yariv(1) observed bistability between the two linear oscillators. But we have observed simultaneous existence of the linear oscillators supported by the RPPC. The ring itself shows large fluctuations on a very slow time scale of several minutes. There appears to be a competition between the RPPC and self-pumped phase conjugate from the crystal. If the RPPC is blocked, the self-pump grows from zero but is still weak. In the present configuration, the auxiliary linear oscillators are supported simultaneously by the RPPC, with no bistability. The signal in the linear oscillator shows large fluctuations. If the ring is blocked, the auxiliary oscillator is steady with very small fluctuations and continues to oscillate for any length of time.
Optical probing investigations using holographic gratings in LiNbO3 and GaAs and the acoustooptic interaction with surface acoustic waves
Authors: Larson D. A. , Black T. D. , Magnusson Robert
Published: February 2023

The combined interaction of a probing laser beam with traveling and stationary gratings has been studied previously in the Raman-Nath diffraction regime.1,2 This analysis was recently extended to include the interaction of diffracted orders from a surface acoustic wave (SAW) with a stationary Bragg regime grating using coupled wave analysis.2 That report demonstrated that the modulated intensity of the diffracted orders due to the interaction of the probing beam with a SAW and a Raman-Nath regime reference grating was not necessarily sinusoidal. The resulting intensity modulation for the combined interaction of the beam with a SAW and a Bragg regime reference grating was found to be purely sinusoidal. In fact, for specular and primary diffracted orders from the acoustic grating satisfying the reference grating's Bragg condition simultaneously, the intensity is modulated at the fundamental SAW frequency. This paper summarizes the essential elements of the analysis and discusses experimental configurations used to study the interaction of a probing beam with a SAW and holographic reference gratings recorded in LiNbO3 and GaAs.
Statistics of complex amplitude scattered by a rough conductor
Authors: Landsberg Yolanda , Shamir Joseph , Brunfeld Andrei , Peri David
Published: February 2023

The polarization characteristics of speckle patterns scattered from rough conductors1 are analyzed theoretically and experimentally. The analysis leads to a new measuring procedure where the complex amplitudes of the polarization components can be correlated. This procedure is substantially different from conventional methods where only intensity correlations could be measured. Unlike previously employed methods, here no a priori assumption of Gaussian distributions is necessary. Laboratory measurements performed on specially prepared samples are in excellent agreement with computer simulations and and mechanical measurements. The results of this work indicate good potential for use in noncontact evaluation of material surface quality.
Optical bistability in an improved ZnS interference filter
Authors: Sun Yin-Guan , Xiong Jun , Wang Wei-Ming
Published: February 2023

Studies have shown that the contrast of optical bistability in an interference filter with a single cavity cannot be over 4 but two cavities [sic], A higher value is reported in our experiment.
Phase-space approach to the calculation of the Rydberg constant
Authors: Rupnik Kresimir
Published: February 2023

The Rydberg constant is one of the most interesting fundamental parameters in atomic spectroscopy1 as well as in molecular spectroscopy. In molecular systems, the Rydberg transitions can be mixed with other (valence) transitions. Consequently, there is a question about the origin of the Rydberg constant in the spectroscopy of molecular systems and about the relation between the Rydberg constant and the processes of the momentum transfer from resonant electromagnetic fields. In this work, a possible phase space approach2 to the calculation of the Rydberg constant and the parameter R = 1.096834 is discussed.
Self-trapping in a weakly saturated medium
Authors: Pare C. , Gagnon L. , Belanger P.-A.
Published: February 2023

The phenomenon of self-trapping has been extensively studied in the past for both cubic and saturable nonlinearity.1 In this paper, by using a modified nonlinear Schrodinger equation, we analyze the possibility of a self-trapped beam propagating in a weakly saturated amplifying/absorb- ing medium. We consider the case of only one transverse dimension (for example, a semiconductor laser medium or a nonlinear planar waveguide structure such as the one used by Maneuf and Reynaud2 for their recent observation of spatial solitary waves). A simple exact analytical solution is obtained with a sechlike amplitude profile and a nonuniform phase front. Near this axis, this wavefront is parabolic but becomes progressively linear off-axis. Selftrapping is also predicted for a defocusing nonlinearity. The stability of the solution is investigated by using the adiabatic approximation as well as by solving the equation of propagation numerically.
Ray matrices, transfer functions, and intensities
Authors: Collins Stuart A. , Zabel Mark
Published: February 2023

We consider several topics amenable to analysis in general form by the ray matrix diffraction integral.1 The first is optical transfer functions for both coherent and incoherent light. These are defined in terms of two ray matrices, that for the optics between the input plane and the limiting aperture, and that for the limiting aperture and the output plane.
Enhanced backscatter effects of various reflectors
Authors: Welch Gisele , Phillips Ronald L.
Published: February 2023

There has been theoretical and experimental work in the area of enhanced backscatter.1,2 A simulation was developed that consists of a wave passing through a random inhomogeneous medium that has a power law spectrum. The wave is then reflected back through the same medium at which point the angular intensity statistics are studied. This simulation was tested and compared with theoretical work conducted by Jakeman.3 The cases that were studied included the diffraction effects of changing the contour of the mirror and the spectral index of the scattering medium of the phase screen. Enhanced backscatter otherwise termed as partial phase conjugation is a phenomenon that occurs when a wave has been reflected back through the same inhomogeneous medium it traversed. The concept behind this phenomenon begins when a wave passes through a random inhomogeneous medium and propagates some distance beyond the medium but within the Fresnel region at which point the wave encounters a mirror. The wave is then reflected back through the same medium. The average angular far field intensity shows this phenomenon occurring that causes an enhancement of a portion of the spatial spectrum.
Dead-time effects in curved-channel microchannel plates
Authors: Cho Doo Jin , Morris G. Michael
Published: February 2023

Dead-time effects of microchannel plates (MCPs) are due to the recharging time of the semiconducting inner wall of individual microchannels. To study the dependence of dead-time effects on the area of illumination, circular apertures of different size are imaged onto the curved-channel microchannel plate (C-MCP) using ultraviolet light (257.3 nm). It is found that an independent paralyzable counter (IPC) model, which assumes that individual microchannels of the C-MCP behave as independent paralyzable counters with a fixed dead time, agrees well with experimental results. Except for the case of a small illuminated area, the variance data as well as the mean agree well with theoretical predictions up to a certain level of illumination. However, above this level of illumination the response of C-MCP becomes highly saturated and the IPC model no longer gives good predictions. From this investigation we may conclude that the apparent coupling between microchannels observed in previous investigations1 is largely due to the complex structure of the MCP assembly, at least in the operational sense, rather than due to the intrinsic property of the MCP.
Optoelectronic real time bispectral processor for one dimensional signal analysis
Authors: Pace Phillip E. , Ramamoorthy P. A.
Published: February 2023

Multiple correlations (cumulants) and their respective frequency transformations (polyspectra) are useful in analyzing skewed and/or nonlinear random processes. In particular, the triple correlation contains more signal information than does the autocorrelation (retention of phase relations) and is finding widespread use1 in various 1-D signal processing applications such as ultrashort laser pulse reconstruction, detection of phase coupling, and nonlinear spectroscopy. One of the main drawbacks, however, is the computational complexity that is associated with the cumulant generation. In this paper we present an optoelectronic parallel processor for the real time computation of a 1-D signal's bispectrum. Due to the parallel nature of the architecture, the new bispectral processor eliminates the serial scan necessary to retrieve the third-order cumulants. In addition, since the cumulant generating architecture has no moving parts, the usual instrument aberrations inherent in the free-space triple-intensity interferometer are reduced and the SNR efficiency is increased. We demonstrate how this optical bispectral processor can be integrated with digital electronics for the real time digitization of a 1-D signal's bispectrum.