bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection and transmission properties of light incident on the human eye
Authors: Lemus T. , Lakshminarayanan V. , Zaleski E.
Published: February 2023

We have derived the reflection and transmission coefficients for two planes of light polarization incident on the human eye. The Fresnel equations for planar media have been modified into a form suitable for curved interfaces. This methodology is then utilized as a basis for the cornea and crystalline lens calculations. Light transmission and scattering properties along the visual axis are computed with it. By using this, a comparison with the Perkinje images is performed. From this we proceed to analyze the amount of transmitted light impinging on the retina. Finally, some comments concerning birefringence properties in the eye are included based on the coefficient derivations.
Color cross talk in photorefractive LiNbO3
Authors: Mayers A. W. , Rajan S. , Yu F. T. S.
Published: February 2023

Photorefractive LiNbO3 is an attractive material for the recording of real-time volume holograms for optical signal processing. Its ability to maintain holographic gratings for extended periods, coupled with the relative simplicity that it allows in system construction, have lead to its widespread use in electro-optic devices. Angular and wavelength multiplexing techniques have been developed to efficiently utilize the large storage capacity of the material. However, when transmission holograms are recorded, color cross talk can occur between gratings written by one wavelength and read out by a different wavelength. This effect degrades the efficiency of the wavelength multiplexing technique. In this paper, we explore the variation in the diffraction efficiency as a function of the input angle of the volume hologram gratings. In addition, when the grating writing process is performed in parallel, we observe cascading of the cross talk, leading to higher order diffractions. This effect severely limits the capabilities of performing color signal processing by using multiple wavelengths simultaneously.
Mode-locked Ti:sapphire: from 100 ps to 20 fs
Authors: Kafka J. D. , Pieterse J. W. , Watts M. L.
Published: February 2023

We have produced transform limited pulses ranging from 100 ps to 40 fs duration from a Ti:sapphire laser. Output powers in excess of 1 W and peak powers of 0.5 MW have been observed. We describe the technique of regenerative mode locking and present evidence that a transient with a peak power of more than 10 kW is required to initiate mode locking. The role of group velocity dispersion is highlighted, and a value of −750 fs2 is measured for the group delay dispersion in an operating laser. We describe the limits on both the power and pulse width obtainable from this laser and present pulse compression experiments that produce 17 fs pulses with 70 mW of average power. Recently, we have constructed a regenerative amplifier pumped by a cw argon ion laser and have generated 120 fs pulses with 1.2 μJ of energy. These pulses have been used to generate a continuum at a repetition rate of 200 kHz. Finally, we will report on the synchronization of two mode-locked Ti:sapphire lasers and demonstrate a technique for performing two color pump-probe experiments with better than 150 fs resolution.
Analysis of operation of an n2 effect mode-locked laser: reduction of self-mode-locking threshold
Authors: Pearson G. W. , Radzewicz C. , Krasinski J. S.
Published: February 2023

A numerical model was developed that propagates beams inside cavities containing gain, separate nonlinear media, and apertures. The model, using Hankel transforms, calculates radial field distributions in cavities and rigorously calculates losses for given intensities in ring or standing wave lasers. We investigated the influence of aperture position, aperture size, nonlinear crystal position, and nonlinearity of the crystal on laser losses versus intracavity power. The model was used to optimize the design of an n2 mode-locked laser. Although previous works show a linear relation between intracavity power and losses, we found large deviations even at low power when using high-n2 crystals. Increased power results initially in a decrease of the losses, but eventually the losses increase even above the initial level. The minimum loss level is critically dependent on crystal and aperture positions. For an 8 mm CdS crystal used as a nonlinear medium, the losses vs. power slope was increased by a factor of 400 with respect to a cavity utilizing a single Ti-sapphire crystal, which is crucial for low power self starting mode-locked lasers.
Theories of visual texture perception
Authors: Bergen James R.
Published: February 2023

The development of theories of visual texture perception is reviewed in the context of recent computational approaches. Visual texture is difficult to define precisely; one definition is that it is the visual phenomenon underlying the perception of the texture of surfaces of objects. There have been two major thrusts in thinking about texture segregation phenomena: one begins with the stimulus intensity distribution and the other with the perceptual entities that it contains. The history of the development of these two schools of thought can be described as a slow convergence toward an intermediate point. The former approach is characteristic of the work of L. A. Jones and other authors in the 1940s and early 1950s and of the early work of Bela Julesz and his various colleagues in the 1960s and early 1970s. The other approach is characteristic of the work of Jacob Beck and other perceptual psychological work on texture, which has its roots in the Gestalt theories of grouping and integration. The constructs used in recent computational work in texture modeling exist at a level somewhere between a simple description of image intensities and a true representation of meaningful perceptual objects.
Combining multiple cues to spatial location
Authors: Landy Michael S.
Published: February 2023

Previous work1 suggests that perceived depth from multiple cues is a weighted average of the depth estimated by using each cue. A cue's weight is decreased if the cue is less reliable or is strongly discrepant from other cues. These ideas were confirmed empirically by using perturbation analysis: perceived depth was measured in a multi-cue stimulus in which depth portrayed by one of the cues was varied. We suggest that this entire framework (the statistical model of cue combination measured by using perturbation analysis) may be applied to judgments of spatial location involving multiple location cues. Rivest and Cavanagh (ARVO, 1991) showed that additional edge cues can increase localization precision. Our statistical model predicts this. It also predicts perceived location when cues are inconsistent. In our experiments, stimuli consisted of multiple line segments. An edge was indicated by a gradient in line length, orientation, contrast, blur, and/or density. The edge location indicated by each cue was separately manipulated, as was the reliability of each cue (by noise manipulations). Preliminary results indicate that perceived spatial location is a weighted average of the locations indicated by individual cues and that the most reliable cues are given more weight. When one cue is strongly discrepant, it is no longer averaged with the other cues and two edges are perceived. Dependence between cues is also seen (e.g., lowering contrast or shortening length decreases orientation cue reliability).
(Pb,La)(Zr,Ti)O3, (Sr,Ba)TiO3, Ba2NaNb5O15, BaTiO3, LiNbO3, KNbO3, KTiOPO4, beta-BaB2O4, and LiB3O5 thin films for electrooptic applications
Authors: Wu Adam Y.
Published: February 2023

Thin films of (Pb,La)(Zr,Ti)O3, (Sr,Ba)TiO3, Ba2NaNb5O15, BaTiO3, LiNbO3, KNbO3, KTiOPO4, beta-BaB2O4, and LiB3O5, some of them highly oriented, have been deposited on various substrates by using rf magnetron sputtering and/or solution coating methods. All the films have the correct crystal structure and stoichiometry. Electro-optic effects and second harmonic generation in these films have been measured and will be presented. The potential applications of these films for integrated optics will be discussed.
Determination of complex nonlinear coefficients of absorbing media
Authors: Sanghadasa Mohan , Barr Thomas A. , Gregory Don A.
Published: February 2023

In determining the nonlinear coefficients of organic materials, it has become customary to ignore the phase shifts they generate. Many results reported so far are found to vary from one to another, for various reasons, including experimental errors. Many organic materials show absorption in the visible region, often near the second harmonic (SH) frequency. This damping often leads to broadening of the electronic transitions; hence nonlinear coefficients become complex in the vicinity of the reasonant frequency. Ignoring this factor may lead to erroneous results, especially in comparing nonlinear optical properties of various materials. Therefore, determination of both the magnitude and the phase of nonlinear coefficients is essential in order to understand the nonlinearity in most of the organic materials. A new method to determine complex microscopic nonlinear coefficients of absorbing organic materials is introduced. This method is based on a third-order nonlinear process known as the electric field induced second harmonic generation (EFISH). The design, construction, and operation of the experimental setup are presented, and experimental errors associated with the traditional EFISH experiment are also discussed.
Quantum nondemolition measurement of atomic momentum
Authors: Wilkens M. , Sleator T.
Published: February 2023

In two recent papers,1,2 it was shown how the interaction of a two-level atom with a standing laser field allows for a QND measurement of the atomic position using a quadrature component of the laser field as a meter. Here we demonstrate a complementary scheme in which a quadrature component of a propagating laser wave acts as the meter for a QND measurement of the atomic momentum. The measurement is based on a detectable phase shift of the cavity mode that results from the atom-field interaction. The principal characteristics of the measurement scheme are presented. We demonstrate how a selective version of the measurement scheme may be used to tailor an atomic wave function and to turn the measurement scheme into a "virtual beam handler."
Photoinduced second harmonic generation (SHG) in rare earth doped glass fibers
Authors: Krol D. M. , DiGiovanni D. J. , Bhandarkar K.
Published: February 2023

Photoinduced χ(2) gratings can be written in optical fibers by simultaneous irradiation with beams at co and 2ω. Although this phenomenon is not understood in detail, the experimental results show that the presence of optically active centers in the fiber is essential for the observation of this effect. We have studied photoinduced SHG in rare earth doped aluminosilicate fibers. In addition to measurements at 1064 /532 nm with a mode-locked Nd–YAG laser, we have investigated the dependence of the induced second harmonic intensity on the wavelengths of the writing beams by using a mode-locked Ti–sapphire laser. In a Tm-doped fiber we find a ≈103 increase in the induced SH intensity when the wavelength is tuned to the maximum of the 3H4 → 3F4 absorption of Tm3+ at 785 nm. These results show the importance of resonance enhancement of the nonlinear optical process that is responsible for χ(2) grating formation. We will also present results for other rare earth ions and their implications for understanding the origin of SHG in optical fibers.
Photoconductivity measurements in preforms and optical fibers
Authors: Lan Q. , Osterberg U.
Published: February 2023

Photoconductivity and photodielectric measurements of preforms and optical fibers have been performed. The measurements were done by using a noncontact microwave resonator technique. The photoinduced conductivity was measured to be 4 × 10–7 Ω–1 cm4 by using UV illumination at either 250 nm or 300 nm. In addition, a photodielectric shift of 500 kHz was measured. This shift amounts to an increase in the refractive index and indicates that there are shallow (~1–10 meV) polarizable traps just below the conduction band of the glass.
Prolonged temporal modulation and the interaction of color mechanisms
Authors: Shapiro Arthur G. , Zaidi Qasim
Published: February 2023

We present evidence that the visual system adapts to prolonged correlated stimulation of the chromatic cardinal mechanisms of Krauskopf et al. (1982) by changing the amount of interaction. Interaction between mechanisms was estimated from threshold differences parallel to one chromatic axis, measured at various levels of the orthogonal chromatic axis. Compared to the amount of interaction measured under neutral adaptation, there was no change following habituation along a cardinal axis, but there were changes following habituation along lines intermediate to the cardinal axes. This change in interaction is similar to Barlow's (1990) adaptive decorrelation processes and provides a more efficient representation of chromatic signals. We also present a model that uses this change in interaction to explain habituation results, including those of Krauskopf et al. (1986), without invoking higher-order color mechanisms.
Theory of photorefractive time-division demultiplexing
Authors: Khoury J. , Cronin-Golomb M. , Woods C.
Published: February 2023

Previous work has presented an optical approach to frequency- division multiplexing that allows entire images to be demultiplexed in a single operation. In this paper, we introduce the photorefractive theory for baseband transmission and demultiplexing of video images. In addition, we introduce the photorefractive linear theory for calculating the number of images that can be demultiplexed. Our calculation shows that given our assumptions, it is theoretically possible to demultiplex a large number of images for materials with small electro-optic coefficients. When a photorefractive medium that has a large electro-optic coefficient is used, then there is significant noise that arises because of non-linear interactions within the crystal. Increasing the number of stored images reduces the recall efficiency but does not change this noise.
Coherent imaging through turbulence and the double passage effect
Authors: Solomon C. J.
Published: February 2023

It is well known that the average image intensity of an incoherently illuminated object is severely degraded when viewed through atmospheric turbulence. To overcome this limitation, techniques such as speckle interferometry, bispectral analysis, and speckle holography have been developed. The problem of imaging a coherently illuminated object through turbulence is examined here. When a deterministic object is coherently illuminated and viewed through the same turbulence (double passage), the time-averaged image can be shown to contain diffraction-limited information on the object amplitude. Although the information is difficult to recover for a general aperture, the use of a suitable nonredundant aperture allows the information to be recovered quite simply. It is further shown that the use of a simple polarization discrimination scheme allows the information to be retrieved without time-averaging over the turbulence statistics. Experimental results that give qualitative confirmation of theoretical predictions are presented. Phase retrieval from the Fourier modulus has been successfully used on computer simulated data.
Birefringent light valve optimization for coherent processors
Authors: Lebreton Guy
Published: February 2023

Spectrum analysis and correlation are the basic tools for any coherent optical processor. In both cases, it is acceptable to lose some resolution in the image source plane, e.g., by a factor of 2, to improve the shape of the PSF or the SNR in the Fourier plane. This can be done with classical techniques of linear filtering. It is possible to restore the space invariance, destroyed by the flatness defects in the light valve, that is necessary for a correlator. In Fourier spectrum analysis, coding techniques for the windows where the signal is written on the light valve enables customizing of the resolution independently on both axes. In addition to correction capabilities, techniques developed for signal or array antenna processing are shown to give a quantitative evaluation of the performance comparisons of different light valves.
Rare-earth-doped silica waveguides fabricated by flame hydrolysis deposition and aerosol doping
Authors: Bebbington J. A. , Barbarossa G. , Bonar J. R. , Aitchison J. S.
Published: February 2023

We have fabricated rare-earth-doped SiO2-P2O5 planar films on silicon substrate by using flame hydrolysis deposition, incorporating the rare-earth ions by an aerosol doping technique, for the first time to our knowledge. Rare-earth-doping levels in the glass were dependant on the nebulized solution strength and the delivery rate of the aerosol to the torch. The aerosol doping technique has the advantage over solution doping of directly incorporating the rare-earth ions into the soot during the deposition and giving control of the doping profile through the film by contolling the transfer of the aerosol to the torch during the deposition. The aerosol doping technique is described, as well as the fabrication and optical assessment of channel waveguides with a view to realizing waveguide lasers. Moreover, the long term goal is to accomplish mono­lithic integration of active and passive optical components. This may be achieved by selective area doping of planar films. The method of selective area doping is discussed for aerosol doping.
Identifying the phase operator in quantum optics
Authors: Mertz Lawrence N.
Published: February 2023

The phase operator is deemed to be the same as the position operator. Statistical rather than Heisenberg uncertainty must then couple the quadrature field operators.
Quantum state resolved cis-trans-isomerization dynamics in S1 states of isolated linear polyenes
Authors: Petek H. , Bell A. J. , Christensen R. L. , Yoshihara K.
Published: February 2023

Fluorescence excitation and emission spectra of the symmetry for bidden and 21A
g
← 11A
g
(S1 ← S0) and strongly allowed 11B
u
← 11A
g
(S2 ← S0) transitions of several unsubstituted and methyl substituted linear polyenes are measured in free jet expansions. Activation barriers of <200 cm−1 and ~2000 cm−1 for nonradiative decay in S1 states of trienes and tetraenes are determined from measured fluorescence lifetimes. By analogy to previous condensed phase studies, the nonradiative channel is assigned to cis-trans isomerization. Octatetraene fluorescence lifetimes have a quantum-state dependence, which is ascribed to state specific tunneling rates through the isomerization barrier. Short lifetimes are observed mainly for a
u
and b
g
vibronic symmetry modes, which are more strongly coupled to the isomerization coordinate than are the a
g
and b
u
symmetry Franck-Condon and Herzberg-Teller active modes. In addition, S2 ← S0 spectra of tetraenes show Lorentzian line shapes with energy dependent widths of 10–60 cm−1 due to internal conversion to S1 states on a <500 fs time scale.
S-cone ERGs and S-cone acuity in patients with retinitis pigmentosa (RP)
Authors: Swanson William H. , Birch David G. , Anderson Jane L.
Published: February 2023

Increment thresh old studies have reported selective S-cone damage within the macula in RP. To evaluate widespread S-cone damage, we obtained S-cone ERGs with a 50° field from 11 patients with RP who had detectable full field 30-Hz flicker ERGs. To evaluate peak macular S-cone density, we also measured S-cone acuity. S-cone amplitudes ranged from 0.6 to 1.4 log units below normal, while amplitudes for L- and M-cones ranged from 0.0 to 0.9 log unit below nor mal. Full intensity-response functions could only be measured in five patients; four had normal semisaturation constants, and all five functions were consistent with the primary loss being decreased number of photoreceptors rather than decreased photoreceptor sensitivity. S-cone acuity was normal for eight patients, including four with extinguished S-cone ERGs. These data suggest that peak macular S-cone density may be normal despite widespread loss of S-cones across the posterior pole. In patients with RP, S-cone loss seems to follow the pattern previously seen for L- and M-cones, with foveal sparing despite widespread degeneration.
High fidelity phase conjugate mirror
Authors: Abdeldayem Hossin , Mago V. K. , Kapoor Rakesh , Venkateswarlu P. , Sekhar P. Chandra , George M. C.
Published: February 2023

A phase conjugate mirror with excellent fidelity and high reflectivity of >50% was obtained from disodium fluorescein doped in boric acid glass by degenerate four wave mixing, by using a cw Ar+ laser at 488 nm. The third order nonlinear susceptibility was estimated to be of the order of ~10 esu. The nonlinear mechanism accountable for the grating formation was found to be the resonant enhancement by the excited singlet and triplet states. Nine samples of different dye concentrations in the glass were pre pared. The grating decay times by degenerate four wave mixing and holographic process using a He-Ne laser as a reading beam were found to be concentration independent. The grating decay curves from the above mentioned techniques as well as the phosphorescence decays were found each to have two decay times of the order 0.1 and 0.03 s, 0.3 and 0.07 s, and 0.7 and 0.2 s, respectively. Spectroscopic studies of the sample at room and liquid nitrogen temperatures revealed the reasons for the presence of two decay times for each curve to be phosphorescence and delayed fluorescence. The discrepancies between the decay times for each process above will be discussed.
Nonlinear optics of anisotropic optomechanical media
Authors: Rogovin D. , Shen T. P. , Scholl J.
Published: February 2023

We examine microwave phase conjugation using three-dimensional arrays of electrically anisotropic particles that are mechanically supported but free to rotate and form orientation gratings.
Particulate sizing and the use of wavelength dependence to measure axial dispersion
Authors: George Nicholas , Wang Shen-Ge
Published: February 2023

Particle measurements are of importance in the study of aerosols, combustion processes, and pharmaceuticals. In this report, first we briefly review a simple derivation of an inversion formula from basic principles. We describe a modification to the usual form based upon intensity superposition so that one has a form that is accurate at tiny scattering angles. Then, we present the results of a new study of the wavelength dependence of the optical transform of a particulate distribution. Starting with the idealized amplitude transmittance, p(x−x
m
,y−y
m
)for a particle at spatial position (x
m
,y
m
) and taking the Fourier transform, one finds immediately the exponential term given by exp [−i2π(f
x
x
m
+ fY
m
)] in which the transform frequencies are f
x
= ξν/(Fc) and f
y
= ην/(Fc). We show how this exponent contains the essence of the temporal frequency dependence of the speckle pattern for the particulate cloud. We calculate the second moment of the intensity in the optical transform. We prove theoretically that it is possible to measure the axial distribution of a particulate sample simply by gathering optical transform data by using illumination by a tunable laser. This novel technique is then demonstrated with (1) computer simulations and (2) masks with various axial distributions. Some concluding remarks will also be made about the use of neural network software in re mote sensing of particulate sizing and spatial distributions.
Stability of error diffusion
Authors: Fan Zhigang
Published: February 2023

Error diffusion is an important technique for digital halftoning. The error diffusion system is required to be stable to guarantee its proper operation. It can be shown that an inappropriate choice of error diffusion coefficients can cause unlimited quantization error, which masks the input and generates unacceptable output images. There are many different definitions of stability. Here we are particularly interested in a bounded quantization error. A BIBO (bounded input, bounded output) type definition is adopted. The error diffusion is considered to be stable if and only if quantization error is bounded for any bounded input sequence. The stability is governed by the impulse response of the filter associated with the error diffusion process. The stability conditions are discussed in the presentation.
Speckle generation by phase-only spatial light modulators
Authors: Cohn Robert W. , Nonnenkamp Robert J.
Published: February 2023

Spatial light modulators with a range of 2π phase modulation, high diffraction efficiency, and video frame rate operation are now becoming available. Innaccurate set ting of the phase at each pixel can arise from several sources, e.g., thermal noise on SLM control signals, quantization of signal levels, and non-identical response of pixels to signals. Random phase errors reduce the intensity of desired diffraction patterns and increase the diffuse background of speckle, thus reducing contrast. We present analytic expressions for the average intensity and variance of the angular spectrum of phase-only transmittance. Errors in position and tilt of each pixel are treated as independent and identically distributed random variables. These assumptions are general enough to describe most deformable mirror modulators and other phase-only SLMs in conditions that can be achieved in the laboratory. We present a specific simulation showing the effects of phase errors on phase-only correlation. The number of operations used to calculate the expectations is on the same order of magnitude as that required for the deterministic calculation of diffraction patterns.
Relaxation oscillations in pulsed oxygen-iodine lasers
Authors: Shakir Sami A. , Erkkila John H.
Published: February 2023

High power pulses can be achieved in chemical oxygen-iodine lasers by rapid gain or loss modulation. This produces the ideal beam format for numerous laser applications. When these lasers are pulsed, relaxation oscillations are sometimes observed. We develop and analyze conditions for the existence of relaxation oscillations and derive expressions for the period and pulse decay rate. The temporal evolution of the photon density follows a damped harmonic oscillator equation. The derived expressions for the period are in good agreement with more detailed numerical simulations of the oxygen-iodine laser system. In particular, we identify conditions for the disappearance of the oscillations. The dependence of these oscillations on O2(1Δ) and iodine partial pressures is presented.
Optical generation of terahertz pulses from polarized excitons in quantum wells
Authors: Planken P. C. M. , Nuss M. C.
Published: February 2023

Until recently, it was believed that the generation of 1 terahertz pulses from the surface of a bulk semiconductor was caused by transient transport currents in the surface depletion layer of the material. We have generated terahertz pulses from an Al0.3Ga0.7As/ GaAs MQW sample after illumination with a 100 fs laser pulse, with an amplitude comparable to the one from a bulk GaAs sample. Since transport current in a quantum well is inhibited significantly, this proves that the radiation is generated by a recently proposed additional mechanism used to explain the creation of terahertz pulses from the surface of semiconductors. This explanation is based on the optical creation of electron-hole pairs in states in which they are already polarized. This leads to a time- dependent total polarization P that grows with the integrated pulse energy and hence radiates an electrical transient. In a wide MQW sample consisting of 15 periods of 175-Å GaAs wells separated by 150-Å Al0.3Ga0.7 As barriers, we observe an oscillatory terahertz signal lasting for several picoseconds when we coherently excite both the light hole and the heavy hole excitons. The oscillation frequency matches the light hole-heavy hole energy splitting, and we attribute the signal to a beating between the two.
Reactive-ion etching of rib waveguides in GaAs/AlGaAs using CCl2F2/O2
Authors: Cites J. S. , Bloemer M. J. , Ashley P. R. , Myneni K. , Mantovani J. G.
Published: February 2023

Reactive-ion etching to form rib waveguides in semiconductors is preferable to wet etching because of increased uniformity, better depth control, reduced mask under-cutting, and reduced side-wall slope. In this summary we report the fabrication of single mode rib waveguides in GaAs/AlGaAs quantum well systems by using CCl2F2/O2. The self-aligned oxidized Ti etch mask defines the electrodes and the ribs in a one step process. CCl2F2 was selected as the etchant because of its combination of high etch rate in GaAs and nontoxicity. The oxidized Ti mask used has provided the necessary etch resistance needed for deep etching, the result of the continuous oxidation of the Ti by the oxygen rich plasma. It is also easily removed for electrode contacts and adheres well to the gold electrode. The sample was an MBE grown waveguide on a Si doped {100} substrate. Ohmic contacts of gold/chromium/gold (10 nm/25 nm/200 nm) were e-beam deposited followed by 350 nm of Ti. Waveguides were patterned on the Ti by using photoresist and a chemical etch of 100:1 HF. Optical properties of the waveguide will be presented and compared with those of chemically etched waveguides.
High repetition rate AgGaSe2 optical parametric oscillator
Authors: Budni P. A. , Knights M. G. , Chicklis E. P. , Schepler K. L.
Published: February 2023

A AgGaSe2 OPO pumped at kilohertz repetition rates has been demonstrated. The pump laser consisted of a diode-pumped oscillator and a double-pass, tungsten-lamp-pumped amplifier. Both the Tm, Ho:YLF oscillator crystal and the Er, Tm, Ho:YLF amplifier crystal were cooled to 77 K with liquid nitrogen. An acousto-optic Q-switch allowed operation throughout the 1–50 kHz range with pulse widths of 15 ns at 2.5 kHz and 30 ns at 5.0 kHz. Average output powers up to 10 W were demonstrated with 1100 W of tungsten lamp power and 2 W of oscillator power. The OPO resonator used a 5 m radius of curvature input mirror coated to be highly transmissive at 2 μm and highly reflective in the 3–5 μm region. The output mirror was piano and 80% reflective in the 3–5 μm region. Physical resonator length was 4.5 cm. Two anti-reflection coated AgGaSe2 crystals were used: one, 34 mm long with 2.1 μm loss of α = 0.024 cm−1 and a standard coating; the other, 30 mm long with 2.1 μm loss of α = 0.013 cm−1 and an improved polish and coating. At 2.5 kHz, the low-loss, improved-coating crystal produced 740 mW of 4 μm output with 5.4 W of 2 μm input and a 1/e2 beam diameter of 2 mm. With a pump beam diameter of 1 mm, 2.3 W of pump power generated 550 mW of OPO output power, a conversion efficiency of 24%. The standard-coating crystal demonstrated only 100 mW of 4 μm output because of damage limitations. In all cases, maximum OPO input power was limited by damage to the AgGaSe2 crystal surface. However, conversion efficiency was found to peak at pump powers below the damage threshold. This saturation of conversion efficiency was most likely a thermal effect. The improved-coating crystal consistently demonstrated damage levels a factor of two better than those of the standard-coating crystal.
Thermal lensing and power scaling of a AgGaSe2 OPO
Authors: Marquardt C. L. , Cooper D. G. , Budni P. A. , Knights M. G. , Schepler K. L. , DeDomenico R. , Catella G. C.
Published: February 2023

The 2-μm pumped AgGaSe2 OPO is currently limited to outputs below 1 W and pulse recognition frequencies of a few kilohertz, apparently because of thermal lensing. Conflicting values for K and dn/dT and the lack of accurate 2-μm absorption data have severely hampered predictions of thermal focusing from material properties. We present results of polarized 2-μm laser calorimetry and extracavity thermal lens measurements on AgGaSe2 samples grown at two laboratories over the past 5 years. We show that the 2-μm absorption is due primarily to an e-polarized extrinsic band. Even for our best material, the thermal focal length can be comparable to the crystal length (in a typical OPO configuration) at pump powers of only a few watts. We find no astigmatism due to crystalline anisotropy, and we demonstrate the possibility of intracavity optical compensation. We have also achieved an order of magnitude reduction in thermal focusing by cooling the crystal to 77 K.
Origin and shape of the Ar2 excimer band at 128 nm excited in a supersonic jet
Authors: Kiik M. J. , Dube P. , Stoicheff B. P.
Published: February 2023

The Ar2 excimer band at 128 nm has generally been thought to arise from excimers in the closely spaced

A

 
3

Σ
u
+

(

1
u

)

and

B

 
1

Σ
u
+

(

0
u
+

)

states. We have investigated this designation spectroscopically by irradiating the dc discharge plasma of Ar2 after supersonic expansion with the beam of a tunable titanium–sapphire laser to probe the 3p54s manifold of atomic Ar and simultaneously monitoring the effects on atomic transitions as well as on the 128 nm band of Ar2. Intensity increases and decreases of up to 5% were measured in the 128 nm band, depending on the wavelength of the incident radiation. The analysis of these results indicates that under the present discharge conditions, the 128 nm band is primarily due to excimers in the

A

 
3

Σ
u
+

(

1
u

)

state, formed from atoms in the 4s[3/2]2 level. It is also shown that the observed FWHM bandwidth of 8.7 nm can be explained by significant vibrational cooling of the excimer after expansion, with ≈80% population in the v = 0 level. Thus, when the laser was tuned to probe an absorption band of Ar2 at 985 nm, and a decrease in intensity of the 128 nm band was recorded having the shape and bandwidth of the 128 nm band, this was proof that the 985 nm band originates from the

A

 
3

Σ
u
+

(

1
u

)

(

v
=
0

)

state.
Virtual reality as a museum exhibit
Authors: Coombs Ted , Coombs Jason
Published: February 2023

Virtual reality is a field of three dimensional computer modeling that allows the viewer to be immersed in the model. Use of goggles, earphones, and a sensory glove brings the viewer into an interactive computer generated world. The goggles create the appearance of three dimensions. The glove serves two purposes. First, it provides feedback to the computer to move a computer glove. Second, it will provide physical force when the computer modelled hand touches a computer generated physical object. Therefore, viewers believe they have touched something. In complex models, texture can be felt. Museums will be able to use virtual reality as a demonstration tool to allow the museum attendees to view everything from the creation of the universe to the principles of optics. Not only will they be able to be active participants, but the use of a glove or other interactive device will allow the participants to touch and affect the images they are viewing. Audio can accompany the 3D images to enhance the effect of being a part of what you are viewing.
Motion detection in nonlinear lateral inhibitory neural networks
Authors: Bouzerdoum A. , Pinter R. B.
Published: February 2023

Motion is an important component of vision for flying insects. Optomotor reactions serve to minimize involuntary deviations of trajectories and stabilize the flight course. Insect optomotor responses are based on directional movement detection. The Reichardt correlation detector, essentially based on linear time-invariant filtering, cannot account for the saturation and adaptation properties exhibited by insect responses to motion. In this paper a directionally selective movement detecting (DSMD) neural network architecture, inspired by invertebrate vision, is presented. It is structurally and, to second order, functionally equivalent to a Reichardt detector, but it operates on the nonlinear mechanism of shunting lateral inhibition. Responses, under various constraints, of this DSMD neural network to moving patterns such as edges, bars, and sinusoidal gratings are investigated and compared to those of insect DSMD interneurons.
The role of early visual mechanisms in visual search
Authors: Chou K. L. , Geisler W. S.
Published: February 2023

We attempted to determine the extent to which visual search time is governed by the parallel and automatic front end of the visual system. The target patches and background fields were narrow-band-noise textures that differed in spatial frequency and/or orientation. In the first part of the experiment, accuracy for detecting the target in the background was measured as a function of eccentricity for many target-background pairs. In measuring these accuracy windows, the observer always knew the exact positions of the target. Because this 2AFC procedure minimizes the demand for high-level processing, the accuracy window should represent (approximately) the relative loss of information in the parallel front end. In the second part of the experiment, average search time was measured for the same targets and backgrounds that were used in the first part, except the targets were randomly located within the background region. We found that search time decreased monotonically as a function of the area under the accuracy window. These results support the hypothesis that the early visual mechanisms determine (for fixed sizes of the target and background regions) the rank-order search time across different combinations of target and background texture.
Discharge stability limits for pulsed CO2 and N2O lasers and their edge characteristics
Authors: Apollonov V. V. , Semenov S. K. , Firsov K. N.
Published: February 2023

The subject of the present investigation is the influence of the special additives to the mixture of CO2 and N2O lasers as well as the influence of electrode roughness on the fall of the volume self-sustained discharge (VSD) stability. The maximum time of the VSD stability was 12 µs for CO2lasers and 3.5 µs for N2O lasers. That is sufficient to pump discharge a unit with a 1 m3 volume. The kinetics of the low temperature plasma process and dynamics of spark channel growing have been investigated by intracavity laser spectroscopy and high speed photography.
Stability criteria for homogeneously broadened standing-wave lasers
Authors: Chenkosol Pitak , Casperson Lee W.
Published: February 2023

An important aspect of any study of laser instabilities is the question of the conditions under which spontaneous pulsations will or will not occur. Stability criteria for ring-laser oscillators have been given previously, and we have now obtained the stability criteria for the more complex but also more important standing-wave lasers. We have completed a study of the stability criteria for homogeneously broadened standing-wave lasers, and extensions of this work to the general mixed-broadened laser configurations are in progress. A specific new result is that the lowest possible value of the threshold parameter of a standing-wave homogeneously broadened laser for which perturbation instability can occur is about r = 34 when the laser is tuned to line center. This is to be contrasted with the much lower value r = 9 for ring lasers. The high value for standing-wave lasers means that this type of instability would be extremely difficult to observe. As the relative amount of inhomogeneous broadening is increased, the instability threshold parameter for standing-wave lasers drops toward r = 1. The effect of detuning on the stability criteria has also been investigated.
Generation of broadly wavelength tunable ultrashort pulses from cw mode-locked diode lasers
Authors: Yan Chi , Li Yuan , McInerney John G. , Jain R. K.
Published: February 2023

We will describe the use of a variety of mode-locking techniques, including the use of active mode locking and passive mode locking with Fabry-Perot saturable absorbers, to generate ultrashort pulses from broadly tunable external cavity single lateral mode cw diode lasers. We have tuned such lasers either directly with intracavity tuning elements (primarily gratings and birefringent filters) or by injection locking with external broadly tunable cw diode lasers, to obtain short pulse generation over relatively large tuning ranges (typically 350 Å). A comparison of the results obtained with the different mode-locking techniques and the advantages and disadvantages of each of these techniques will be described. Scaling of the results for obtaining broad tuning ranges with high output powers (>1 W average and >1 kW pulsed) and applications thereof (including high efficiency nonlinear frequency conversion) will be discussed.
An integrated optical phase modulator using a PbSe-clad BaF2 waveguide
Authors: Khodr M. F. , Sluss J. J. , Batchman T. E.
Published: February 2023

We present the design of an optical phase modulator using a PbSe-clad BaF2 waveguide on a CaF2 substrate. This materials combination is useful for integrated optical devices operating in the 3-5 µm wavelength range. The key property that controls the modulator is an induced change in the imaginary part of the PbSe permittivity ε
i
. We have investigated the behavior of the TE modes over a wide range of ε
i
for a free space wavelength of 3.4 µm. Our analysis shows that the TE0 mode propagates discretely in the PbSe if ε
i
<6.501. The discrete TE0 mode converts continuously to a TE1 mode propagating in the BaF2 for an incremental change Δε
i
. as small as 0.001. A phase modulator was designed for a PbSe cladding thickness of 0.026 µm, which coincides with the critical point where the discrete TE0 mode converts to a continuous TE1 mode for Δε = 0.001. Phase modulation is indicated by a large change in mode index value for a small induced change in the ε
i
of the PbSe. The attenuation at this critical point remains relatively constant, even though a large phase change is produced.
Theory of optical pulse propagation in the region between superfluorescence and amplified spontaneous emission
Authors: Ritchie Burke
Published: February 2023

The coupling of forward and backward propagating waves is studied theoretically in the transition region between superfluorescence (SF) and amplified spontaneous emission (ASE). To accomplish this a computer code has been written that solves Maxwell's equations in time and two spatial dimensions and accounts for counter-propagation, diffraction, and temporal coherence in the Bloch equations. Diffraction is ignored in the present calculations. In the SF regime the coupling is generally weak, as found by others; however, I have found a randomly occurring shot-to-shot coupling that is quite significant in cases where one wave, forward or backward, becomes established from quantum noise first in the amplified rod. In this case the wave that arises second is strongly coupled to the first. In the ASE regime the propagation shows strong forward-backward coupling and the characteristic spatial profile of the inversion that tends to zero at either end and to the small signal value of one in the middle of the amplifier. In the transion region the propagation shows mixed SF and ASE behavior.
Optical system design for measuring the level of melted glass
Authors: Zangaro R. A. , Pacheco M. T. T. , Spina F. D. , Lima C. J. , Melo A. B.
Published: February 2023

In this work we describe a system based on the reflection of a He-Ne laser beam on the glass surface. This glass level measuring laser system (GLEMLAS) can measure level variations as large as 10 mm with high accuracy. The GLEMLAS uses a 1 mW nonpolarized laser beam and a telescope to obtain the correct beam diameter. The beam is focused down on the CCD array by a 150 mm focal length cylindrical lens. A filter is positioned in front of the CCD array to avoid the blackbody radiation. The gas flow inside the oven produces strong turbulence in the medium density, producing fast variations in the refractive index along the laser beam path. Under these conditions the laser beam moves randomly. The GLEMLAS was tested, and it showed a range of ~10 mm, limited basically by the CCD size, the optical system, and the measuring accuracy. However, even when the glass level reaches the limit of the measuring range, it does not damage the system. Instead, it stops reading and it returns automatically to normal operation after the disturbance. The positioning of the GLEMLAS outside the oven makes the cooling requirement less critical and reduces maintenance costs.
Observation of the nonlinear magneto-optical Kerr effect in PtMnSb by second harmonic generation
Authors: Zink J. C. , Rau C. , Reif J. , Matthias E.
Published: February 2023

Using p-polarized fundamental light and near grazing incidence, we studied second harmonic generation (SHG) in reflection from a single-crystalline, ferromagnetic Heusler alloy. By varying the second harmonic polarization angle, we found a rotation of the polarization plane of the frequency-doubled light by about 14°. This is an extraordinarily high value and an order of magnitude larger than the linear Kerr angle of about 1 °. Thus, we propose the use of SHG as a sensitive detection technique for magnetization. Further, we tested the dependence of the SHG yield on the magnetization direction with circularly polarized light. We found a stronger yield when the circular polarization is parallel to the handedness defined by the magnetization and a reduced yield for the opposite case.
Maxwell-Gaussian optical beams
Authors: Erikson W.L. , Singh Surendra
Published: February 2023

Paraxial Gaussian-beam-like solutions of the scalar wave equation, often used to model laser beams, do not satisfy Maxwell's equations. Paraxial-beam-like solutions that satisfy Maxwell's equations are constructed from the solutions of the scalar wave equation. Polarization properties of these Maxwell-Gaussian beams in free space are discussed. It is found that a Maxwell-Gaussian beam linearly polarized in the x direction and propagating in the z direction has a weak cross polarization component in the y direction in addition to a longitudinal component in the direction of propagation. These properties are demonstrated by using light beams from an Ar-ion laser.
Fast evaluation of the effect of focal shift in focused, apertured Gaussian beams
Authors: Li Yajun
Published: February 2023

It was found both analytically and experimentally that when a Gaussian laser beam is focused by a thin lens and the waist of the beam is in the plane of the lens and is much smaller than the linear size of the lens, the point of absolute maximum irradiance is located on the axis but somewhere closer to the lens. This effect is referred to as focal shift. In this study, a formula is developed for fast computation of focal shift in focused, apertured Gaussian beams. This formula is a generalization of two previously known focal shift formulas, one for an unapertured Gaussian beam and the other for a plane-wave beam. The proposed formula brings no limitation to the level of beam truncation and gives the focal shift with an accuracy of about 90% or better. Since the point of absolute maximum irradiance in a focused field is near the plane where the field has a minimum spread, the proposed formula provides a convenient means to specify or to create the location of beam waist in a laser focusing system in which the fundamental circular mode of a laser beam is used.