bluuebunny/crossref_metadata_2025 huggingface dataset:
Alignment devices for ultrafast optics
Authors: MacFarlane Duncan L.
Published: February 2023

We describe two novel devices for optical beam alignment. One uses an elliptical mirror and a turning mirror to allow for a variable angle with a fixed position of incidence upon a sample. The other uses a parabolic mirror and a turning mirror to allow for a variable position with a fixed angle of incidence upon a sample. These devices have no chromatic dispersion, and the time of flight through either of these devices is a constant independent of the angle and position of incidence. Therefore, these devices are particularly useful for experiments and applications involving ultrashort pulses because the alignment of the beam on a sample under test can be adjusted continuously while preserving precise timing a requirement that might be imposed, for example, by a second pump beam of ultrashort pulses. Cascaded together, these devices allow placement of a laser beam upon a sample with arbitrary angle and position of incidence. Other combinations facilitate the capture of a signal beam by a detector in a measurement taken as a continuous function of the alignment parameters.
Frequency doubling of tunable solid-state lasers using lithium triborate crystal
Authors: Lin J. T. , Montgomery J. L. , Stalder M. , Lu Z. L.
Published: February 2023

Lithium triborate (LBO) is a newly discovered nonlinear crystal with features of high damage threshold, nonhygroscopic, wide angle bandwidth and may be noncritically phase-matched. In this paper we report the experimental and calculated results for frequency doubling of the tunable solid-state lasers of Ti:sapphire and Cr:LiSrAIf (LISAF) using LBO crystals angle cut 32.6 (in xy plane) and at 36 were used to cover the angle tuning ranges. In the case of Ti:sapphire laser, we have achieved 2.8% efficiency for the generation of 396 nm, where the fundamental beam at 792 nm, 30 ns, 90 mJ was focused by a 15-cm lens. We have measured the phase matching curves for 750-810 nm which agree very well with our calculated values. For the LISAF laser (0.8-0.96 μm), we achieved 20% doubling efficiency at an input energy of 30 mJ (pulse width of 50μs). The angular and spectral bandwidths of LBO were measured. Phase-matching angles for doubling 800-960 nm were measured and matched very well with the calculated values.
Temperature-insensitive phase-matched harmonic generation in deuterated L-arginine phosphate
Authors: Barker Charles E. , Eimerl David , Velsko Stephan
Published: February 2023

Deuterated L-arginine phosphate (dLAP) is a promising new crystal for frequency conversion of near-IR and visible lasers.1 Reported values of the thermal coefficients of refraction of dLAP predict the existence of a unique property: temperature-insensitive phase-matching directions for second-harmonic generation. We used a Nd:YAG laser to measure the thermal rates of change of phase-matching angles in the principal dielectric planes of dLAP. For the type I phase-matching locus, we have found that the phase-matching angle relative to the alpha axis increases at a rate of 248 μrad/°C in the alpha-beta plane and decreases at a rate of 38.3 μrad/°C in the alpha-gamma plane, whereas for the type II phase-matching locus, the phase-matching angle increases at a rate of 237 μrad/°C in the alpha-beta plane and increases at a rate of 30.9 μrad/°C in the alpha-gamma plane. The opposite signs of the thermal rates of change of the type I phase-matching angles verify the existence of temperature-insensitive phase-matching directions in the type I second-harmonic generation phase-matching locus. Discrepancies between the predicted and measured thermal behavior of the dLAP phase-matching loci are attributed to errors in the reported values of the thermal coefficients of refraction.
Space variance in optical-sectioning microscopy
Authors: Sitter David N. , Rhodes William T.
Published: February 2023

In optical-sectioning microscopy, the blur ring from out-of-focus object structures is generally assumed to be space invariant. In fact, the slight change in magnification produced by defocus and the finite Fresnel number of the microscope cause the blurring to be slightly space-variant and asymmetric about the in-focus plane. We present an accurate model that accounts for the space variance and asymmetry. The model is simple and describes the blurring from each out-of-focus object plane by a scaling operation followed by a convolution.
Observation of quantum features in the evolution of a Rydberg wave packet
Authors: Yeazell John A. , Stroud C. R.
Published: February 2023

Quantum mechanical wave packet states can approach the classical ideal of a spatially localized particle traveling along a well-defined trajectory. These states offer a system in which the classical limit of quantum atomic theory can be studied. In this work, a wave packet that is radially localized and whose radial motion occurs at the classical orbital period is studied. Despite these strong classical features, the long-term evolution displays the quantum nature of the state. As the wave packet evolves, it becomes dispersed, and the radial motion becomes irregular. However, the wave packet does not remain dispersed, and classical motion returns with the return of the spatial localization. Both the collapse and revival of the wave packet occur because of the quantized nature of the atom. In this experiment, the wave packet was excited to the Rydberg slates by a short, ultraviolet pulse from the ground state of potassium. The probe pulse delay was scanned, and the resulting photo-ionization signal displayed the evolution of the wave packet. The collapse and revival of the radial wave packet were observed.1
Atomic excitation by a pulse train I: two-level atoms
Authors: Bradley Lee C.
Published: February 2023

An assembly of ground-state two-level atoms with a Maxwellian velocity distribution is considered to be illuminated by a near-resonant train of Gaussian pulses whose pulse separation is of the same order of magnitude as the natural decay time of the upper state by spontaneous emission. The equations of motion of the density matrix, including spontaneous decay, are numerically integrated over the duration of one pulse and are analytically integrated between pulses. In this way, the transition matrix is derived. The time evolution of the system is then followed by successive multiplications of the state vector by the transition matrix. Steady state is attained after a few pulses. Because the pulse train has side bands separated by the pulse repetition frequency, corresponding velocity groups are preferentially excited. The response (defined as the time-average spontaneous emission of the assembly) is found to be a quasi-sinusoidal function of the number of Rabi flops per pulse. Frequency modulation of the pulse train leads to smaller variation in the response and, consequently, to considerably higher response.
Atomic dynamics in a two-photon process
Authors: Cardimona D. A. , Kovanis Vassilios , Sharma M. P.
Published: February 2023

We investigate the atomic inversion dynamics that occur when an atom interacts with a two-mode quantized radiation field. Our work uses Schrodinger theory with the rotating wave approximation. We adiabatically eliminate all but two of the atomic states in order to obtain analytical and numerical results. By varying the width and average photon number of the field statistics, we have uncovered secondary revivals that arise because of the complicated double sum over the two field modes in the population inversion. The diagonal part of the sum (the part that contains commensurate frequencies) is closely related to the degenerate-mode work of Buck and Sukumar.1 The breaking of the exact periodicity with secondary revivals and eventual erratic behavior result from the off-diagonal terms. Use of Poisson statistics allows exact analytic results to be obtained and also allows comparisons with previous work to be made. However, because the width and mean are intimately related for Poisson statistics, we also use Gaussian statistics so that their effects may be separated. To investigate various possible initial field conditions, we use squeezed states (oscillatory in photon number), displaced number states, and generalized states. The latter interpolate between number states, coherent states, and thermal states.
Apparent contrast of a phase-reversed stabilized image
Authors: Tulunay-Keesey U. , Saleh Bahaa E.A. , VerHoeve James N.
Published: February 2023

The faded image of a high-contrast stabilized target reappears if a brief step increment of uniform luminance is added to the target, but the regenerated apparent image is reported to be of the opposite phase of the target. Using a matching technique, we measured the contrast of the apparent image as a function of the magnitude of the uniform increment for several luminances and two contrasts of the adapting target. It increased linearly with the magnitude of the increment and was an exponential function of the adapting background luminance. When the increment was a fixed proportion of the adapting background, the apparent contrast was constant with respect to the background luminance. The shapes of the functions relating the uniform increment to the adapting back ground remained the same, but they were scaled when contrast was increased. These results indicate the presence of an adaptation process that multiplies the inverse sensitivity or gain image by the incremented target to produce an apparent phase reversal. They are consistent with a model in which gain is a decreasing function of target luminance.
Flash masking by nearby luminance noise
Authors: Cohn Theodore E. , MacLeod Donald I. A.
Published: February 2023

We have measured light-adapted foveal luminance increment thresholds for 1.5 ft. (46 cm) diameter white targets by using a staircase. We wished to learn more about the mechanism that signals foveal luminance change. When identical luminance noise is placed at two spots 1.5 ft. (46 cm) to each side of the test, the threshold is more than doubled. The detection mechanism has a relatively broad field because the noise locus must be moved more than 5 ft. (1.5 m) away from the test for its effect to disappear. The mechanism may be even-symmetric but it cannot be linear, nor can scattered light explain the result, because antiphase noise modulation of the two flanking spots is at least as effective as in-phase noise. A rectifying nonlinearity is possible, but that cannot be the entire explanation because the antiphase noise is more effective than in-phase noise at low and medium separations. Similarly, in subthreshold summation tests, opposite-polarity flank pulses are at least as helpful as same-polarity flanks. One intriguing hypothesis is that the mechanism detecting our test stimulus is motion-sensitive and that the antiphase noise is effective within that mechanism because it simulates motion across the field containing the test. Indeed, subjective motion due to the noise mask is apparent to our observers.
Nonlinearities in flicker electroretinograms
Authors: Burns Stephen A. , Elsner Ann E. , Johnson Mary A. , Sevems Matthew L. , Kreitz Mark R.
Published: February 2023

The electroretinogram (ERG) is the mass electrical response of the retina to light and is affected by a wide variety of diseases. Because there are many retinal cell types contributing to the electrical response, dissection of the locus of disease-induced abnormalities is qualitative at best. We are using high temporal frequencies to minimize the contributions of rods and non-neural retinal cells to the ERG response. We Fourier-analyze the ERG responses to light modulated by either a sinusoidal or complex temporal waveform and use the amplitude of the linearand nonlinear components of the response to measure early visual processing. For instance, analysis of the beat amplitude in a two-sine-wave technique reveals a mechanism, probably the photoreceptors, that is low-pass with a 3 dB point at 50 Hz and a high-frequency slope of 4.0 on a log-log plot. Analysis of second- and higher- order nonlinear responses reveals a similar high frequency slope but a complex dependence of response amplitude on frequency. The data are compatible with generation by an essential nonlinearity, possibly a nonlinear gain-control mechanism with a temporal delay. We will illustrate the clinical utility of our approach with data from patients with either glaucoma or central retinal vein occlusions.
Temporal integration of equiluminous color in megalopapilla and hypoplasia
Authors: Billock Vincent A. , Grigsby Scott S. , King-Smith P. Ewen
Published: February 2023

In subjects without optic nerve defects, asymmetries in the detection thresholds of equiluminous opponent colors are rare. King-Smith et al.1 reported four subjects whose detection thresholds violated the symmetry found in normal subjects. Two had acquired retinal defects: one had a microinfarct of the optic nerve, and the other had Leber's optic atrophy; in both cases only the blue-yellow system had an asymmetry. The other two subjects appeared to be normal, but we later discovered that they have mild congenital optic nerve defects. One of these subjects has megalopapilla (abnormally large optic discs), and the other has optic nerve hypoplasia (abnormally small optic discs). The subject with megalopapilla has much higher thresholds for blue than for yellow. The variation of threshold as a function of duration is steeper than Bloch's law predicts for blue but not for yellow. The asymmetry is maximum at approximately 5° parafoveal. The hypoplastic subject was found to have large detection-threshold asymmetries for both red-green and blue-yellow equiluminous spots. Critical durations for equiluminous red were significantly longer than for green, relative to normal subjects. Violations of Bloch's law were also seen for this subject. Spatial and temporal contrast sensitivity for both subjects were within normal limits.
Saturation of scintillation effects on the Cn2, I0, heat, and momentum fluxes scintillometer
Authors: Hill Reginald J. , Ochs Gerard R.
Published: February 2023

An optical scintillometer has recently been developed to measure Cn2, I0, and the surface fluxes of heat and momentum. This scintillometer uses a diverged HeNe laser beam received through a 1 mm aperture and, on the same path, a 4.4 cm diameter incoherently illuminated aperture with a 4.4 cm diameter receiver aperture. Because of the wide dynamic range of atmospheric turbulence and the need for an unattended, reliable scintillometer, both received signals are logarithmically amplified. Two such scintillometers were operated simultaneously, one on a 500 m path so that strong scintillations are observed, and another on a 150 m path in the center of the longer path so that Cn2 and Io could be obtained with weak scintillation approximations. This operation provides all the parameters needed to compare the data with theory, because the experiment site is horizontally homogeneous. The laser-beam scintillation from the 500 m path is compared with the heuristic theory for log-amplitude scintillation. The large-aperture data is compared with the first-term asymptotic theory for strong scintillations of a spatially extended incoherent source. It is found that the effects of saturation can be corrected, and the values of Cn2, Io, and heat momentum fluxes can be obtained, even for such long paths and strong scintillations.
Radiative transfer in random inhomogeneous media
Authors: Cairns Brian
Published: February 2023

Radiative transfer in random inhomogeneous media has been considered by a number of authors. The most detailed treatments pertain to radiative transfer in the small-angle scattering approximation. I use a local-perturbation method1 to obtain an equation for the transfer of the mean specific intensity in media in which the small-angle scattering approximation is not valid. My method assumes that the fraction of radiation is scattered or absorbed over a correlation length of the random medium is small compared with the fraction that propagates undisturbed through the same distance. With this assumption my equation for the transfer of the mean specific intensity takes the same form as that of the usual radiative transfer theory, with extinction and scattering coefficients that are determined by both the first- and the second-order statistics of the fluctuating medium. For particular problems the mean specific intensity can be calculated by using the standard numerical techniques that are employed in radiative transfer theory. The local perturbation method that I use can also be applied to the derivation of equations for the propagation of higher-order moments of the specific intensity in random media that do not satisfy the small-angle scattering approximation.
Recommendations concerning optoelectronics education
Authors: Cathey Thomas
Published: February 2023

The recommendations of 35 colleges and universities and people in industry concerning optoelectronic education, what is needed, and how the needs can be met are reported.
Two inverse problems in spectroscopy with partially coherent sources and the scaling law
Authors: Wolf Emil
Published: February 2023

In an interesting recent paper Martinez-Herrero and Mejias established new existence theorems regarding the uniqueness of solutions to inverse problems involving homogeneous sources.1 In my pa per some of the theorems are generalized to planar, secondary, quasi-homogeneous2 sources, and explicit solutions are presented to two inversion problems with sources of this class, assuming that their normalized spectra are the same at each source point. I show that if the high spatial-frequency components of the degree of spatial coherence may be neglected, the far-zone spectrum of the emitted light uniquely determines both the normalized source spectrum and the degree of coherence of the source. It also follows from this analysis that the scaling law,3 previously derived as a sufficiency condition, is also a necessary condition for spectral invariance on propagation.
Classical analysis of the Franson two-photon correlation experiment
Authors: Ou Z. Y. , Mandel L.
Published: February 2023

A two-photon correlation experiment of the kind that was proposed by Franson and has recently been carried out by two groups is analyzed. In this experiment two simultaneously produced photons are directed along two paths to two photodetectors without mixing. An unbalanced interferometer with delay time that is much longer than the coherence time of the light is inserted in each path. Yet the rate of two-photon detection by the two detectors in coincidence exhibits interference as the path difference is changed. The question of whether classical field theory can account for these observations is discussed. We show that no ergodic classical field is able to reproduce the experimental results, although a nonergodic field can give rise to interference through the artifice of generating an ensemble by initializing repeatedly.
Comparison of scalar diffraction theory and electromagnetic theory solutions to binary conducting gratings
Authors: Gremaux Douglas A. , Gallagher Neal C.
Published: February 2023

We compare solutions to the problem of electromagnetic wave scattering by perfectly conducting, rectangular grooved gratings by using several scalar theories and several vector theories. The period of the gratings is on the order of the wavelength. Parameters of the grating, such as the width and depth of the grooves and the period, are varied with respect to the wavelength. The angles of incidence of the incoming plane wave are also varied. As these parameters are changed, the magnitude and phase of the diffracted orders calculated from the scalar approach are compared against the electromagnetic solution. The purpose of this comparison is to determine the range of validity for the scalar solution. For geometries where the scalar solution is poor, it may be possible to determine correction factors to improve it. Insight gained from this study may be applicable to the analysis of more complex gratings and grating-like structures.
Multiple scattering by a planar array of parallel dielectric cylinders
Authors: Bever Steven J. , Allebach Jan P.
Published: February 2023

We are engaged in a research effort to design modulated ribbon gratings that are composed of a number of parallel, dielectric cylinders joined by flat sections of dielectric material. As an important first step in this work, we have solved for the multiply scattered field from a planar array of N parallel dielectric cylinders. The multiple-scattering model takes into account all contributions to the excitation of a particular cylinder by the radiation scattered from the remaining cylinders. A common approach to calculating the field scattered by two or more parallel cylinders is to express the multiple-scattering linear equations in matrix form and then to solve the matrix expression for the multiple scattering coefficients by iterative refinement or matrix inversion. However, when the expansion of the matrix expression is divergent, the iterative refinement method is also divergent. In addition, the matrix inversion approach fails for ill-conditioned matrices.
Iterative discrete on-axis encoding of diffractive optical elements
Authors: Welch W. Hudson , Feldman Michael R.
Published: February 2023

The recently developed iterative discrete on-axis (IDO) encoding method (based on iterative optimization routines such as simulated annealing) has previously been used to generate arrays of signal spots with extremely high diffraction.1 This encoding method has been extended to encode diffractive optical elements for high-resolution imaging. The encoding method is used to determine the location of the fringes in the computer-generated hologram (CGH) in order to minimize a particular cost function. Depending on the cost function, the CGH can be designed to minimize aberrations, maximize diffraction efficiency, and/or minimize noise due to undesired diffraction orders. These design parameters can be optimized for several points in the output plane and for a range of wavelengths. Standard diffractive element design procedure consists of two steps: (1) use of simulated annealing to calculate the desired continuous-phase function of the CGH, and (2) use of a deterministic encoding method to convert the phase function to a set of discrete, quantized fringes of constant phase. The modified IDO encoding method differs from the standard procedure in that the set of fringes are calculated directly by simulated annealing. The computation time can be decreased by restricting the hologram transmittance to contain particular symmetries (e.g., radial symmetry). Computer simulation results indicate that our method can produce diffractive optical elements with higher diffraction efficiency and larger minimum feature sizes than can conventional encoding methods. Experimental results will be presented.
Demonstration of a monolithic grating surface-emitting laser master oscillator-cascaded power amplifier array
Authors: Abeles J. H. , Carlson N. W. , Bour D. P. , Liew S. K. , Lin P. S. D. , Gozdz A. S.
Published: February 2023

Monolithically integrated master oscillator-power amplifiers using grating surface-emitting lasers have been fabricated using first-, second-, and nonintegral-order gratings defined by electron-beam lithography. The device consists of one master oscillator and three cascaded traveling-wave amplifiers with associated output coupling gratings. Device performance will be reviewed.
Generation of high peak power, subpicosecond pulses from a semiconductor diode laser
Authors: Delfyett P. J. , Lee C. H. , Florez L. , Stoffel N. , Gmitter T. , Andreadakis N. , Alphonse G. , Connolly J.
Published: February 2023

Compact and efficient sources of high repetition rate, high peak power optical pulses are needed to replace the standard ultrashort optical pulse generation schemes due to their relatively large size and poor wall plug efficiency. In this paper, we present a new hybrid node-locked semiconductor laser system which is capable of producing optical pulses of 0.56 psec in duration with peak powers in excess of 38 watts. These optical pulses are both the shortest and most intense ever produced from an all semiconductor laser diode system. The optical pulses were generated by forming a hybrid mode-locked external cavity semiconductor laser, which incorporates a semiconductor traveling wave amplifier (TWA) as the gain medium, and a multiple quantum well (MQW) saturable absorber. Hybrid mode locking is achieved by actively mode locking the laser using current modulation techniques and tuning the laser operating wavelength to lie within the excitonic absorbtion region of the MQW saturable absorber. The generated optical pulses were compressed utilizing a grating pair compressor to remove the chirp which is impressed upon the optical pulse during the mode locking operation of the oscillator. The typical pulse duration generated directly from the oscillator is ~ 5 psec; the pulse durations obtained after compression were 0.56 psec. In order to achieve high peak output power, the resultant compressed pulses were reamplified in a semiconductor traveling wave amplifier. The resulting peak power obtained after amplification was 38 watts. In addition, we have measured the timing jitter of the laser system for pure passive mode locking and for hybrid mode-locked operation. We have observed that the hybrid mode-locked laser system has much less phase noise than the passively mode-locked laser.
Longitudinal mode control in multisection laterally-coupled-cavity semiconductor lasers
Authors: Griffel G. , Nabiev R. , Marshall W. K. , Grave I. , Yariv A.
Published: February 2023

We have demonstrated frequency selectivity and single-longitudinal-mode operation in a multisection gain-guided laterally-coupled-cavity (LC2) semiconductor laser. The device consists of two strongly coupled stripe lasers, each having two electrodes. The longer (~400 mm) served as a gain-section electrode and was forward biased, and the shorter (50100 mm) was reverse-biased and therefore provided an absorbing section. The absorbing-section electrodes of the two lateral elements were located at opposite ends of the device. By choosing the length and adjusting the reverse voltage of these sections, we could vary the magnitude and the phase of the reflectivity at each end. A detailed round-trip analysis showed that such a device should exhibit a periodic frequency dependence of the mode threshold gain. The fine details of this periodic behavior depended on the operating conditions and could be controlled. In the experiment isolated equispaced longitudinal-mode-operation was demonstrated. The frequency of these modes could be tuned by varying the absorbing section voltages. The operating conditions could be easily set for a single-longitudinal-mode operation.
Modeling quantum effects in reduced-dimensionality structures for optoelectronic devices
Authors: Schulman Joel N.
Published: February 2023

Optoelectronic devices made from ultrathin semiconductor layers make use of novel quantum-mechanical effects that are produced by electron confinement. Understanding these effects and using them for device application requires solving Schrodinger's equation in the simplest approximation compatible with the phenomenon under consideration. I will review models for calculating the optical and electronic properties of various systems, including quantum wells, resonant tunneling structures, quantum wires, and strained heterostructures. Comparison of the models will be made in the context of one-band, two-band, and multiband approximations. Issues such as optical selection rules and oscillator strengths, type I versus type II heterosystems, direct and indirect band gaps, effective mass tailoring, non-parabolicbands, valence-band mixing, as well as issues of practical computer implementations, will be discussed.
Carrier recombination rates in GaAs and InGaAs quantum-well lasers
Authors: Chen Y. C. , Waters R. G. , Coleman J. J. , Bour D. P. , Wang P.
Published: February 2023

The carrier recombination rates in GaAs1 and strained InGaAs/GaAs single-quantumwell lasers have been studied using the differential carrier-lifetime technique for carrier densities from 1017-1019/cm3. We have found that the carrier lifetime is not an intrinsic property of the material but is strongly structure-dependent. Under high levels of excitation, the recombination rates deviate considerably from the recombination rules of the bulk materials. The rates are typically smaller in quantum wells that have lower potential barriers and/or thinner well widths. The rates increase sublinearly with increasing carrier density up to carrier densities of approximately 1017/cm3 (rather than super-linearly as is observed in the bulk), but they remain nearly constant for densities greater than 1019/cm3. This occurs because a portion of the injected carriers populate the continuum states of the confinement layers where the carrier volume density is diluted and the overall carrier lifetime is prolonged. These inactive carriers may lead to the anomalously large linewidth enhancement factor in some InGaAs/GaAs lasers. Our experimental work also demonstrates that Auger recombination is negligible in GaAs and strained InGaAs/GaAs single quantum wells for carrier densities on the order of 1019/cm3.
Minimum-uncertainty states for amplitude-squared squeezing
Authors: Bergou Janos , Hillery Mark , Yu Daoqi
Published: February 2023

Normal squeezing is described in terms of variables which are linear in the field creation and annihilation operators. Amplitude-squared squeezing, on the other hand, is defined in terms of variables which are quadratic in these operators. As a result processes, such as second-harmonic generation, which couple one mode amplitude to the square of another convert this kind of squeezing into normal squeezing. In particular, the variables one considers are the hermitian part and one over i times the antihermitian part of the square of the annihilation operator. The variances of these observables obey an uncertainty relation. In order to better understand the properties of amplitude-squared squeezing it is useful to find the minimum uncertainty states corresponding to this uncertainty relation. These states are described by two parameters; the first,, gives the expectation of the square of the annihilation operator and the other λ, describes the amount of amplitude-squared squeezing. AH of these states have a mean amplitude of zero. These states for which =0 have unusual noise properties in that their Q functions have a four-fold rotational symmetry. We also find that a squeezed vacuum state is an amplitude-squared minimum uncertainty state.
Time-resolved fluorescence kinetics from benign and malignant tumors
Authors: Pradhan Asima , Tang C. C. , Alfano R. R. , Cleary J. , Prudente R. , Celmer E.
Published: February 2023

We have measured fluorescence kinetics from benign tumor tissues and cancerous human breast tissues. The samples were excited with the third-harmonic, 353 nm, 5 ps pulse of a mode-locked Nd glass laser with 30 mJ of energy. We measured the fluorescence lifetimes at different wavelengths using a streak camera with 10 ps resolution. The results display double-exponential fluorescence decay profiles. It appears that the fast component of the decay in the malignant tumors is faster (û ps) than that of the benign tumors (200 ps). The slow component of the decay from malignant tumors was slower (2.4 ns) than that of the benign tumors ( ns). The faster fast component of malignant tumor implies more nonradiative processes. These preliminary results indicate that benign tumors can be distinguished from malignant tumors.
Dynamic effects of focusing in an all-optical passive driven system
Authors: Jones D. J. , Bandy D. K.
Published: February 2023

By incorporating the radial dependence of the field, we explore the dynamical behavior of a passive optical system consisting of two focusing lenses, optically thin passive medium, and two partially transmitting mirrors, where one mirror functions as the entrance port for the external signal, and the second functions as the output coupler. The medium and the free-space diffraction are described by the Maxwell-Bloch equations and Kirchhoff's diffraction integral, respectively. A comparison between confocal resonators and nonconfocal resonators is made, and polarization effects are isolated.
Stable operation of a powerful 3-Hz line-tunable TEA-CO2 oscillator-amplifier system
Authors: Decker Jennifer E. , Lagacé Simon , Bérubé Jean , Beaudoin Yves , Chin See Leang
Published: February 2023

We report a medium-repetition-rate, highpeak-power CO2 oscillatoramplifier chain producing 10.6 m pulses of up to 1014 W/cm2 for use in intense-laser-interaction experiments. It has a simple provision for reducing retroreflections. Parasitic oscillation and amplified back reflections are deleterious phenomena often associated with high gain laser amplifier chains. Because the gain duration of atmospheric amplifiers is relatively long, a long optical delay (about 50 m or more) is installed to reduce the amplifier gain before any back-reflected energy maybe amplified.1 Electro-optic crystals, plasma switches, or saturable absorber gas are often used to isolate the reflection. The latter method is the simplest. It depends on the relaxation time of the gas. A popular choice of SF6/He is not sufficient. We found that SF6:C2H6::5:760 mixture takes only 11 ns to relax.2 Situating such a saturable absorber cell in the amplification chain, therefore, substantially reduces amplified retroreflections without the need for high pressure gain modules or optical delays, and it simultaneously provides contrast enhancement. Our laser now routinely operates at 3 Hz, 1 ns, and 1 J/pulse for experiments on tunnel ionization of atoms and molecules.
A simple model of laser without inversion
Authors: Ru P. , Narducci L. M. , Scully M. O. , Keitel C.
Published: February 2023

The emergence of laser action from an atomic system without population inversion is beginning to attract theoretical and experimental attention as a possible way of generating useful coherent radiation at unusual wavelengths. The goal of this communication is to clarify the physical origin of this phenomenon using a four-level system whose ground state consists of two quasidegenerate levels that are coupled to a higher-lying state by a Raman-like transition. In the presence of the ground-state coherence induced by the Raman field, we calculate the absorption spectrum of a weak probe whose tunable frequency scans across the transition frequencies between the two ground-state levels and another higher-lying state that may or may not be weakly excited by an incoherent pump mechanism. Our calculation, based on a dressed atomic state approach, clarifies the conditions that must be satisfied to produce gain, identifies the frequency (or frequencies) at which the gain is maximum, and elucidates the functions of the incoherent pump, the Raman field, and the coherence between the ground-state levels in this process. An appropriate set of Maxwell- Bloch equations for a ring-cavity model of this system confirms the appearance of laser action when the small-signal gain conditions are satisfied.
Designing continuous dataflow optical computing systems: I. synchronization
Authors: Heuring Vincent P. , Pratt Jonathan P.
Published: February 2023

Some optical computer architectures and subsystems employ continuous dataflow designs, rather than inherently slower designs that employ latching components, in order to speed information flow. This class of design relies on precise synchronization of signals at all times and at all locations in the machine in order to ensure correct.
Correlation-induced spectral changes in homogeneous and inhomogeneous media
Authors: Gamliel Avshalom , Agrawal Govind P.
Published: February 2023

It was recently shown that the spectrum of partially coherent light can change on propagation.1 So far most of the work has applied to propagation in free space and has been limited to far-zone observation points. In this paper we consider the propagation of partially coherent light through homogeneous and inhomogeneous media. Our formulation is based on the analysis of Agrawal et al.,2 which applies to graded-index fibers whose index of refraction changes quadratically as a function of the radial distance from the core center. With this formulation we derive expressions by using the paraxial approximation for the spectrum of the field for arbitrary propagation distances. This allows us to examine the evolution of spectral changes as a function of the propagation distance and the state of coherence of the source. The results for propagation in free space and in homogeneous media are derived by using the appropriate limits. The effects of chromatic dispersion are also investigated by allowing the refractive index to be frequency-dependent.
A Fourier-transform spectrometer for the visible and UV region based on laser-diode interferometric control
Authors: Wyntjes Geert , Engel James , Carlson David , Dorval Rick
Published: February 2023

We describe the design and preliminary performance of a Fourier transform spectrometer (FTS) built to operate in both the visible and UV regions. Conventional FTS instruments have generally been restricted to use in the IR because of the difficulties in providing sufficiently precise control of the mirror velocity and alignment. We are building an FTS, which uses a laser-diode source, in which both mirror motion and alignment are dynamically controlled on the basis of interferometric signals. By using a multi-phase detection technique, we are able to make interferometric measurements with /768 precision at a 5 MHz update rate. These data are used to servocontrol the mirror velocity and alignment to better than 0.01% and 1 radian respectively. This degree of control, combined with optics that are good to /40 in the visible-light spectrum, make it possible to attain spectral resolution in the visible and near-UV regions that is limited only by radiometric noise considerations.
An all-fiber tunable coupler and switch
Authors: El-Sherif M. A. , Herczfeld P. R. , Bobb L. C. , Dunn S. C. , Stephens S. H. , Sullivan E. J.
Published: February 2023

Photonic couplers and switches, used in communication systems, are based on integrated optic devices. These devices are actually miniature interferometers and have a polarization sensitivity. To eliminate these limitation factors and insertion losses, it has been natural to examine the possible uses of the fiber links for coupling and switching of the optical signals. Coupling between adjacent fibers can be controlled by replacing the cladding with an active material and applying an external field to this modified region. The principle of using an active modified cladding to control the propagation characteristics within the fiber core has been discussed in previous work.1,2 In this paper, we present a novel structure of an all-fiber tunable coupler and switch. This is accomplished by twisting two uncladded sections of adjacent fibers together and using an electro-optic material as an active modified cladding. When the structure is exposed to an electromagnetic field, the index of refraction of the active material varies. This change in the boundary conditions of the fibers results in a change in the coupling coefficient between the twisted fibers. A device has been fabricated in which a nematic liquid crystal is employed as the electro-optic cladding. The response of the device to the external fields shows precise control of the coupling coefficient. Ferroelectric liquid crystals and solid electro-optic materials can be used for high-speed switching. This structure presents a new class of all-fiber devices and can be used in modulation and sensor applications.
Chromatic aberration and calibration of the receptor array
Authors: Knoblauch Kenneth , Maloney Laurence T.
Published: February 2023

Although most models of the eye predict the presence of chromatic aberration, colored fringes are not typically seen at the edges of objects. Luminance transients introduced by transverse chromatic aberration (TCA) of the eye were computed, using a reduced eye model (Thibos, 1987), for thin vertical lines equiluminant with a background. The spectral distributions used were typical of phosphors from a television screen; the lines were presented off-axis. The transients produced were incremental and decremental perturbations on each side of the lines and were sufficiently large to be expected to be visible. The largest transients occurred for conditions that included the R phosphor, probably because of its narrow-band peak at approximately around 620 nm. If the spatial distribution of receptor excitation is examined instead, the problem becomes one of determining how the different receptor classes calibrate the location of their images. We examined the spatial distribution of receptor excitation that results from TCA for rods and the three cone types for several lighting models and derived sufficient conditions for an adaptive algorithm to reduce or eliminate the effect of TCA.
Effect of the warning signal on visual reaction time during recovery from general anesthesia
Authors: Letourneau J. E.
Published: February 2023

The purpose of the study was to measure recovery from general anesthesia. A group of 23 patients underwent surgery under general anesthesia with enflurane (N = 21) or halothane (N = 2). Anesthesia lasted 25120 min (mean = 52 min). Patients were measured before induction of anesthesia (trial 1) and 1, 2 and 3 h later (trials 2, 3, and 4). A control group (N = 23) underwent the same procedure. The instrument measured subjects' reaction times to a green light. A white light preceded the onset of the stimulus light. The foreperiod lasted successively 3, 2, and 4 s in each of three trials. Reaction time was longer (F = 5.09, p) on trials 2 and 3; patients reached the baseline level (t = 0.94) on trial 4. The performance of the control group was constant within an equivalent length of time (F = 0.62). The same experiment was repeated in order to compare the effects of a visual warning signal (VWS) and an auditory warning signal (AWS). Anesthesia was maintained with isoflurane (N = 18) or enflurane (N = 12). A buzzer (AWS) or a white light (VWS) was heard or seen at a distance of 1 m. Conditions were counterbalanced. The differences between the four trials were significant when patients were submitted to an AWS (F3, 119 = 17.06, p) or a VWS (F3, 119 = 25.87, p). The differences between reaction times with an AWS and those with a VWS were significant on the four trials. Reaction time was systematically shorter with an AWS than with a VWS and yielded a biased measure of recovery from general anesthesia.
Three-dimensional camera and rangefinder for ocean-surface imaging
Authors: Puerta Antonio Medina
Published: February 2023

Jet Propulsion Laboratory is developing a rangefinder camera system for the study of ocean waves. The system can be used as a real-time, three-dimensional television camera for general application. We have conducted an analytical study of the system to establish a theoretical framework and to determine the optimum parameters for recording ocean wave information. We are building an operating prototype based on theoretical work. Techniques have been developed to measure the arbitrary shape of a surface using "time of flight" and modulated laser systems. Our system uses a modulated laser, but no scanning is required. Instead, a charge-coupled device (CCD) camera performs the spatial sorting of picture elements, thus simplifying the system considerably. The imaged scene is illuminated with pulses of light generated with a Nd:YAG laser or simply with a flash lamp. The camera is electronically shuttered at the pulse rate. This way, a simple synchronous, or homodyne, detection of phase is accomplished. The phase of the modulated light reflected from each object picture element is proportional to its distance and to the number of collected electrons in that pixel. Our images of the ocean surface locate specular reflections three-dimensionally. We find that it is possible to recover a three-dimensional surface from specularities.
UV transmittance and optical homogeneity of synthetic fused silica—Dynasil
Authors: Vaynerman Vladimir
Published: February 2023

Synthetic fused silica, Dynasil, is widely used in modern optics because of its special optical characteristics is widely. UV transmittance and optical homogeneity are two of its most important qualities. A study of UV transmittance has resulted in determination of the distribution of that characteristic in the manufactured boules. The profile of the area in the boules where UV transmittance exceeds 80% (for 185 nm wave length and 10 mm sample thickness) has been determined, and strict quality-assurance procedures have been implemented. The accuracy of optical homogeneity measurement performed on fine ground silica blanks (oil-on-plate technique) with ZYGO MarkII ZAPP interferometer has been studied. The systematic error of the measurement (bias) was found to be 1/30 of a wavelength for a 4 in. (10.16 cm) aperture and 1/15 of a wavelength for 12 in. (30.48 cm) aperture; the data scatter was about 30% of the bias value.
Optical novelty filter demonstration for museum exhibition
Authors: Lininger D. M. , Hebler V. , Anderson D. Z.
Published: February 2023

An optical novelty filter1–3 detects changes in a scene. To illustrate the idea, imagine a still-life mountain scene as the input pattern. Initially the entire scene is "novel" and the output of the filter is the entire scene. Eventually, the scene is no longer so novel: It fades from the output as the system adapts. Now a bird enters the scenesomething that wasn't there before. The output of the filter shows only the flying bird. After the bird lands, the system adapts to the change in the scene, so once again there is no output.
Development of IV–VI compounds for gradient index materials (GRIN) optics
Authors: Tremblay C. , Gelfandbein V. , Van Neste A.
Published: February 2023

Gradient index materials (GRIN) are defined as those in which the refractive index (n) varies spatially. Lenses possessing both radial and axial gradients of n, because of their unique ability to correct Petzval field curvature and chromatic aberration, are not equivalent to anything in current lens design. We have developed bulk GRIN materials for IR applications based on GexSi1−x and GexSi1−xTe(IV–VI) semiconducting compounds. The GexSi1−x compound has an excellent transparency range, from 1.9 m to over 18 m, and shows no profound absorption peaks. By controlling the solidification parameters, both axial and radial profiles can be varied from linear to parabolic, a considerable departure from the simple law of normal freezing. The maximum gradients of the refractive index (n) in GexSi1−x for radial and axial profiles are equal to 0.2 cm−1 and 0.1 cm−1, respectively. Although having an inferior transparency characteristic, the GexSi1−xTe compound shows higher n: 0.3 cm−1 and 0.2 cm−1, respectively. Electrical resistivity () along with microhardness (H) measurements have also been performed. Both radial and axial variations of and H are in excellent agreement with optical tests. A model for the evaluation of the refractive index, resistivity, and microhardness is presented. Expressions interrelating n, and H are derived by using the energy-gap concept as an unified parameter. By measuring either resistivity or micro-hardness profiles, the refractive index gradient can be estimated. Assessments of the applicability and the limitations of the theory are given.