bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal factors affecting the square-wave illusion
Authors: May James G.
Published: February 2023

Viewing a vertical triangle-wave grating often gives rise to the perception of a corrugated surface with alternating bars that approximate a square-wave luminance profile. This square-wave illusion contains other bistable aspects. Adjacent bars appear to be offset in depth, and the corrugated surface appears to be illuminated from one side or the other. Drifting the grating to the right or left biases the direction of apparent illumination. In the present investigation, a triangle-wave with a spatial frequency of 0.25 c/d was phase-alternated (180) at various rates. The first finding was that the square-wave illusion was totally suppressed at alternation rates greater than 3 Hz. At slower rates, observers reported that all aspects of the illusion could be perceived, but a bias in the direction of apparent illumination did not appear to be linked to the occurrence of a phase shift. At very slow rates of alternation (Hz), observers reported two possible perceptual experiences: (1) alternate bars appeared to move back and forth in counter-phase; or 2) bars appeared stationary and the direction of illumination appeared to change with each phase shift.
Stimulated photon echo modulation in praseodymium-doped crystals
Authors: Talagala P. , Kim M. K. , Kachru R.
Published: February 2023

When the intensity of photon echo in a two-level system is measured as a function of delay time of the two input pulses, one obtains a simple exponential decay with the characteristic phase relaxation time. When the two levels contain hyperfine structures, the interference among the hyperfine levels gives rise to modulation of the decay envelope. The Fourier transform of the modulation pattern reveals the hyperfine structure of the rare-earth ions. The hyperfine structure, and therefore the modulation pattern, are both sensitively affected by the crystal environment of the ionic site. We extend photon-echo modulation spectroscopy to three-pulse, stimulated photon-echo modulation, and we find that the stimulated echo modulation patterns are quite distinct from the two-pulse, photon-echo case and are affected by a different set of atomic and crystal interaction parameters. The modulation is measured, in several photon-echo transitions of praseodymium ions in lanthanum trifluoride and yttrium aluminum garnet crystals, as functions of delay times between first and second pulses and between first and third pulses. Comparison of the experimental results with density-matrix calculations allows us to determine hyperfine parameters that are not easily observed with two-pulse echo modulation.
Ring-mediated coupling of NH2 and CH3 modes in para-methylaniline
Authors: Yan Shuxin , Moore Teresa , Spangler Lee H.
Published: February 2023

Jet-cooled fluorescence-excitation spectra of aniline, aniline-ND2, p-methylaniline and p-methylaniline-ND2 will be presented. Two moderately intense peaks in the p-methylaniline spectrum show an unusual multiplet splitting that is not observed in the ring modes. These two transitions also show a large (100 cm−1) deuterium shift in the ND2 molecule and are thus assigned as evenquanta transitions involving the amine inversion and torsion. The corresponding peaks in aniline are not split, indicating that the splitting is due to the interaction of the CH3 torsion with large-amplitude amine motions. Given the large separation between the two groups and the evidence that the amine must be in motion (i.e., have a quantum or more in one of its large-amplitude normal modes), an unusual and dynamic coupling mechanism is suggested. We speculate that the amine motion causes an oscillation in the cloud of the ring that the methyl group responds to by means of the hyperconjugation interaction.
Single-atom cavity-enhanced absorption with injected squeezed vacuum: photon statistics
Authors: Rice P. R. , Pedrotti L. M. , Walden J.
Published: February 2023

We consider a single two-level atom in an optical cavity, in which the system is driven by a coherent driving field. In the bad-cavity limit, when the cavity loss rate is taken to be large compared to the atomic decay rate and atom-field coupling, the cavity field can be adiabatically eliminated from the equations of motion for the atomic operators. The main effect of the cavity in this limit is the enhancement of spontaneous emission into the cavity mode. For this model, the second-order intensity correlation function g(2)() has been shown to exhibit photon antibunching, sub-Poissonian photon number distributions, and other nonclassical effects.1 In this paper, analytic results are presented for g(2)() for both the transmitted and fluorescent light fields when broadband squeezed light is injected into the cavity. Effects of the squeezing on nonclassical behavior is examined.
Increased depth-of-field and stereo pairs of fluorescent and bright-field micrographs by means of inverse filtering
Authors: Khosla Deepak , Holmes Timothy J.
Published: February 2023

When the thickness of a specimen is greater than the depth of field (DOF) of a microscope, the observed image is obscured because parts of the specimen are in focus while other parts are out of focus. These out-of-focus obscurities can be partially removed by iterative algorithms involving three dimensional data sets. However, there are practical limitations in doing so; a full three-dimensional image restoration will require both large memory storage and a long processing time.
A cyclic shearing interferometer for collimating beams with short coherence times
Authors: Henning T. D. , Carlsten J. L.
Published: February 2023

Until now there has not been an accurate method for measuring the radius of curvature of a short-pulse or broad-band laser. This is because the standard shearing plate interferometer1 used to measure the radius of curvature of a beam cannot be used for beams with coherence times shorter than 70 ps. The adjustable, lateral shearing, cyclic shearing interferometer (CSI) solves this problem. The CSI produces a fringe pattern as does a standard shearing plate collimation tester, except that the CSI can be used on beams with coherence times Δtc as short as one picosecond, since the two beams in the interferometer follow nearly the same path. The CSI is easy to align, and the radius of curvature of the incident light beam can easily be computed once the distance between the fringes and the fringe's angle with respect to the horizontal is known. Comparison with data from a broad-band, XeCl laser (Δtc ~ 30 ps) confirms that the CSI performs as theory predicts.
The antiresonant ring in ultrafast excite-probe spectroscopy
Authors: Trebino Rick , Hayden Carl C.
Published: February 2023

The antiresonant ring (ARR), first introduced by Siegman, has found many applications, most recently in colliding-pulse mode-locked lasers.1 Here we introduce the use of the ARR as a detection arrangement for performing ultrafast excite-probe induced-absorption experiments, where it offers many advantages over current techniques. Specifically, the sample cell is placed off-center in the ARR, where an excitation beam interacts with only one of the two (probe) beams counterpropagating in the ring. On return to the beam splitter, the full probe intensity and any dc effects cancel out, and only the signal light due to transient effects leaks out of the ring as signal. This optical subtraction is more accurate than electronic subtraction. Also, by deliberately allowing some leakage from the ring, optical heterodyne detection (OHD) is possible, yielding both the absorption and refractive-index transients independently without constraining the beam polarizations (as in OHD polarization spectroscopy). By choosing the best leakage value, maximum signal-to-noise ratios are achieved in the presence of laser shot-to-shot jitter.2 In preliminary experiments using 1% leakage, we have improved the signal-to-noise ratio by a factor of five. This results agree with theory, which predicts even better values if less leakage is used.
Photonic switching using four-wave mixing with two pumps
Authors: Zhao Yang , Li Zhaolin
Published: February 2023

The switching scheme using four-wave mixing with two independent pumps has three inputs and four outputs. One of the inputs is chosen as the control beam. The intensity relationships among these inputs and outputs are studied by using the coupled-mode theory and boundary conditions. It is found that the output signal level is zero when the switch is off and is equal to the exact input signal level when the switch is on. The result indicates that these switching devices are ideal for cascaded use, which requires equal input and output level of the switch because the outputs of one stage will be the inputs of next stage. This property is different from those schemes using four-wave mixing with one independent pump,1 which has the output signal level different from the input signal level when the switch is on. The performance of the switching device is strongly dependent on the nonlinear factor of the interactions. The required control signal level for switching operation is lower when the nonlinear factor is large.
Space marching algorithm for calculating strong acousto-optic interaction of arbitrary fields
Authors: Korpel Adrian , Venzke Clark , Mehrl David
Published: February 2023

Our space marching algorithm is of the split-step Fourier transform type. In this method, space is divided in thin slices Δz. The first step involves the propagation of the angular plane wave spectrum of the incident light field through a slice as if the latter were homogeneous. At the exit of the slice the propagated plane waves are reassembled into an intermediate field. In the second step the intermediate field is multiplied by the x,y dependent transmission function of the slice as if the latter were a thin phase filter, induced by the sound. A similar technique (that does not necessarily involve the plane wave spectrum) is often called the beam propagation method, and has been used for the analysis of gratings before. In our case, however, we are interested in soundfields of arbitrary shape and–this feature ultimately constitutes the novelty of our method–in avoiding the processing of the sound carrier. The latter is not of intrinsic interest to us and merely uses up computer time in dealing with the fine inhomogeneous detail it induces. What the sound carrier does we know already: It splits each incident order of light up into three other ones when traversing a small distance Δz. In our algorithm we make use of this a priori knowledge to involve only the envelope or profile of the sound field in the simulation.
Trapped-ion frequency standards
Authors: Bergquist J. C.
Published: February 2023

Experimental research at NIST toward the realization of frequency standards of high accuracy is briefly reviewed. Our studies have concentrated on laser-cooled, stored ions since they offer several attractive features toward the achievement of high accuracy (better than one part in 1015). These features include long storage times which eliminate transit-time broadening, gentle confinement which is nearly nonperturbative to the internal level structure of the ion, and laser-cooling which can reduce motional shifts to small values. We have spectroscopically studied ions confined in Penning traps at low density and single ions in rf traps. An rf oscillator at a frequency near 303 MHz has been locked to a hyperfine transition in 9Be+ ions that are stored in a Penning trap and sympathetically laser-cooled. Stability was better than 3 × 10–12 is τ–½ and accuracy was better than one part in 1014. We have also probed an electric-quadrupole allowed transition (frequency ~1 × 1015 Hz) in a single, laser-cooled 199Hg+ ion stored in an rf Paul trap with extremely high resolution. The measured linewidth of this metastable transition is limited presently by the spectral purity of the laser to about 75 Hz. Finally, improvement of signal-to-noise ration by linear trap geometries will also be discussed.
Optical pumping of an atomic vapor with a frequency-modulated laser
Authors: Tremblay F. , Michaud A. , Beaubien J. , Cauchon É.
Published: February 2023

Rubidium maser and passive frequency standards performances rely on the efficiency of the optical pumping scheme. When using a semiconductor laser as the pumping source in such experiments, one found that the sharpness of the laser spectrum allows only the excitation of a small class of atomic velocities. The use of a frequency-modulated laser has shown great promise by largely increasing the overall pumping efficiency.1 Broadening of the narrow laser spectrum ensures the contribution of all classes of atomic velocities present in the vapor.2 Different modulation waveforms, amplitudes and frequencies have very important effects in overall optical pumping efficiency. We theoretically evaluate the efficiency of a frequency-modulated laser pumping source by studying deterministic as well as random modulation. Important considerations are obtained regarding the optimal conditions concerning the magnitude and the bandwidth of the modulation signal. Moreover a deterministic modulation must be used to lock the laser frequency by interrogating an atomic cell and synchronously detecting the transmitted intensity. Experiments conducted on a rubidium 87 maser optically pumped with a semiconductor laser confirm the predictions. In fact the oscillation of the maser was only possible with the help of the laser frequency modulation.
Measuring optical quality with a fiber optic double pass pointspread focal scanner
Authors: Howland B. , Denton D. D. , Howland N. C.
Published: February 2023

We describe a device for measuring the optical quality of a lens. It employs two fiber optic bundles which are randomly intermixed and combined at one end. Narrow band, spectrally filtered light is supplied to the mixed end through the "driving" bundle. This is collimated by a long focal length achromatic doublet. Behind the lens to be tested, near its focus, is placed a reflecting surface mounted on the tip of a micrometer. The fiber optic mixed end is imaged by the collimator and test lens on the reflecting surface of the micrometer, and re-imaged at the source. Aberrations of the test lens cause light from the driving bundle to spill over into the second bundle which is attached to a radiometer. By scanning the focus of the test lens with the micrometer a graph of measured light vs. focal position for different apertures is obtained. The method is extremely sensitive to spherical and longitudinal chromatic aberration and allows modern camera lenses to be sorted easily with respect to optical quality. A raytracing model is used to relate the shape of the focal plots to the wave aberrations of the lenses studied.
Piezoelectric fields and nonlinear optical susceptibilities [χ(2) and χ(3)] in certain II–VI strained layer superlattices
Authors: Jackson S. A.
Published: February 2023

Lattice-mismatch in (111) grown strained layer superlattices (SLS) can give rise to piezoelectric fields on the order of 104-105 V/cm.1,2 These fields lead to interesting nonlinear optical effects, which can depend on the density of free carriers. At low carrier density, there is an effect of the piezoelectric fields on the nonlinear susceptibilities due to parity mixing of the levels: [χ(2)], and due to piezoelectric field-driven changes in the carrier dispersion relations: [χ(3)]. In an SLS, grown on a buffer layer intermediate in concentration between the two active epilayers, we use a transfer matrix technique3 to obtain dispersion relations for the superlattice and an exact superlattice wavefunction. This is done within a single band model with momentum mixing of the bands due to zonefolding considered. Using these results we calculate χ(2) and χ(3) for a CdTe/ZnTe SLS. We find χ(2) ~ 10 × bulk GaAs. A large χ(3) results because of electric field modulated band nonparaboliticity in the SLS. We find χ(3) ~ 60 × bulk GaAs. The level broadening in the minibands demonstrates a strain-induced Franz-Keldysh effect in this system, whose explicit form varies with electric field. Finally, we consider the effect of screening on χ(3) as a function of carrier density.
Ultrafast dynamics of photorefractive gratings in undoped CdTe
Authors: Schroeder W. A. , Stark T. S. , Dawson M. D. , Boggess T. F. , Smirl A. L. , Valley G. C.
Published: February 2023

We recently developed a novel nondegenerate, polarization-rotation, transient-grating technique, which can be used to isolate and time resolve (with picosecond resolution) the dynamics of nonphotorefractive and photorefractive gratings in zincblende semiconductors. Here we use this technique to investigate the photorefractive grating in undoped CdTe. The grating was written by two 1 ps pulses at 960 nm generated by an amplified Styryl 13 dye laser system. At this wavelength, the space-charged field required for the photorefractive nonlinearity can only be formed between electronhole pairs, since free-carriers can only be generated by two-photon absorption in this material. A <5-ps pulse at 1.06 µm (generated by Raman-shifting a fraction of the 960-nm radiation in benzene) was used to read the photorefractive grating as a function of time delay. The measurements identified two contributions to the photorefractive effect: an initial transient response followed by a longer lived component that decays predominantly by ambipolar diffusion. The latter signal is therefore consistent with a photorefractive grating associated with the space-charged field between electron-hole pairs (i.e., the Dember field). Some possible origins of the initial transient signal, which indicates an enhanced photorefractive response on picosecond timescales, will be discussed.
Objective comparisons of statistical methods of image reconstruction
Authors: Gooley T. A. , Barrett H. H. , Denny J. L. , Seeley G. W.
Published: February 2023

In medical image reconstruction, one always has in mind the ultimate goal of obtaining the reconstruction that will yield the most accurate diagnosis given a specified task. The visual appearance of any reconstruction will depend on several factors including the method used to obtain the reconstruction. Statistical methods have been the topic of much recent interest in emission tomography. virtually all statistical methods attempt to find the reconstruction that agrees with the collected data to a degree that does not contradict any prior information assumed about the object. The prior information, and the way that one incorporates this information, is what typically distinguishes one statistical method of reconstruction from another. A plethora of methods exists and because of this, a natural question arises: which method should be used? While many methods have been investigated independent of others, an objective comparison of any of these methods is something that has not yet been sufficiently explored. In this presentation, we make objective comparisons of several statistical methods of image reconstruction. To do this, we define a specific task and use different reconstruction methods on a given class of objects. Based on the specified task, we make objective comparisons of the different methods of reconstruction through psychophysical studies and receiver operating characteristic analysis.
Shift-invariant imaging using the bispectrum
Authors: Newman J. Daniel , VanVranken R. C.
Published: February 2023

We describe the results of a new algorithm for processing a series of noise degraded and randomly shifting digital images using the bispectrum. The algorithm is shown to yield a reconstructed signal-to-noise ratio (SNR) improvement which is nearly equal to perfect frame stacking using no prior knowledge whatsoever. The technique is quite robust and has wide ranging applications for situations in which imaging platform stabilization and noise are problematic The algorithm is very efficient and can completely process 128 250 × 128 format image frames in less than ten minutes on a VAX workstation. This is significantly faster than other algorithms we are currently aware of. Comparisons of the bispectrum algorithm with perfect frame registration and an adaptive matched filter algorithm are given for a wide range of simulated data sets. The data sets include both shot noise limited simulations and background noise limited simulations. The results indicate that the technique is more robust than second order matched filter methods due to the inherent shift invariance of the bispectrum. A description of the algorithm is given. It is quite different from other image reconstruction algorithms we are aware of and holds out the possibility of real time digital image processing using only two or three transputer array boards.
n2 measurements through the inverse transmittance in a bistable laser diode
Authors: Calvani R. , Caponi R.
Published: February 2023

The optical parameters (in particular the nonlinear refractive index n2) of a bistable Fabry–Perot (FP) amplifier pumped by a similar GaAlAs laser have been evaluated from the optical bistability (OB) cycle of the operating device.1 This paper presents a new n2 measurement method, utilizing the same OB data through a linear fit of the single pass FP phase Φ.
Application of a sideband oodr Zeeman spectroscopy to diatomic molecules
Authors: McCarthy Michael C. , Field R. W.
Published: February 2023

In order to test simple atom-in-molecule concepts in the theory of the electronic structure of transition metal monohydrides and monohalides it is necessary to extract key electronic properties from the spectra of these molecules. Unfortunately, the spectra of diatomic molecules containing an atom with a partially filled d-shell are complex. Consequently, it is desirable to develop spectroscopic techniques and strategies whereby spectra can be simplified and rapid generation of diagnostically important spectral information is possible. Sideband optical-optical double resonance-Zeeman spectroscopy (SOODRZ) is one such technique. SOODRZ is one-laser, two-color, absorption-based technique which presents sub-Doppler Zeeman splittings in a simple, diagnostically useful format. Unlike other sub-Doppler techniques where complex Zeeman splitting patterns obscure the tuning coefficients of either the upper state or lower state, in SOODRZ, only two Zeeman resonance features (single upper and single lower state resonance) are observed. The Zeeman information (J, Q-dependent Zeeman tuning coefficients) can then be used for rotational and electronic assignment, we will illustrate the usefulness of SOODRZ by showing examples from the electronic spectrum of NiH. We will also discuss the lineshape and sensitivity of SOODRZ for a variety of detection schemes using both electro-optic and acousto-optic modulators.
Resonant Raman scattering and photoluminescence studies in CdS microcrystal systems
Authors: Zhao Xue-Shu , Schroeder John , Persans Peter D. , Tolmie Richard
Published: February 2023

Pressure-tuned resonant Raman scattering was used to determine the bandgap shift due to quantum size effects of microcrystallite CdS in glass composites and colloids. The phase transition behavior in microcrystallite CdS systems is quite different from that in bulk CdS. We attribute the different behavior to the large number of defects (vacancies) in microcrystallite CdS systems. Then we systematically investigated these defect properties in terms of their pressure coefficients by means of the photoluminescence peaks in CdS microcrystallite systems. We have demonstrated that the main defects in the CdS-glass composites are cadmium vacancies, Vcd; and there are Vcd, Vs, Is and Scd defects in the CdS colloids. We expect that the nonlinear-optical properties of CdS microcrystallite systems are greàtly influenced by the excitons bound to these defects.
Group-velocity description of the arrival of the Brillouin precursor in a dispersive medium with absorption
Authors: Sherman George C. , Oughstun Kurt Edmund
Published: February 2023

The propagation of short pulses in a dispersive medium can be described in simple physical terms by employing the concept of the group velocity provided the medium is lossless. When the medium is absorbing, the group velocity description breaks down. In a previous paper,1 we presented a similar description employing the velocity of energy of monochromatic waves in place of the group velocity which is valid for a particular dispersive medium with absorption known as the Lorentz medium. That model describes the entire dynamics of the pulse as it propagates with the exception of the early stages of the evolution of the second precursor (otherwise known as the Brillouin precursor). Since that region contains the peak values of the pulse, it is important to include it in the model. The present paper describes the arrival of the Brillouin precursor in terms of the group velocity of a propagating field of the form exp [ωttω z] where ω and kω are real and positive.
Surface reflectances and human color constancy
Authors: Troost Jim M. , de Weert Charles M.
Published: February 2023

Robot-vision models of color constancy that are based on a linear approximation of illuminant and reflectance spectra are often generalized to the human visual system. Dannemiller's1 computational approach to color constancy is a good example. In this paper it is shown that such a procedure to estimate illuminant and reflectance spectra is less plausible for the human visual system than is implicitly assumed in robot-vision. The resemblance of the modeled hypothetical visual systems to the human visual system is misleading since it implies that surface reflectance is the illuminant-invariant object color descriptor the human visual system uses to achieve color constancy. However, an alternative type of descriptor is available that is not used to recover reflectance spectra. It has the advantage of allowing an interpretation that is preferable from the human point of view.
Coherent transient model of laser cooling in standing waves
Authors: DeVoe Ralph G.
Published: February 2023

Laser cooling in standing waves is related to the study of coherent optical transients. Transients in the u-component of the optical Bloch vector lead to a simple and unified physical picture of cooling at both low saturation parameter (optical molasses) and high saturation parameter (stimulated cooling). Optical molasses is shown to result from a free induction decay transient depending on the coherence relaxation time T2, while stimulated cooling is an incoherent effect of the population relaxation time T1. The sign, tuning, and saturation characteristics of each are attributed to specific transient phenomena. The model offers a bare-state physical picture of laser cooling which complements the dressed-state "Sisyphus" model. Phase-interrupting processes which make T2 < 2T1 reduce the trap potential by a factor of T2/2T1 and lead to a cooling force proportional to T2–2T1 which has not appeared in previous theories. The new term dominates both optical molasses and stimulated cooling when T2 «T1.
Resonance fluorescence of the quasi-continuum band
Authors: Sanchez-Villicaña V. , Sanchez-Mondragón J. J.
Published: February 2023

The dynamics of the Quasicontinuum band population with constant dipole strength distribution has been extensively studied. Revivals, population flopping and nonlinear population band distribution are known features, as well as the role played by each one of the relevant parameters.1 However, a more realistic approach requires abandoning the assumption of a constant dipole strength, the uniform level spacing distribution and near steady conditions. We carry on numerical simulations of the electron spectrum and the transient resonance fluorescence of a band with non-constant strength distribution, and discuss their time evolution, both linear and nonlinear populations, frequency distributions and their dependence on the band dipole distribution itself. We find that the distributions coincide in some specific cases with simple and straightforward approximations. This is qualitatively confirmed by analytical solutions in constant dipole strength case.
Numerical simulation of the Raman effect in birefringent optical fibers
Authors: Chen C.-J. , Menyuk C. R. , Islam M. N. , Stolen R. H.
Published: February 2023

In recent experiments by Islam, soliton switching in biréfringent optical fibers was demonstrated. In these experiments, solitons of about 300 fs were used, and the Raman effect played an important role in their evolution. We have derived the form that the Raman interaction will take in birefringent optical fibers.
A model of the quantum noise in the Stokes pulse energy spectrum from a transient-stimulated Raman generator
Authors: Walmsley Ian
Published: February 2023

Recently Swanson et al.1 have shown that, even in the transient regime of a Raman generator, when the Stokes pulses are nominally transform-limited, the mean frequency of the pulses fluctuates from pulse to pulse. The coherent modes model2 provides a simple, intuitive and computationally efficient method for determining the statistics of the Stokes light from a Raman generator. We use this model to calculate the probability density of the mean frequency of the Stokes pulse energy spectrum and show that it gives reasonable agreement with Swanson et al.'s experimental results. The spectral fluctuations in the transient regime arise because the excitation of high-order temporally coherent modes produces a time-dependent phase structure in the Stokes pulse. The phase of the Stokes field is more sensitive to the excitation of these high-order modes than is its amplitude, so that the pulse energy spectrum exhibits measurable fluctuations in the transient regime, even though the pulse temporal shape does not.3
Quantum-mechanical pointing fluctuations in stimulated Raman scattering
Authors: Kuo S. I. , Smithey D. T. , Raymer M. G. , Walmsley I. A.
Published: February 2023

We have observed fluctuations in the direction of propagation of light pulses generated by stimulated Raman scattering (SRS). This fluctuation is analogous to the pointing fluctuation of laser beams,1 and is due to quantum mechanical uncertainties in the occupation numbers of different spatial modes. When SRS is generated in an interaction region with Fresnel number less than unity, the lowest order spatial mode dominates the generation process, but higher order spatial modes are also weakly and randomly excited. This results in small fluctuations in the wavefront of the light field. The direction of propagation is characterized by the transverse component of an average wave-vector determined by the gradient of the wave-front. We report experimental results by measuring the "center of mass" of the far-field intensity pattern of a single Stokes beam, and the fringe separation of an interference pattern formed by superposing two independently generated Stokes pulses. The experimental results are compared to theory.2
Correlation effects in pump-depleted broadband Raman amplification
Authors: Bashkansky M. , Hilfer G. , Dexter J. , Reintjes J.
Published: February 2023

It has been predicted and observed that the gain in broadband stimulated Raman amplification depends on the pump-Stokes correlation.1 It was previously demonstrated that maximum Raman gain, equal to the single mode gain, was obtained when the pump and input Stokes were correlated. The width of the correlation peak was proportional to the inverse laser bandwidth. In most applications involving stimulated Raman scattering it is desirable to operate in the pump depletion regime for efficient conversion to the Stokes. It is therefore important to determine the degree to which the pump and input Stokes must be correlated under pump depletion conditions to obtain high pump conversion. We observe a maximum 70% pump depletion at a relative relay of zero between the pump and input Stokes. Conversion drops to 40% when pump and input Stokes are decorrelated. The width of the correlation peak is comparable to the inverse of the pump bandwidth. We will present data comparing results obtained for different laser bandwidths, for noncollinear geometries and for negligible pump depletion. We shall also present the results of numerical calculations that model our experiments.
A Laser Microbeam System for Gene Transfer Research
Authors: Shouhuan Zhou
Published: February 2023

A laser microbeam system has been build up, which generates a microbeam radiating the surface of cell and having a selfhealing hole on it. Through the hole the microbeam makes, the external flourescent substance and gene material get into its interior. We have successfully achieved an instant expression of Gus gene in tobacco pollen, with transfer rate as high as two percent. As for animal cells, DAPI-DNA transferred into cancer cells in human stomach.
Application of coherence theory to enhance backscatter
Authors: Rhodes William T. , Welch Gisele
Published: February 2023

Despite its relatively rare use in such problems, we have found that coherence theory explains the major phenomenon associated with enhanced backscatter (partial phase conjugation processes). Consider the case where a coherent wave field is scattered by a moving diffuser and then reflected back through the same diffuser by an ordinary mirror. Through the use of coherence theory we have shown that, to within a complex proportionality factor, the incident wave field can be inferred from coherence measurements made on the doubly scattered wave field. Specifically, the mutual intensity of the doubly scattered wave field is given by J12 = Jincoherent + Jcoherent. The first term corresponds to a spatially incoherent wave field of the kind that would be observed if the incident wave field were scattered by two different moving diffusers. In the far field this incoherent contribution produces an essentially uniform background intensity. The second term, on the other hand, corresponds to a wave field with exactly the same coherence properties as the incident coherent wave field. If the incident wave is a uniform plane wave, the doubly scattered wave field contribution corresponding to Jcoherent will in the time average focus to a point of light in the far field.
Second-order moments of the Wigner distribution function in first-order optical systems
Authors: Bastiaans Martin J.
Published: February 2023

Starting from the well-known description of a first-order optical system by means of its symplectic ABCD ray transformation matrix, a propagation law for the second-order moments of the Wigner distribution function is derived. A matrix is constructed from the second-order moments, which undergoes a similarity transformation when it propagates through a first-order system. This property leads to invariant expressions in terms of the second-order moments, based on the eigenvalues of the matrix mentioned before. Properties of these eigenvalues are derived. It is shown that, at least in the 1-D case, a relation similar to the well known bilinear relationship, which expresses the propagation of the curvature of a spherical wave through a first-order system, can be formulated in terms of the second-order moments. Finally, it is shown that in the higher-dimensional case such a relationship only holds when the second-order moments form a matrix that is symplectic, which is the case for a Gaussian signal, for example.
Stereopsis and kinetic depth: two sides of the same coin?
Authors: Blake Randolph , Nawrot Mark
Published: February 2023

Several lines of evidence indicate that stereoscopic information and motion information strongly interact to specify object shape and layout in depth. For example, adaptation to an unambiguous stereoscopic object temporarily stabilizes perception of an otherwise ambiguous kinetic (KD) display. In fact, stereoscopic adaptation can even create the perception of structure and depth in a display consisting entirely of dynamic random noise. Conversely, perceived depth in a KD display can bias depth segregation in a stereoscopic display. These and related findings have inspired a simple neural model that incorporates KD and disparity processing within a single network. The model comprises two levels: a layer of monocular directionally selective motion detectors that provide input to a second layer of disparity selective and direction selective binocular mechanisms. The network of facilitatory and inhibitory connections between binocular mechanisms promotes segregation of activity into separate neural pools specifying global motion in different depth planes. In the absence of disparity information, activity fluctuates in a manner mimicking the fluctuations in perception experienced when viewing a KD animation sequence. Unresolved questions include the role of head movements in modifying activity within the network.
Polarization-encoded optical shadow-casting: arithmetic logic unit design: parallel output generation
Authors: Ahmed James U. , Awwal Abdul Ahad S.
Published: February 2023

A polarization-encoded optical shadow-casting (POSC) system1 exploits the parallelism of optics to process 2-D coded input data in parallel. Previously, a multiprocessor1 was designed that was capable of generating both addition and subtraction results in parallel. The idea of this multiprocessor is extended in the current work, where an arithmetic logic unit, (ALU) capable of simultaneously generating sixteen logical operations of two variables and addition/subtraction results of three binary variables, is designed. To optimize the pixel size, the massive ALU truth table is partitioned2 and efficient minterm pairing is applied.1 The resulting coding of the inputs, and the space variant output1 decoding mask to detect the outputs in parallel are obtained using the POSC design algorithm.1 While operating as an ALU, all arithmetic output is generated in parallel, while eight logical outputs are generated in parallel by controlling the coding for C.
Nonlinear optical properties of a novel crosslinkable diazo-polymer
Authors: Eich M. , Kruger H. , Frank W. , Tschudi T.
Published: February 2023

Extending the novel method of preparing highly stable second-order nonlinear optical materials via thermally induced chemical crosslinking under electric field,1,2 we report the synthesis and characterization of a novel copolymer consisting of donor and acceptor substituted di-azogroups and glycidylmeth-acrylate (M
n
= 22000, M
w
= 48000). Due to the π-conjugation elongation, these NLO-moieties employ high µβ-values compared to their two-ring analogs. In contrast to the materials discussed in Refs. 1 and 2, this linear polymer can be solved and processed without any necessity of precrosslinking before poling. Films of a few microns thickness have been prepared by spin coating from a 20% solution in 1, 4-dioxan. The linear optical properties of the films were investigated by total internal reflection and absorption spectroscopy techniques. In situ corona poling and second-harmonic generation studies were performed on the samples using a fundamental wavelength of 1064 nm. The polar order was frozen by thermally induced crosslinking of the glycidyl groups. Measurement at elevated temperatures of 80°C showed no poling relaxation in the NLO signal.
Energy redistribution in molecules on the femtosecond timescale
Authors: Harris C. B. , Russell D. J. , Schultz K. E. , Zhang J. Z.
Published: February 2023

Liquid phase energy transfer has been studied in a range of molecules of varying complexity, providing a unique opportunity to compare various systems in solution. These systems include the recombination and relaxation of molecular iodine, the effect of solvent on the vibrational cooling of azulene, and the partitioning of energy in metal carbonyl fragments upon photodissociation. The iodine and azulene work, although performed in identical conditions, displays startling differences. The vibrational relaxation of molecular iodine is strongly dependent on solvent density and temperature, as predicted by isolated binary collision theories.1 The azulene relaxation rate is not strongly solvent dependent, yet it vibrationally relaxes much faster than molecular iodine.2 The vibrational cooling of Mn2(CO)10 photofragments occurs along two different pathways.3 Mn2(CO)9 relaxes through the CO stretch as well as through low frequency vibrational modes, while Mn(CO)5 relaxes only through low frequency modes, on a time scale similar to that seen in azulene. Thus IVR does not rapidly redistribute the excess energy in Mn2(CO)9 as it does in Mn(CO)5 and azulene.
Temporal and spatial correlation technique for rf moving phase grating
Authors: Yang Xuan-Min , Yi Ming , Zhu Li , Gan Jin-Fu , Yang Xuan-Min
Published: February 2023

Earlier works on investigating the imaging of rf moving phase gratinglike objects was more or less based on geometric optics, and the Doppler effects of moving objects were apparently ignored. Therefore the results were not satisfactory. A temporal and spatial correlation theory for imaging of rf moving phase gratinglike objects has been developed. A series of filtering techniques based on analysis of phases, amplitudes, and the temporal and spatial spectra has been established, and the highest visibility of image for rf moving phase objects has been obtained in experiments. The new theory and technique are useful for optical and acoustooptic (AO) signal processing. As a particular application, the ultrasonic progressing wavefront at the near field of an AO device has been visualized; it has two transducers either in or out of phase. It can be used to explain whether the beam steering theory for AO devices at the near field is correct.
Three-point joint density function for the intensity of a partially developed monochromatic laser speckle pattern
Authors: Rao Gudimetla V. S.
Published: February 2023

A three-point joint density function for the intensity of a partially developed laser speckle pattern is derived as an infinite summation of products of modified Bessel functions of the first kind. From this, a simpler expression for the corresponding density function of a fully developed (Gaussian) speckle pattern is developed. The results will be useful in obtaining the conditional density function of intensity for general optical scattering problems and to estimate the probability of error in signal to noise ratio calculations in optical systems such as optical radar.
Spontaneous spatial pattern formation in wide gain section lasers
Authors: Wenden S. G. , Jakobsen P. K. , Moloney J. V.
Published: February 2023

Two-level and Raman lasers with wide-gain sections undergo spontaneous symmetry breaking beyond the first laser threshold resulting in an off-axis emission that, if stable, would correspond to a ring in the far field. The angle subtended by the emission to the laser axis depends on the laser detuning, polarization decay time, and size of the laser cross-section. Optical vortices, propagating fronts, and complex spatio–temporal patterns are predicted to emerge at the first and second thresholds. The intensity dependent detuning and pump laser transverse profile in the Raman laser offers a fascinating array of pattern forming possibilities involving coexisting dark and bright waves. When the polarization decays much faster than the cavity field and medium inversion, one usually adiabatically eliminates this variable from the Maxwell-Bloch equations. Inclusion of transverse effects in this limit, however, leads to spurious transverse instabilities that can be mistaken for numerical grid oscillations. Decoupling of the polarization variable from the electric field allows arbitrarily high transverse wavenumbers to grow.
Cavity quantum electrodynamics with strong coupling in the optical domain
Authors: Rempe G. , Thompson R. J. , Brecha R. J. , Kimble H. J.
Published: February 2023

The radiative properties of atoms inside an optical cavity can be dramatically changed with respect to those in free space. In the strong-coupling limit, the reversible dipole interaction between an atom and the cavity field dominates the irreversible decay resulting from spontaneous emission and cavity damping. In this limit the atom and field can no longer be regarded as separate quantities but instead form a composite dynamic system. To enhance the dipole coupling constant and increase the photon storage time, our experiments are performed with a small cavity 1 mm long, with a finesse of 8 × 104. On average, 0.4 photons are sufficient to saturate the resonance transition at 852 nm for the cesium atoms used, while the cooperativity parameter for a single atom is 2. Optical bistability is studied in this system over the range 3 < N < 65 atoms inside the cavity, with the semiclassical theory predicting bistability for N > 5. We report observations of manifestly quantum effects in this regime, including photon antibunching and sub-Poissonian photon statistics, with the magnitude of these nonclassical effects observed to be largely independent of the number of intracavity atoms.
Mixed thermal-coherent revivals in the Jaynes-Cummings model
Authors: Kurmyshev E. V. , Sanchez-Mondragon J. J. , Arroyo-Correa G.
Published: February 2023

The existence of revivals in the atomic inversion of the Jaynes-Cummings model (JCM) has been pinpointed on the numerical display of its expectation value. However, until recently its individual identification, isolation, and analytical representation was successful if the initial photon statistics allowed the use of saddle point techniques. 1 The recent introduction of a new analytical method,2 free of such restriction, and its successful use with thermal JCM revivals allows us to study the mixed thermal coherent JCM revivals, drawing a direct relation to the saddle point technique. We compare our results with previous ones of the pure thermal case,2 and the coherent limiting cases, in particular with the systematic technique proposed by Fleischhauer and Schleich.
Crystal growth and optical characterization of a new nonlinear optical material: mixed methyl-(2-4-dinitro phenyl)-anniopanoate (MAP):2-methyl-4-nitroaniline
Authors: Rao S. M. , Batra A. K. , Lai R. B. , Loo B. H. , Metzger R. M. , Lee W. J.
Published: February 2023

A new nonlinear optical material formed by mixing methyl-(2-4-dinitrophenyl)-amino-propanoate (MAP): 2-methyl-4-nitroaniline (MNA) is grown from organic solutions. Details of the formation of the new material and its growth are given. The crystals are observed to belong to monoclinic space group P21. Preliminary structural data are given. Differential scaning calorimetric measurements show that it melts at 104.3°C. The SHG efficiency of the new material is observed to be close to that of MAP but much less than that of MNA. MNA has the largest second-harmonic coefficient reported so far. Since the new material crystallizes more readily in transparent rectangular prisms, the new material may be beneficial for devices. The optical absorption spectrum of the mixed crystal is studied in the range 500-2600 nm.
Response of the atmospheric sodium layer to short optical pulse excitation
Authors: Herman B. J. , Konopnicki M. J.
Published: February 2023

Some of the adaptive optics systems contemplated to ameliorate the effects of the atmospheric turbulence utilize guide stars. Guide stars are artificial beacons formed in the atmosphere by the interaction of a laser with matter in the atmosphere. Sodium guide stars are formed as a result of laser interaction with the sodium layer in the upper atmosphere. A small rf FEL is one of the candidates considered as a potential source capable of creating a sodium beacon. The pulse format of such a laser consists of trains of short optical pulses. The duration of an individual pulse is typically shorter than that of relevant relaxation times in the medium. The separation of the pulses may be longer or of the order of the relevant atomic memory time scale. To properly describe interactions of the atmospheric sodium layer with a laser characterized by such a pulse format one must utilize the optical Bloch equations (OBE). The OBE have been solved numerically using a simplified two-level model, and the resulting sodium layer response has been characterized. Additionally, an analytic solution has been obtained for the case in which both the population and coherence relaxation times are equal. The model is capable of providing useful insights.