bluuebunny/crossref_metadata_2025 huggingface dataset:
Inexpensive, compact electron gun for laser applications
Authors: Bayless John R.
Published: February 2023

Large-area electron guns are critical components in many high-energy gas laser systems. The secondary emission electron (SEE) gun, in which a beam is generated by ion bombardment of the cathode, offers an attractive option for pulsed laser applications. With this type of cold cathode gun, a dc voltage is applied to the cathode and the electron beam is controlled by modulating the source of ions in which resides a ground potential. This design greatly simplifies the electron gun power system. A SEE gun system has recently been developed which provides a 150-kV, 5- × 150-cm2 beam at current densities of up to 12 mA/cm2 (uniformity about ±10%) in 30-µs pulses at 30 pps. It is expected that the SEE gun can be easily scaled to beam voltages of >300 kV, beam areas >10,000 cm2, peak current densities exceeding 1 A /cm2, time-averaged current densities >0.5 mA/cm2, pulse lengths of 0.1 µs to dc, and pulse repetition rates >1 kHz with good uniformity (±5%), high reliability, and long life (>1000 h). Furthermore, the inherent simplicity of the SEE gun results in low cost and a compact, lightweight system.
Color-selective self-pumping of multicolor beams in barium titanate
Authors: Sekhar P. Chandra , Dokhanian M. , Venkateswarlu Putcha , George M. C.
Published: February 2023

Phase conjugation of multicolor beams has been reported by others.1 Here we report color-selective self-pumping when a multicolor beam from an argon-ion laser with an all-line mirror is incident on an electrically poled barium titanate crystal. If the intensity of the incident beam A1 < 25 mW, the self-pump A1 is blue (4880 Å). If the intensity is increased beyond 25 mW, A1 changes from blue to green slowly (approximately several seconds) with both blue and green seen for a short time, after which the blue signal decays to zero. A second multicolor beam A2 (30 mW), crossing A1 in the crystal and individually (without A1) self-pumping in the green, can control the color of A1. If initially A1 is blue, and A2 is put on, A2 also self-pumps but in blue. A1, along with A2, gradually changes to green, with both of them showing both blue and green for a few seconds.
Bragg gratings in photopolymer buried-channel waveguides
Authors: Steijn Kirk W. , Marchegiano Joseph E. , Booth Bruce L.
Published: February 2023

Grating structures will be key elements of high density wavelength division multiplexed (WDM) communications systems. A recently developed acrylate photopolymer waveguide technology, referred to as Polyguide,1,2 has the ability to combine in a single material system both high quality single-mode waveguides3 and thick Bragg grating structures.4 We have investigated the performance of microgratings in buried single-mode guides for WDM applications in this polymer system. Gratings are created holographically using an argon-ion laser, with size and position determined by a photolithographic mask. Grating lengths of 25-250 µm have been fabricated in a variety of device structures.
Irreversible photoinduced bleaching in poly-4BCMU
Authors: Rochford K. , Gong Q. , Torruellas W. , Zanoni R. , Stegeman George I.
Published: February 2023

Poly-4BCMU is a soluble polydiacetylene which has a large nonresonant third-order nonlinearity. The solubility of poly-4BCMU makes this an attractive nonlinear material for fabricating nonlinear integrated optical devices for high speed communications. In this paper we report results which show that poly-4BCMU bleaches in open air when exposed to radiation within the absorption band. Furthermore, the material can be bleached by two-photon absorption. The bleaching can be stabilized by removal of the oxygen. This effect is shown to be useful for fabricating integrated optical structures such as channels and gratings. Nonlinear measurements of the bleached and unbleached material are reported as well.
Poling and implantation cladding of a-axis LiNbO3, fibers
Authors: Saini D. P. S. , Chang R. S. F. , Djeu N.
Published: February 2023

Single crystal materials in fiber form can potentially lead to highly efficient nonlinear optical devices at low power levels. The possibility of producing high quality crystal fibers by the laser heated miniature pedestal growth technique has previously been demonstrated.1 The full exploitation of such fibers would require the development of suitable procedures for their poling and cladding, which are essential for phase matching and core reduction purposes. We have used the same miniature pedestal growth technique to grow a-axis LiNbO3 fibers with cross-sectional dimensions of a few tens of microns. These fibers were subsequently poled by a simple procedure which preserved their smooth surface morphology. The single domain fibers prepared this way were then clad through multiple energy implantation with He ions starting at 5 MeV in decreasing steps.
Quantitative estimation of Raman scattering effects on the submarine light field
Authors: Stavn Robert H. , Weidemann Alan D.
Published: February 2023

Recent optical probes of clear ocean waters conducted by the Naval Ocean Research and Development Activity and others have indicated that the submarine light field of clear ocean waters at longer visible wavelengths (520 nm +) is comosed of both solar photons and photons ascribable to water Raman emission. The Raman scattering of shorter wavelength photons in the visible waveband shows up most strongly at the longer wavelengths where solar photons are heavily absorbed. The ability to predict the propagation and fate of solar photons requires a knowledge of the water Raman scattering process in ocean waters. We have combined results from a Monte Carlo simulation of light propagation in the sea incorporating water Raman scattering with data collected by NORDA in the Sargasso Sea to make quantitative estimates of the percentage of photons at any given point in the marine hydrosol that are due to water Raman emission. The required measurements are the apparent absorption coefficient of the hydrosol calculated from the measured irradiance field and the true Lambert-Beer absorption coefficient measured directly from the hydrosol. By this method the variability of water Raman emission at a given wavelength due to removal of photons by components other than molecular water can be accounted for. The average cosine parameters of the mean photon paths have also proved to be sensitive indicators of the interaction of water Raman photons and the various scattering components of the marine hydrosol.
Spectral reflectance of the ocean from CZCS
Authors: Gordon Howard R.
Published: February 2023

After atmospheric correction, the Coastal Zone Color Scanner (CZCS) on Nimbus-7 provides the oceanic normalized waterleaving radiance1 L at wavelengths of 443, 520, and 550 nm. From L, the standard CZCS biooptic algorithm for Case 1 waters can be used to estimate the phytoplankton pigment concentration C. The problem examined here is how to utilize these data to estimate L across the visible spectrum. The approach taken is to combine the CZCS-derived L values at 520 and 550 nm and C with the semianalytic model of ocean color derived by Gordon et al.
1
to estimate the scattering coefficient of the particles (plankton plus detrital material). The model is then applied to other wavelengths over the 370-595-nm spectral range and compared to Clark's2 in-water radiance measurements. The results suggest that in Case 1 waters, L can be estimated over this range from measurements at the three CZCS wavelengths with an accuracy of 10-15%.
Two- and three-grating resonators for multiatmosphere CO2 TE lasers
Authors: Izatt Jerald R. , Rob Mohammad A. , Zhu Wen-Sen
Published: February 2023

The multiatmosphere CO2 TE laser provides broad continuous turnability in the 9-11-µm region which is useful in many spectroscopic and optical pumping applications. In a single-grating laser, the linewidth is typically greater than 3.5 gHz, and it is often necessary to restrict the output power to avoid damage to intracavity optical elements. Both of these factors compromise the usefulness of the CO2 TE laser. The linewidth can be substantially reduced by using two or more gratings in the cavity. Introduction of a third (partially reflecting) mirror between the gain section and the gratings enhances the line narrowing and also helps to protect the gratings from power damage. We have analyzed several alternative multigrating resonator configurations. Using the optimum double-grating configuration resulting from this analysis, the linewidth was measured with a wedged etalon and a 128-element array of pyroelectric detectors. The result for a 10-atm laser was 600 MHz. When used with a 125-cm long, 1-atm CO2 TEA laser, the same grating combination produced consistent SLM operation.
Iterative correction process for optical thin film synthesis with the Fourier transform method
Authors: Verly P. G. , Dobrowolski J. A.
Published: February 2023

Inhomogeneous films are difficult to produce, but they have potentially a number of advantages over the more classical coatings composed of multiple homogeneous layers. One of the few approaches available for the synthesis of such films is the Fourier transform method. It is fast and it can also yield homogeneous multilayers. Essentially, it is based on a Fourier transform relationship between the logarithmic derivatives 1/n dn/ dx of the refractive index profile, and a spectral function Q(σ) which depends on the desired spectral performance. A proper definition of Q(σ) is essential for accuracy. The analytical forms of Q(σ) proposed in the past are approximate, especially when the desired reflectance is high.1 Sossi proposed an interesting approach where successive corrections ΔQ(σ) are added to Q(σ). A modified version, developed and programmed at the NRCC, is described. Examples illustrate the influence of several key parameters not addressed before and which have important practical implications. In particular, we show that the thickness of the films can be reduced considerably by defining appropriately the complex phase of Q(σ). This phase can also be used to modify the shape of the refractive index variations, without affecting the spectral performance.
Bare and thin film-coated substrates with maximally flat reflectance vs angle of incidence curve for incident unpolarized light
Authors: Azzam R. M. A. , Alnajjar Abdalla M.
Published: February 2023

For any optically isotropic bare or coated substrate the power reflectance R
v
(ϕ) is an even function, R
v
(–ϕ) = R
v
(ϕ), of the angle of incidence ϕ, hence all the odd-numbered derivatives

R
v

(
n
)

=
 

d
n

R
v

/

d
ϕ
n

are identically 0 at ϕ = 0, independent of the incident polarization v. For a bare substrate and incident unpolarized light (v = u), the second derivative

R
u

(
2
)

also, so that the flatness of the R
u
vs ϕ curve, from ϕ = 0 up to a large angle (>45°) is determined by the fourth derivative

R
u

(
4
)

. The condition that

R
u

(
4
)

=
0

gives the maximally flat response (MFR) and leads to a specific constraint between the real and imaginary parts, ϵ
r
and ϵ
i
, of the substrate complex dielectric function ϵ. This constraint is determined and the corresponding complex plane locus is presented. Examples of specific substrates with the MFR at specific wavelengths are given. Subsequently, the case of an arbitrary absorbing substrate which is coated by a transparent thin film is considered. The refractive index and thickness of the film that null

R
u

(
2
)

and

R
u

(
4
)

simultaneously are determined to achieve the MFR by the film-substrate system at a given wavelength.
Nonsaturable absorption due to stimulated emission of radiation
Authors: Hong C. K. , Nathel H. , Minich R. W. , Garrison J. C. , Ritchie B.
Published: February 2023

We report an observation of nonsaturable absorption of light. When a laser medium in a small aspect ratio geometry is uniformly and transversely pumped, amplified spontaneous emission (ASE) builds up along the longitudinal axis. The higher ASE intensity at the ends of the cell repopulates the ground state through the stimulated emission process more rapidly than at the center of the cell. Therefore, the absorption of the pump light is enhanced at the ends and the transmitted pump beam shows a nonuniform profile with a peak at the center. When the occupation of the states other than the upper lasing state and the ground state can be ignored, the normalized profile of the transmitted pump beam becomes identical to that of the fluorescence depicting the upper state population distribution. This fact has been confirmed experimentally with a R6G dye cell pumped with various intensities of frequency doubled Nd:YAG laser (λ = 532 nm, 10-ns pulse duration). The percentage of the absorbed pump energy at the ends of the cell remains the same, virtually nonsaturable, whereas at the center it decreases as the pump intensity increases.
Neuromechanisms of visual perception and attention in monkeys
Authors: Desimone Robert
Published: February 2023

In spite of the fact that the computing architecture of the brain is massively parallel, our ability to process incoming sensory information in parallel is surprisingly limited. It is not possible, for example, to recognize within the same instant more than one or two objects in a crowded scene. Thus, much of the information impinging on the retina must be filtered out centrally, a process usually termed attention. To understand how this comes about, we have recorded from neurons in visual areas of monkey extrastriate cortex known to underlie object recognition. We have found that selective attention serves to remove irrelevant information from the receptive fields of extrastriate neurons and sharpen their selectivity for visual features such as orientation or color. These effects of attention may explain both why we have little awareness of unattended stimuli, and why our resolution of spatial location and visual features is improved inside the focus of attention. Our behavioral studies in monkeys suggest that attention controls visual processing via signals from the lateral pulvinar nucleus of the thalamus.
Phase-shifting fringe-projection profile accuracy
Authors: Brophy Chris P.
Published: February 2023

The performance of a commercial optical contouring system is presented. The AMMON 2000, an optical casting system that is used to contour the bottom of the human foot for the podiatry industry, incorporates a phase-shifting fringe-projection profiler. The height profile data, z(x, y), measured with the instrument, are used to automatically design and surface a correcting orthotic. Data reduction software accounts for geometric distortions that are intrinsic to fringe projection topography when generated with a nontelecentric optical system. Contributions to the distortion that are due to the finite distance of the camera and projector exit pupils are detailed. By knowing the various parameters associated with the optical setup, as well as the position of a single reference point on the object, found by some other means, it is theoretically possible to transform the raw OPD data to the desired height contour, z(x, y), with absolute accuracy. In the AMMON 2000 the reference point is obtained by viewing the object at an angle that is nearly orthogonal to the projection axis.
Operator techniques applied to the driven harmonic oscillator
Authors: Croxson Paul
Published: February 2023

For many problems a solution in the Heisenberg picture is straightforward, but the Schrodinger picture solution is difficult, although presumably it is possible. A good example is the driven harmonic oscillator. The equations of motion are easy to solve when the driving force is periodic. The Hamiltonian can be reduced to time-independent form and the evolution operator is easy to write down as a single exponential. To work out the transition probability from one number state to another, it is necessary to decompose the exponential. As well as the Baker-Hausdorff formula, other operator techniques are used together with the coherent-state projection operator, to solve the problem.
Acoustically tuned integrated optical filters
Authors: Smith D. A. , Cheung K. W. , Baran J. E. , Johnson J. J.
Published: February 2023

The acoustically tunable optical filter is a peerless candidate for very broad tuning range, nanometer bandwidth optical filtering applications, including switching and filtering for WDM networks, and optical spectrum analysis. Only recently has the unique capability of the acoustooptic filter to independently switch many different channels been exploited, since integrated optics has been required to reduce power consumption to manageable levels.
Nonlinear facilitation of spatial masking by orthogonal gratings
Authors: Wilson Hugh R. , Ferrera Vincent P.
Published: February 2023

Masking studies employing cosine gratings have been used previously to measure both the spatial frequency and orientation tuning of spatial mechanisms in human vision. Here we report a powerful nonlinearity whereby a grating orthogonal to the test greatly enhances the masking produced by gratings at other orientations. Thus, a horizontal cosine grating added to a 45° grating, each at 25% contrast, causes a threshold elevation in a vertical test grating approximately three times greater than that produced by doubling the contrast of the 45° grating alone. Similar increases in masking were also observed when a grating orthogonal to the test was added to a mask component at either 22.5° or 67.5°. This orthogonal enhancement of masking is reduced or absent when mask and test differ in spatial frequency by a factor of 3 or more. Finally, orthogonal masking enhancement disappears when the test is flashed 250 ms after the onset of the mask. These results may reflect the operation of a nonlinear feedback mechanism that pools responses of orientation selective units and functions as a contrast gain control.
Phase conjugate oscillators
Authors: Lee Wun-Shung , Chi Sien , Yeh Pochi , Saxena Ragini
Published: February 2023

Optical resonators containing a phase conjugate mirror (PCM) have been a subject of great interest, where the PCM is employed as an end mirror of the resonator cavity for intracavity aberration correction.1 Recent theoretical analysis indicates that the insertion of a PCM inside a ring laser cavity results in a reduction of the lock-in threshold and reduces the imbalance between the amplitudes of the oppositely directed traveling waves.2 In the extreme case of phase conjugate oscillation without conventional gain, lock-in can be completely eliminated.3 We have developed a general theory for nondegenerate oscillations in a phase conjugate oscillator (PCO) i.e., an optical resonator with a PCM as an intracavity element. The PCM consists of a nonlinear transparent medium pumped by a pair of counterpropagating laser beams so that phase conjugation of an input beam with possible gain is achieved by nondegenerate four-wave mixing (NFWM). The linear absorption/gain in the medium is also taken into account. In the absence of any conventional mirrors so that the PCO behaves like an ordinary PCM, we recover the results of phase conjugation by NFWM.4 Our study shows that the nonlinear gain required for oscillation is considerably increased/decreased due to the linear absorption/gain in the medium, while the bandwidth and the sidelobe structure of the bandpass filter are also affected. In the case when there is only one conventional mirror, the PCO reduces to a phase conjugate resonator (a resonator bounded by a conventional mirror and a PCM). Our theory shows that nondegenerate oscillation is possible in such a resonator. The theory can also be used to study the effects of linear absorption/gain on the filter operation.
Studies on the transient buildup of a photorefractive double phase conjugate mirror
Authors: He Qi-Chi , Sung Chi C. , Duthie J. Graeme
Published: February 2023

In the application of a photorefractive double phase conjugate mirror, the transient buildup and the dynamic behavior are both interesting and important. The temporal instabilities of the driven DPCM were studied recently.1 In this work we present a numerical study of the transient buildup as a function of various parameters: total intensity, beam ratio, steady state photorefractive coupling gain, and seeding levels. We take the standard four-wave mixing model2 including the Debye relaxation equation for the space-charge electric field, using the typical boundary condition for the DPCM and no initial space-charge field. We find that (1) the buildup time of the DPCM, which is defined as the time the phase conjugate reflectivity reaches 90% of its steady state reflectivity, is also inverse proportional to the total intensity, (2) the buildup time decreases and tends to saturate as the steady state coupling gain increases, (3) the buildup time increases approximately quadratically as incident beam ratio deviates unity.
Optical finishing of nonlinear crystals by single point diamond turning
Authors: Fuchs Baruch A. , Syn Chol , Velsko Stephan P.
Published: February 2023

We have demonstrated that diamond turning can produce λ/10 surface with a residual roughness of <50 Å in soft, organic nonlinear crystals such as L-arginine phosphate (LAP) and urea. Recent damage testing of diamond turned LAP plates showed that the damage threshold was as high as 50 J/cm2 for 10-ns pulses at 1.06-μm wave length. We have also developed diamond turning methods for hard, high temperature materials such as lithium niobate and barium metaborate. Polished lithium niobate exhibits laser-induced surface damage at extremely low fluences—<5 J/cm2 for 10-ns pulses at 1.06 μm. We have identified diamond machining conditions in which lithium niobate exhibits ductilemode cutting, with residual surface roughness of <20 Å in 2- × 2-cm2 pieces. This roughness is more than an order of magnitude lower than previously reported results with this crystal. However, some tool wear and built-up edge formation on the tool cutting edge has been observed. We have studied the effect of cutting orientation, rake angle, and cutting fluid on tool wear and surface quality.
z-scan: a simple sensitive technique for measuring refractive nonlinearities
Authors: Said A. A. , Sheik-Bahae M. , Wei T. H. , Young J. , Hagan D. J. , Soileau M. J. , Van Stryland E. W.
Published: February 2023

We present a simple yet highly sensitive technique for determining the sign and magnitude of nonlinear refraction. Using a single focused Gaussian beam with a constant input pulse energy, the far field transmittance is measured through a finite aperture as a function of the sample position with respect to the focal plane along the propagation path (z). The result is a dispersion-shaped curve with a maximum (peak) and a minimum (valley) corresponding to the far field beam narrowing or broadening, respectively. The ∓ sign of the nonlinear refraction is immediately deduced from a z-scan depending on whether a peak occurs before (−z) or after the focus (+z), respectively. The magnitude of the refractive nonlinearity is easily obtained from a simple linear relation between the normalized peak-to-valley transmittance change (ΔTp−v) and the on-axis nonlinear phase shift at the focus (ΔΦ0): This relation was obtained by using a simple wave optics formalism. We have employed this technique to investigate the nonlinear refraction in various types of material such as semiconductors (InSb, ZnSe, CdTe), glasses (BaF2, MgF2), semiconductor doped glasses and liquids (CS2) at various laser wavelengths. A phase distortion resolution of ≃λ/300 was obtained in n2 measurements of BaF2 at 532 nm.
Amplitude modulated phase-only filter
Authors: Awwal Abdul Ahad S. , Karim Mohammad A. , Jahan Syeda R.
Published: February 2023

Amplitude information, if properly incorporated along with the phase, can be utilized to improve the discrimination efficiency. In this work, we introduce a novel amplitude modulated phase-only filter (AMPOF) that effectively utilizes both amplitude and phase information and, at the same time, avoids the operational difficulty of the inverse filters. To counter excessive energy absorption and, at the same time, to achieve a significantly uniform filter plane spectrum, one can formulate an AMPOF characterized by D{exp[−jϕ(u, v)]}/[|F(u, v)| + a], where 0 < D ⩽ 1 and a> D, and F(u, v) is the object spectrum with phase ϕ(u, v). Parameter a is useful in (i) overcoming the indeterminate condition, (ii) ensuring that the gain is less than unity, and (iii) suppressing noise or bandlimit the filter or both. To discriminate between the object and the filter, the correlation peak energy is normalized with respect to the total output energy. An AMPOF based correlator produces autocorrelation peaks, narrower as well as larger than those of the POF based correlator. Furthermore, it provides a larger value for the ratio of auto- and crosscorrelation powers. A computer-controlled LCTV and MOSLM can be used to store the appropriate filter. A binary AMPOF amplitude mask can be designed using a scheme1 used for fabricating a binary inverse Gaussian filter.
Optical analysis of two types of grazing incidence ring resonators for free-electron lasers operating in the extreme ultraviolet
Authors: Gabardi David R. , Shealy David L.
Published: February 2023

Due to the poor reflectivity of mirrors in the extreme ultraviolet when used at normal incidence, it has been suggested that resonators for free-electron lasers operating in this wavelength region employ grazing incidence mirrors in ring type configurations.1 An algorithm using Gaussian beam propagation rules has been used to determine the cavity parameters for two types of such a resonator. Both types of resonator incorporate four off-axis conic mirrors into their designs to provide the desired degree of beam expansion and focusing as well as a number of flat mirrors to assure that appropriate grazing angles of incidence are maintained. As the beam travels around these cavities, it is passed though a focus in one design type while in the other it remains collimated. Both design types support Gaussian TEMoo mode propagation. The two cavity designs have been analyzed in vacuum conditions; that is, without the wiggler gain interaction, using a diffraction-based computer simulation code and with a paraxial ray trace treatment of their thin lens analogs. Cavity stability as it relates to the degree of beam expansion, laser wavelength, and choice of resonator design type is discussed.
Nonlinear magnetooptics of vacuum: second harmonic generation
Authors: Ding Y. J. , Kaplan A. E.
Published: February 2023

Photon-photon scattering in vacuum1 is perhaps one of the most fundamental mechanisms which can give rise to nonlinear optical effects.2 Here, we demonstrate the feasibility of new nonlinear magnetooptic effects in vacuum giving rise to optical second harmonic (SH) generation of the fundamental wave under the action of both strong dc magnetic field H0 and optical laser radiation. The strongest interaction between the fundamental wave and SH occurs when both of them propagate along the direction normal to H0. In the case of an elliptically polarized wave with the ratio between amplitudes of two decomposed components along H0 and the direction normal to it being 2/√7 ≃ 0.76, SH is linearly polarized. In the case of a linearly polarized wave, SH is also linearly polarized. The ratio of maximal intensity of SH (which occurs at the polarization angle of the fundamental wave with respect to H0, θ1 = 0°) to minimal intensity (which occurs at θ1= 90°) is equal to (7/4)2 ≃ 3. A minimal angle between the polarization of SH and H0 is (θ2)min ≃ 74° and θ1 ≃ 53°. In the case of a circularly polarized wave, SH is still circularly polarized with the same rotation as the fundamental wave. The ratio of maximal intensity of SH for linear polarization to that for circular polarization is

(
7

2

/
3
)

2

≃
10.9

. Assuming H0 ~ 105 G, interaction length ~ 50 cm, radiation wavelength ~ 1 µm (Nd:glass laser), pulse duration ~10−9 s, and the laser focal area ~2.5 × 10−3 cm2, we estimate that the intensity ~4.1 × 1017 W/cm2 is required to observe 30 averaged photons for a single pulse at SH frequency (wavelength ~ 0.5 µm) for the parallel polarization (θ1 = 0°, θ2 = 90°) and ~10 averaged photons for the normal polarization (θ1 = θ2 = 90°). An even lower number of photons per pulse can be used if the averaging over a large number of pulses is used; e.g., at a 10-Hz repetition rate, only laser intensity ~2.2 × 1015 W/cm2 is required to observe 30 averaged photons within an hour.
Second harmonic generation as a probe of free volume and local constraints on polar groups in polymers
Authors: Boyd Gary T. , Francis Cecil V. , Trend John E.
Published: February 2023

Poled polymers are of interest as new electrooptic materials. In situ second harmonic generation (SHG) provides an important tool for studying and optimizing the processing of these polymers. Here, SHG is used to probe the extent of electric field-induced orientation of dopant chromophores in polymethyl methacrylate and polycarbonate. The results indicate that a fraction of the dopants were able to freely rotate at room temperature both before and after thermal cycling. This fraction correlates with the dopant molecular volume, and the long term decay time of the SHG signal after poling. The SHG signal gradually increases as the temperature is raised above an onset temperature far below the glass transition temperature of the host polymer.
Rigorous analysis of scattering from a strip grating twist reflector
Authors: Sohail S. , Naqvi H. , Gallagher Neal C.
Published: February 2023

Periodic metallic grating structures, with periods of the order of the wavelength of the incident electromagnetic field, influence both the phase and polarization of the reflected field. A convenient decomposition of the polarization is into fast and slow polarized modes, where the magnetic or electric field component parallel to the grating direction, respectively, is zero. In the case of a corrugated surface twist reflector, Kok and Gallagher,1 derived the optimum height required for various angles of incidence in order for the reflected fast and slow polarized modes to be in phase. In practice twist reflectors are also constructed by placing wires or strip gratings on a dielectric slab of some thickness w, backed by a conducting ground plane. Recently we presented a rigorous analysis of scattering from a strip grating. We extend our solution procedure to be applicable to the analysis of scattering from a strip grating twist reflector. It is shown that completely erroneous results are obtained if an approximate procedure is used. We compare the operation of the strip grating twist reflector to the corrugated surface twist reflector and show that the two behave similarly if air is used as the dielectric for the strip grating twist reflectors.
Design and performance of layered synthetic microstructures on diffraction gratings in the VUV
Authors: Hunter W. R. , Rife J. C. , Cruddace R. G. , Barbee T. W.
Published: February 2023

The success of layered synthetic microstructures (LSM) as reflectance enhancing coatings for mirrors at wavelengths <300 A has prompted a study of their properties when applied to diffraction gratings. In designing the coating, its interference order, usually the first order, must be paired with a suitable diffraction order of the grating. In addition a compromise must be made to reduce the incompatibility caused by the simple Bragg law performance of the grating with the corrected Bragg law performance of the coating.
Visual process in retinal photoreceptors: analysis by intrinsic light scattering signals
Authors: Hofmann Klaus P.
Published: February 2023

The rod photoreceptor of the retina is a quantum detector whose physiological function in physically unfavorable conditions (body temperature, salt solution) is made possible by specific protein interactions. Photon energy is stored by the receptor protein rhodopsin (R) in a structurally transformed state. Activated R interacts with transducin (a G-protein or guanine nucleotide binding protein). This catalyses binding to G of energy-rich nucleotide which in turn releases G in an activated form. Absorption of one photon leads to the activation of 1000 G in 1 s. Analogous relay systems are found from bacteria to man. Intrinsic physical properties of the rhodopsin G-protein system allow photometric studies in situ and in real time. Activation of R and interaction with G are measurable by absorption spectrophotometry. Activation of G is measurable by light scattering (LS) changes (signals) arising from the shift of the G-protein mass during activation. A continuous transretinal, near infrared LS probing beam affords direct monitoring of G-activation induced by visual stimuli. These optical techniques, combined with biochemical and physiological approaches, have been used to study the sites of R-G interaction and the thermodynamics of the G-relay in situ. G-activation is not modulated by previous illumination, indicating a remarkable constancy of the R-G amplification step in the visual transduction pathway.
Cotangent states of the electromagnetic field
Authors: Slosser John J. , Meystre P.
Published: February 2023

We consider a simple quantized harmonic oscillator driven by a current of spin 1/2 particles resonant with the oscillator frequency. A possible realization of this model might be achieved in a micromaser. Our analysis shows that the system may evolve to pure states j of the field even for mixed state initial conditions. Specifically, writing the field state as |f⟩ = Σ
n
|n⟩ we find the two possible solutions: For this reason we call these states cotangent and tangent states of the harmonic oscillator, respectively.
Diffraction effects due to an occulting aperture: comparison of theories
Authors: Scholl Marija S. , Wang Yaujen
Published: February 2023

Traditionally, the Fraunhofer diffraction formulation has been considered to be an adequate approximation for the calculation of light distribution in the diffraction plane for most purposes. It has proved effective in the system design and those scientific applications where the intensities of two sources differ by up to a few orders of magnitude. Due to continued interest in detecting dim objects in the neighborhood of bright objects, a more nearly exact formulation of diffraction theory is needed to calculate the distribution of the diffracted light in the focal plane when the intensity ratio between the dim object and the bright object approaches 10 exp(−8). This is the case when an extrasolar planet is searched for in the presence of its star. The vector diffraction theory, geometrical diffraction theory, and Fraunhofer diffraction formulations are compared for their applicability to solving simultaneously two diffraction problems with intensity ratios of incident illumination varying from 10 exp(−3) to 10 exp(−8).
Quality of the Fourier transform produced by an imaging lens
Authors: Walther A.
Published: February 2023

Many users of coherent imaging techniques would be delighted with a lens that produces not only a high quality Fourier transform but also a high resolution image of a specified object plane. Unfortunately there is a theorem in geometrical optics that prohibits the design of lens systems that can perform both these tasks flawlessly. To shed some light on the nature of this limitation several proofs of this theorem are presented. One of these proofs, based on a straightforward application of the wave equation without any reference to geometrical optics, shows clearly that this design restriction has a firm foundation in the basic laws of physics.
Coherent state superpositions in the degenerate parametric oscillator
Authors: Carmichael H. J. , Wolinsky M.
Published: February 2023

The degenerate parametric oscillator is an important source of squeezed light. If the pump mode is adiabatically eliminated, its operation is governed by two dimensionless parameters: the pump parameter λ and the coupling constant g. The pump parameter controls the threshold behavior predicted by semiclassical theory (threshold is reached for λ = 1). The coupling constant g determines the strength of the quantum fluctuations. The optical parametric oscillators used to generate squeezed light have g ~ 10–4 ≪ 1.1 Therefore, in these systems the quantum fluctuations only produce very small perturbations about semiclassical states. We have recently shown how the steady state of the degenerate parameter oscillator changes as a function of coupling strength.2 In the strong coupling limit, major departures from semiclassical states occur; for g2 ≫ 1 and 2λ2/g2 ≪ 1 the steady state approches the coherent state superposition

|

ψ
+

〉
=
|

λ
/
g

〉
+
|
−

λ
/
g

.
Quantum effects in optical interference
Authors: Mandel L. , Ou Z. Y.
Published: February 2023

A number of unusual optical interference effects have been observed that involve pairs of photons and cannot be understood or described in terms of classical electromagnetic waves. They include fourth-order interference of >50% visibility, which is unchanged when one of the beams is attenuated tenfold; measurement of the time interval between two photons with femtosecond accuracy; demonstration of phase memory in the two-photon down-conversion process due to vacuum entanglement.
Optical implementation and analysis of a two-layer heteroassociative memory
Authors: Hsu Ken , Li Hsin-Yu , Psaltis Demetri
Published: February 2023

We describe the implementation of a holographic heteroassociative memory and the modeling of the nonlinear dynamics of the system. The system uses thermoplastic plates for storing associative images and a Hughes liquid crystal light valve (LCLV) for image amplification and thresholding. Planar holographic interconnections are used for interconnecting patterns from one layer to another. The problem of degenerate readouts in planar holographic interconnections is analyzed and the technique of using sampling grids for specifying unique interconnections is described. The optical system is arranged as a feedback loop. It locks the recognized input and its associative image as a stable state in the loop. We show that the main factors determining the dynamics of the system are the optical gain and the similarity between input and the stored images. The optical system is equivalent to a two-layer network with feedback. Equations describing the dynamics of the system are derived, including the effects of the square-law detection by the neural plane. A geometric method is introduced which allows us to analyze how the system state evolves and how the parameters influence the evolution.
Some exact solutions in self-focusing
Authors: Gagnon L.
Published: February 2023

It is well known that self-focusing and self-(de)focusing theories are described by the (2 + 1)-dimensional nonlinear Schrodinger equation iuz + us1a1 + us2s2 = a1u|u|2, where u(z, S1, S2) is the slowly varying field amplitude, z is the propagation coordinate, a1 is a constant, and S1 and S2 are proportional to transverse coordinates. (A similar equation stands for the dispersive self-modulation of waves including one transverse dimension.) Since not integrable, one cannot use the inverse scattering method to solve it. However, particular solutions can be obtained on the basis of symmetry arguments. In fact, one observes that the equation is invariant under translations of coordinates, rotation in the (S1, S2)-plane, constant change of phase, simultaneous dilation of coordinates, Galilean boosts and Talanov's lens transformation.1 By appropriate combinations of these symmetries, one can find an optimal set of invariant quantities that can be used to reduce it to ordinary differential equations. These equations are finally solved, for particular parameter values, by identification to Pain-leve type equations. The norm of the solutions are all expressed in terms of elliptic functions of the variables

p
2

=

S
1
2

+

S
2
2

or tanθ = S1/S2. Their diagram representations show similar behavior with solutions obtained from numerical analysis.2
CO2 laser frequency stabilization using rf optogalvanic Lamb dip
Authors: Shy Jow-Tsong , Tsai Chin-Chun , Lin Tyson , Shieh Chern-Yn , Yen Tsu-Chiang
Published: February 2023

Recently, Shy and Yen1,2 stabilized a CO2 laser at the Lamb dip using the optogalvanic signal in a dc glow discharge of low pressure N2-CO2 gas mixture. This method can be applied to regular, sequence- and hot-band laser transitions. However, it has several difficulties, e.g., it is not easy to have stable discharge at a pressure <500 mTorr and the signal-to-noise ratio (SNR) is strongly dependent on the conditions of cathode. In this paper, we present our results on the optogalvanic Lamb dip frequency stabilization of a CO2 laser using rf discharge. The experiments were carried out in a weak rf glow discharge driven by a Colpitts oscillator.3 The gas mixture (1:1 CO2-N2) slowly flowed through the cell at a pressure from 100 to 300 mTorr. The cell was outside the CO2 laser cavity. The Lamb dip signal was used to lock a waveguide CO2 laser with a frequency stability better than 1 × 109.
Scattering from slightly rough random surfaces
Authors: Nieto-Vesperinas M. , Soto-Crespo J. M.
Published: February 2023

In this paper we study the validity of the small perturbation method for 1-D perfectly conductive random rough surfaces. We have obtained an expression for the diffuse component of the mean scattered intensity up to fourth order in powers of k0σ for S- waves (k0 = 2π/λ, a is the rms height). For P-waves it is not possible to obtain the fourth-order term. The perturbative expressions are derived from the Rayleigh hypothesis and also from the extinction theorem. In both cases the final expressions for the mean diffuse intensity are the same. Comparisons with exact numerical results and with those predicted by the Kirchhoff approximation are made. This permits us to establish some criteria on the validity of the perturbative solution, obtaining some new interesting facts. In particular, we show that the total incoherently scattered energy is the parameter that basically determines the applicability of the perturbative solution. Precise curves marking the zones of validity of the second-order perturbative intensity are drawn. Simultaneously, the shape of the diffuse halo as a function of the correlation length T, the angle of incidence θ0, and the polarization is studied at small k0σ.
Observation of exciton linewidth narrowing in thin barrier GaAs/AlxGa1-x As superlattices
Authors: Jacob J. M. , Hwang S. J. , Jung P. S. , Song J. J. , Tu C. W. , Vree-Land T.
Published: February 2023

A variety of optoelectronic devices utilize the unique properties of excitons in quantum well structures. Exciton linewidths are important design parameters in optimizing performance of certain devices. We have investigated exciton linewidths in a series of high quality MBE GaAs/(Al,Ga)As superlattice samples. The well widths and the aluminum concentrations in the barrier layers were fixed while the barrier layer thicknesses were varied. The samples were designed to have low potential barrier heights and substantial subband dispersion. The superlattice layer widths were accurately determined by cross-sectional transmission electron microscopy. The exciton peak widths were measured by excitation spectroscopy performed at 15 K. We have found that both the heavy hole and light hole excitonic peak widths decrease as the barrier width decreases. Significant narrowing was observed between the thick barrier quantum well-like samples and thin barrier superlattices with substantial well couplings.
Effects of blur on separation discrimination
Authors: Geisler Wilson S.
Published: February 2023

Optical blur has a wide range of effects on localization performance, depending on stimulus configuration and task. Furthermore, in some tasks, the efficiency of human observers, relative to an appropriate ideal observer, actually increases with increasing blur.1 To explore this puzzle, separation discrimination was measured for 5'-long line segments as a function of base separation, luminance, and level of Gaussian blur. Blur and luminance had large effects at small base separations and relatively small effects at large separations. The data were also compared with the predictions of an ideal observer that was limited only by quantal fluctuations and the preneural factors up to the level of the photopigment in the photoreceptors.1 The predictions matched the data for base separations up to those yielding optimal sensitivity. However, at larger base separations, threshold increased and the effects of blur disappeared. Thus, at large separations relative efficiency is higher for blurred stimuli.
Vernier acuity and contrast sensitivity in monkeys and humans
Authors: Kiorpes Lynne , Movshon J. Anthony
Published: February 2023

In an effort to understand the neuronal basis of the abnormal visual processing that characterizes amblyopia, we have studied the development of visual performance in monkeys reared with either strabismus or unilateral image blur. We have measured vernier acuity, spatial resolution, and spatial contrast sensitivity in these animals. Compared to normal, the spatial contrast sensitivity function is displaced both downward in sensitivity and leftward in frequency in the treated eyes of these animals. They also have deficits in vernier acuity—often larger than the displacements of the contrast sensitivity functions—and we wished to know whether these were predictable from the contrast sensitivity changes. We have explored the relationship between the two measures using a contemporary spatial vision model (Watson, 1983), but this analysis requires more detailed knowledge of the empirical relation between contrast sensitivity and vernier acuity. To approach this we have measured the effect of reducing the level of illumination on human contrast sensitivity and vernier acuity. These measurements show that reducing luminance in human observers produces linked changes in both contrast sensitivity and vernier acuity resembling those seen in our abnormally reared monkeys. This suggests that the changes observed in multiple measures of visual performance may be straightforwardly related.
Some examples of practical design integrating geometrical and physical optics
Authors: Viswanathan V. K.
Published: February 2023

Helios was a typical Los Alamos National Laboratory CO2 laser fusion system. Each of its eight beams delivered 2 TW in a 120-µm spot with peak intensity exceeding 1016W/cm2. The optical system contained more than 100 elements in eight identical paths, each ~120 m long. The other example discussed is the resonator design for the RF linac-based free electron lasers which produce a thin, pencillike beam because of the nature of the gain volume. The uses and limitations of geometrical and physical optics techniques in the optical design and analysis of these systems is discussed.
Refractive analog for modeling electrostatic ion lenses
Authors: Sweatt William C. , Miller Paul A.
Published: February 2023

Cylindrically symmetric electrostatic lenses are used to focus ions to delineate integrated circuit features in microlithography. In the image projection configuration, ions from a submillimeter source are accelerated, transmitted through a stencil mask that contains the circuit pattern information, and focused onto a target wafer. Electrostatic lens design is computationally intensive. We have developed a refractive analog that enables use of faster optical design codes to treat the electrostatic problem. We employ a series of plano-convex lenses of vanishing thickness and high refractive index, with the convex surfaces described by eighth-order polynomials. The index varies between lenses with local voltage. In a test problem, a 12-cm diam mask was imaged by a single, 75-kV, 48-cm diam lens onto a target plane 200 cm away with nominal image magnification of — 1/6. The analog employed 400 refractive lenses. Meridional rays were traced through field points, and Coddington’s equations and a primary lateral color formalism were used to determine image quality. The analog calculation was performed rapidly on a PC; the trajectory code employed a supercomputer.