bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations on Ring Formation in Magneto-Optically Trapped Sodium Atoms
Authors: Bagnato V.S. , Marcassa L.G. , Oriá M. , Surdutovich G.I. , Zilio S.C.
Published: February 2023

In this report we present the experimental observation of rings of sodium atoms in a cold vapor cell and a theoretical model based in the existence of vortex forces leading to stable circular orbits. The apparatus for this experiment consists of a Zeeman-shift spontaneous-force trap(1), similar to the one used for Cs atoms(2). The magnetic field is produced by a pair of anti-Helmholtz coils and the three circularly polarized retro-reflected laser beams are tuned to the 3S1/2 (F=2) → 3P3/2 (F=3) transition of sodium. All laser beams carry a 1712 Mz sideband frequency working as a repumper for atoms in the 3S1/2 (F=1) ground state. When all beams are well aligned with respect to the retro-reflection and magnetic field and are detuned 10 MHz below resonance, we observe a bright ball with 1 to 2 mm at the trap center. If one of the beams is misaligned by a small rotation of the retro-reflector, the initially spheric ball deforms to a dwell shape. When a second beam is also misaligned, the formation of a ring is observed. The ring increases its radius and keeps the same width as the laser is scanned to larger values of red detunings, as shown in Fig. 1. For detunings larger than Δ = 25 MHz the ring disappears. By adding a small misalignment to the third orthogonal beam we observed a change of the plane where the ring is formed.
Experimental characterization of the intensity and phase of asymmetric 60fs pulses from a CPM dye laser
Authors: Beck M. , Walmsley I.A.
Published: February 2023

The 60fs-duration pulses generated by a colliding-pulse modelocked (CPM) dye laser have been fully characterized, for the first time, by measurements of their electric field using the frequency-domain phase retrieval method.1 The pulses are close to hyperbolic secant in amplitude, but with slightly more energy in the trailing edge, and are downchirped. This measurement provides direct evidence of the pulse asymmetry inferred by Finch et al.2
In-situ measurement of complete intracavity dispersion in an operating Ti:Sapphire femtosecond laser
Authors: Knox W.H.
Published: February 2023

The physics of passively modelocked Ti:Sapphire femtosecond lasers is a topic of current interest. In the broadband case (short pulses) the net intracavity dispersion is an important limit in determining the pulse width and tuning behavior. We report a remarkably simple and powerful technique for the characterization of dispersion in broadband tunable passive modelocked lasers. A CW-pumped passive modelocked laser chooses its cavity roundtrip time independent of the pump laser cavity length, of course. If we simply note that the cavity roundtrip time at any particular frequency is exactly the total group delay of a quasi-monochromatic wave packet at that frequency, then clearly by accurately measuring the cavity repetition rate as a function of frequency while tuning the laser, we obtain the group delay as a function of frequency directly. The changes are small: a 100 fs group delay change in a 10 ns period corresponds to a frequency shift of only 1 kHz, which is easily measured with a high precision frequency counter. Using this simple technique, we demonstrate the effect of translating a Brewster prism, and show the magnitude of the cumulative cubic phase in an actual operating laser. The signals contain contributions from mirrors, materials, air and refraction. This appears to be a powerful and simple technique which should provide useful information for understanding of the new class of broadband tunable femtosecond lasers.
Laser Surface Modification of a Low Carbon Steel with Tungsten Carbide and Carbon
Authors: Shen J. , Grünenwald B. , Dausinger F.
Published: February 2023

For many industrial applications it is sufficient to have a small area of wear resistant surface. For this reason, cheap low carbon steel is chosen for the partial laser surface alloying. Laser alloying experiments of low carbon steel (16MnCrS5) were carried out by powder injection (WC/Co 88/12) and with graphite precoating for comparison. In addition, melt injection of tungsten carbide was used to produce a composite layer with hard tungsten carbide particles embedded in tough metal matrix. Detailed material investigations (metallographical, electromicroscopical and EDX-analyses) were undertaken on the samples obtained with these methods.

The experimental results indicate that for the samples alloyed with carbon, the hardness increases due to martensitic transformation. In the case of alloying with tungsten carbide powder, the hardening mechanism can be subdivided into two regimes: for the low tungsten concentration in the alloyed layers the hardness is increasing due to the martensitic transformation, while for the high tungsten concentration the increase in hardness is mainly resulted from the higher carbide amount in the alloyed layers. Abrasive wear tests on layers alloyed with tungsten carbide indicate that the wear resistance of martensite hardened layers is comparable with that of conventional hardened 100Cr6 steel and the wear resistance of tungsten carbide composite layers is comparable with taht of sintered WC/Co hard metals. By these results a microstructure can be produced as required to suit different wearing situations.
Using television to present the technology
Authors: Collins Marty
Published: February 2023

There is no more effective medium with which to communicate, train, and present. The measure of a program’s success, however, is more a function of thoughtful and professional planning rather than an exercise in slick effects and visual gymnastics. Appropriate use of the medium includes: 1) process orientation, 2) adequate preparation, and 3) qualified vendor support.
Spatio-temporal tuning of temporal frequency mechanisms
Authors: Billock Vincent A. , Harding Thomas H.
Published: February 2023

Billock and Harding (ARVO, 1991) derived three temporal frequency mechanisms responsible for the independent detection of temporal modulated 4 c/deg gratings. Here we extend this approach to a wide range of spatial frequencies. We measured binocular spatio–temporal contrast sensitivity in thirty young (18–35 yr) observers. The stimuli were presented at 100 cd/m2 and were embedded in an extended surround of the same luminance and chromaticity. Spatial frequency ranged from 0.5 to 22.6 c/deg in steps of an octave. Temporal frequency ranged from 0.25 to 32 Hz in steps of 0.5 octave. For each spatial frequency, a temporal frequency contrast sensitivity correlation matrix was computed. These matrices were factor analyzed and solutions for 1–4 factors were varimax-rotated to obtain easily interpretable structures. Our criteria for the discernment of mechanisms were the variance accounted for by each factor and the meaningfulness of the derived tuning. Based on these criteria we found evidence for three broadband temporal frequency mechanisms: (1) a high temporal frequency mechanism with a maximum near 8 Hz and a spatial frequency range of 0.5 to 5.7 c/deg; (2) an intermediate temporal frequency mechanism with a peak near 2 Hz and a spatial frequency range of 0.5 to 4 c/deg; (3) a low temporal frequency mechanism, with a peak between 0 and 0.5 Hz at spatial frequencies > 2 c/deg.
Local and global integration in spatial localization
Authors: Wang Hong , Levi Dennis M.
Published: February 2023

E. Herring (1899) proposed that spatial integration is important for precise spatial localization. To investigate the role of spatial integration in foveal spatial hyperacuity, we measured three line bisection threshold. The center horizontal test line was also continuous (100% sampled), while the outer reference lines were randomly undersampled by different percentages. We varied the interline separation, line length, sample size, sampling percentage and line contrast. Our results suggest that there are two independent forms of spatial integration in spatial localization: local integration, this was revealed by varying the percentage of samples; and global integration, this is seen by varying the line length. These two forms of integration show the following properties: (1) local integration has a steeper slope (on a log-log plot of threshold vs sampling percentage) and is much more efficient than global integration; (2) integration occurs even when the effect of reduced sampling on stimulus visibility is accounted for; (3) integration saturates; the saturation point depends on interline separation. Our results suggest that there exist two independent local and global integration mechanisms and both contribute to the achievement of precise spatial localization in the human visual system.
Resonance anomalies of dielectric-layered diffraction gratings for TE and TM polarized incident waves
Authors: Wang S. S. , Magnusson R.
Published: February 2023

Grating anomalies are natural phenomena associated with diffraction gratings. Three categories are defined to distinguish the different types of anomaly: Rayleigh wavelength, resonance, and surface plasmon. In this paper, the guided-mode resonance characteristics of dielectric waveguide diffraction gratings are studied by the rigorous coupled-wave theory. For weakly modulated gratings, it is shown that elementary waveguide theory can be used to locate the resonances and define associated parametric ranges. It is also shown that the transverse field equation describing the field distribution across waveguide structures can be used to express the ratio of the complex amplitudes of the spectral orders on the grating boundaries. It is found that unslanted dielectric diffraction gratings at the first Bragg condition or normal incidence exhibit almost complete energy exchange between the forward and backward propagating zeroth orders. For waveguide gratings with identical parameters, the resonance characteristics are compared for TE and TM polarized input light. The resonances generally occur at different locations and the linewidths of the propagating zeroth orders are also different.
Design of a periodic grating for linear measurement of a laser beam diameter
Authors: Awwal A. A. S. , Power G. , Mitchell C. , Cakmakci S. , Gogineni S. , Hilb M. , McDonough M.
Published: February 2023

The beam radius is measured exploiting the relationship between the beam diameter and power transmitted through the grating. Gratings of various functional characteristics, such as rectangular, periodic,1 and aperiodic2 grating, have been used for laser beam diameter measurement. However, the calibration curve relating the beam radius to the minimum to maximum power ratio is nonlinear in nature. In this work, we propose to design a novel periodic grating so that the relationship is linear. Numerical least-squares technique coupled with generalized Fourier series is applied to fit the characteristics curve to a straight line. Depending on the choice of Fourier coefficients several designs are shown. Gratings of such characteristics can be fabricated by the contact screen method. We believe this to be the first known grating designed with this approach.
Beam splitter cube for white light interferometry
Authors: Farr Keith B. , George Nicholas
Published: February 2023

We describe a technique for constructing beam splitter cubes in which we monitor the optical path difference with a wavelength tunable laser. A white light interferometer should have path lengths equal to within λ/4. A larger path difference results in reduced fringe visibility and loss of signal-to-noise ratio. The beam splitter must be manufactured so that the two paths through glass are equal. We discuss the tolerance placed on the cube. One can assemble the cube from two right angle prisms in optical contact and in near perfect alignment. Alternatively, we adjust the OPD to zero by sliding the prisms into proper alignment on a layer of uncured cement. Using a dye laser, we have readily achieved acceptable path differences. This method of measuring the OPD with a tunable laser is shown to be useful for alignment of interferometers and measurement of aberrations in lens systems. A laser diode can be tuned by changing its operating current or temperature. We report results of optical path difference measurements using a laser diode.
Image plane movement stability in Fabry-Perot interferometry
Authors: Goad Joseph H. , Romanczyk Kazmere C. , Engle Charles D.
Published: February 2023

Measurements and calculations have been completed for a Fabry-Perot interferometer that establishes the amount of image plane movement that can be tolerated for a given wavelength error requirement. The fringe system from a Fabry-Perot interferometer is circular with diameters of quadratic spacing. The fringe diameters are detected using a linear CCD photodiode array that is positioned through the diameters of the circular fringe pattern. In this paper, the wavelength errors are investigated that are induced by a detector array not remaining precisely on the interference fringe diameters. To obtain a required wavelength accuracy, these results are applied to the optomechanical mounting requirements of the Fabry-Perot interferometer, output imaging lens, and photodiode array.
Agile beam director for laser radar
Authors: Neff Brian W. , Dunn Murray
Published: February 2023

The ROBS program (Rapid Optical Beam Steering) was initiated to develop new techniques for rapid random-access beam steering of large aperture transceivers over wide fields-of-regard to enhance the capabilities of tactical and strategic laser radars. A new type of preobjective optical scanner provides diffraction-limited imaging for a 0.5-m aperture over their instantaneous field of view (IFOV) with rapid random access over a 30° field of regard (FOR). The designs are compatible with IR-visible wavelengths, usable as a transmitter and/or receiver, scalable to larger apertures (up to 2 m) and space qualifiable. The optical components are fabricated using conventional techniques.
Picosecond photoelectron spectroscopy as a probe of vibrational dynamics
Authors: Knee J. L. , Lakshminarayan C. , Smith J. M.
Published: February 2023

The form of the ion spectrum in multiphoton ionization photoelectron spectroscopy (PES) depends on the vibrational character of the resonant intermediate state through which ionization takes place. This dependence is due to the intermediate state to ion transition Franck-Condon factors and thus PES is sensitive to the vibrational character of the intermediate state. In picosecond laser pump-probes PES the probe pulse interrogates the time evolution of the intermediate vibrational states by analyzing the form of the PES as a function of pump-probe delay time.1 The particular method of photoelectron analysis used is the zero electron kinetic energy (ZEKE) technique2 which affords outstanding photoelectron resolution as well as high sensitivity. Results are presented on vibrational dynamics in substituted naphthalene compounds as well as van der Waals molecules of these species. In addition some interesting results of the related ion spectroscopy of these and related species are presented.
Wavelength dependence of degenerate four-wave mixing in BSO crystal
Authors: Moghbel M. , Mago V. K. , Aggarwal M. D. , Sekhar P. Chandra , Venkateswarlu P.
Published: February 2023

Recently the wavelength dependence of the photorefractive effect has been receiving considerable attention.1 We report the wavelength dependence of degenerate four-wave mixing in a home grown and a commercial bismuth silicon oxide (BSO, Bi12SiO20) crystal. The beam from a line tunable multiaxial mode Ar+ laser in the TEM00 mode is divided into three beams, which meet in the sample in a standard configuration, with two counterpropagating pump beams of equal intensity, and one probe beam fifteen times weaker. The probe and one pump have equal path lengths to the sample. The signal is recorded with the help of a monochromator, a photomultiplier tube operated in the linear region, an amplifier and a recorder. The wavelength of the laser and the monochromator are tuned together. The intensity of all three beams are kept fixed at all wavelengths. In the wavelength region investigated (457-514 nm) the intensity of signal (arbitrary units) is zero up to ~476 nm and then rises linearly to ~150. The photorefractive grating in the commercial crystal shows single growth and decay times, whereas the home grown sample shows two growth and decay times.
Analytic frequency dispersion model of liquid water
Authors: Keil Laurens Judith E. , Oughstun Kurt E.
Published: February 2023

The experimentally observed frequency dispersion of both the real index of refraction and absorption of triply distilled liquid water over the frequency domain from ω=1×102Hz to ω=1 × 1022 Hz is described using analytic models for both the rotational and resonance polarization phenomena. In the low-frequency domain ωε[0,ω
R
], where ωR~ 1 × 1013 Hz, the real index of refraction monotonically decreases with increasing frequency, which is indicative of rotational polarization phenomena. The complex-valued dielectric permittivity over this frequency domain is found to be accurately described by the Rocard-Powles extension of the Debye model with two relaxation times. In the high frequency domain ω > ω
R
, anomalous dispersion in the real index of refraction is observed, which is indicative of resonance polarization phenomena. The complex-valued dielectric permittivity over most of this frequency domain is found to be adequately described by a multiple resonance Lorentz-like model with a minimum of four distinct resonance frequencies. The complex-valued dielectric permittivity ε(ω) = ε
R
(ω) + ε
L
(ω), where ε
R
(ω) is described by the multiple relaxation time Rocard-Powles model, and where ε
L
(ω) is described by a multiple resonance Lorentz-like model, is fitted in a least-squares sense to the real index of refraction data. The resultant analytic description of the frequency dispersion of water is essential for the asymptotic description of ultrashort pulse propagation in that medium.
Nondiffracting approximated Bessel beam (J1)
Authors: Lee Hee S. , Stewart B. W. , Will D. , Fenichel H.
Published: February 2023

The nondiffracting J0 Bessel beam will be useful in spot welding, particle beam collimation and concentration, tracking, and precision alignment. The J1 beam, the first-order Bessel beam of the first kind, is also a nondiffracting beam and has a potential use in particle beam collimation or concentration. This J1 beam is simulated by using a Fourier transform lens and an annular slit, a part of which is phase retarded. A thin glass plate, covering part of the annular slit, was used for phase retardation. In essence, we simulated polygon-type slits instead of an annular slit based on the double slit interference approach. The nondiffracting hollow cylindrical beam thus obtained shows an intensity profile similar to the beam. The maximum distance of the diffraction-free propagation, as well as the intensity profile, is compared with computer simulations. There is a considerable energy loss in generating the J1 beam. We employed a holographic amplification technique to make the conversion very efficient (50%) and used holographic phase conjugation to extend the nondiffracting distance. Holographic averaging for circular symmetry was used to more closely approximate J1.
Optical parametric generation with a non-co-line matching technique
Authors: Shou-huan Zhou
Published: February 2023

To construct a compact optical parametric generator, one of two approaches can be used: cavity mirrors are brought as near as possible toward the LiNbO3 crystal or cavity reflection is performed by direct coating on both surfaces of the crystal. Both crystal and cavity mirrors rotate as a whole when tuning. Beams of pump frequency, signal frequency, and idler frequency are not in the same direction. The tuning curve of this non co-line matching technique differs essentially from the co-line matching curve. Two specific rotation angles, which relate to one certain signal frequency (and idler frequency), can be obtained. The tuning curve tends to be protruding for signal frequency and dented for idler frequency, respectively.
Generation of tunable blue light by frequency doubling of an external cavity diode laser
Authors: Wu Qun , Shen Dezhong
Published: February 2023

The performance of a diode laser can be improved by using an external cavity, which include tuning the laser wavelength, narrow spectral linewidth, and increasing the output power. These advantages are useful to generate SHG of a diode laser. By putting a KNbO3 crystal into an external cavity GaAlAs diode laser, we obtained 135 µW of blue radiation with a linewidth of 1.2 MHz and a tunable wavelength range 426.2–428.6 nm. An unpacked GaAlAs diode laser with AR coating at laser wavelength on the output cleavage plane was placed on a thermoelectric cooler so that the temperature could be stabilized. Diode laser radiation of 20 mW was focused into a KNbO3 crystal (3×3×8 mm3 with dielectric coating on the ends) by a GRIN rod lens. The light transmitted through the crystal was collimated to a grating with a focal lens. The grating was used to feed back infrared radiation and separate the blue output by its dispersion. A piezoelectric translator (PZT) attached to the grating provided fine tuning of the laser wavelength. The KNbO3 crystal was mounted in a thermoelectrically temperature-controlled enclosure. To achieve phase matched SHG in the tunable wavelength range, the temperature of the crystal was changed to track the voltage applied to the PZT by an automatically controlled setup.
Evidence for ferroelectric domain reversal in KTP waveguides
Authors: Laurell F. , Roelofs M. G. , Bindloss W. , Hsiung H. , Bierlein J. D.
Published: February 2023

Segmented KTP waveguides can efficiently generate second-harmonic (SH) light through quasiphase matching. Highly efficient interaction was attributed to domain reversal in the ion exchanged segments forming the waveguide. Four techniques are described which demonstrate that, in conditions producing high efficiency SH generators, the ion exchange does indeed produce domain reversal. The toning procedure uses a high resolution negative liquid electrostatic toner. Domain reversed segments on the c
-
-face develop positive charge on cooling and attract toner particles, while nonreversed segments repel the toner. The piezoelectric measurements utilize oscillatory force applied to KTP held between a flat plate and a needle. The piezoelectric voltage from the needle dominates the back surface. Uninverted planar waveguides produce an increased voltage, relative to an undiffused surface, while inverted waveguides yield a significantly reduced voltage. In the surface SHG experiment, 266-nm radiation is generated at the air–KTP interface. Domain inversion shifts the phase of the SHG beam by 180°C, and interference of the SHG beam with a variable-phase reference beam allows determination of domain orientation. The etchant KOH:KNO3 selectively attacks the negative face (c-) of KTP. Unexchanged regions are etched to a depth of 1–2 µm, while the domain reversed segments stand out from the surface unetched.
Optical correlator using a LCTV CGH filter and a thresholding photodetector array chip
Authors: Chao Tien-Hsin
Published: February 2023

An optical correlator using a CGH filter encoded in a liquid crystal television spatial light modulator (LCTV SLM) and a custom designed VLSI photodetector array chip is reported. A Burckhardt-type CGH filter was written in a commercially available thin film transistor-type LCTV SLM that contains 320 × 220 pixels and has a contrast ratio of ~100:1. Both gray scale and binary holographic images are reconstructed from the LCTV CGH. This CGH filter is successfully used in an optical correlator for pattern recognition experiments. To further enhance the system speed and discrimination capability, a novel CMOS 32 × 32 postprocessing photodetector array chip is designed and fabricated for the correlator peak detection. The two main novel features of this detector array are its thresholding capability and high speed. The thresholding capacity is achieved by building a comparator and logic circuits around each pixel of the detector array. Parallel detection across the entire output plane is done in each clock cycle. Digitized addresses of locations of all the correlation peaks that exceed the thresholding level are present in the output port. The speed of the detector is ~1-10 msec, depending upon the level of the thresholding current.
Postprocessing of correlation outputs to improve optical recognition system performance
Authors: Draayer Bret F. , Carhart Gary W. , Walsh Thomas R. , Giles Michael K.
Published: February 2023

Optical correlators employing magnetooptic spatial light modulators (MOSLMs) can process binary phase-only filter (BPOF) responses at kilohertz frame rates,1 making real-time recognition possible. However, aspect invariant recognition is difficult since simple BPOFs are highly sensitive to geometric distortions. Aspect invariant composite BPOFs have been developed; unfortunately, filters that achieve aspect invariance over wide distortion ranges produce reduced correlation peak values, rendering simple threshold decision rules ineffective. A statistical correlation plane filter (CPF) based on analysis of variance has been shown to improve recognition system performance.2 This paper examines a multiclass quadratic CPF based on a Bayes likelihood ratio test. The quadratic CPF allows the correlation system to be calibrated by repeatedly analyzing correlation peaks for all object–filter combinations. This off-line calibration process yields a vector of expected correlation peak values and an associated covariance matrix for each unique object with each filter in the filter bank. Once gathered, these data are used on-line to calculate the Mahalanobis distance between an observation vector of peak values obtained with an unknown object and each mean vector. Recognition based on the shortest Mahalanobis distance delivers robust performance, even when composite BPOFs are used in the optical correlator.
Optical scene preprocessing for correlator-based pattern recognition
Authors: Bergmann Sherry A. , Norin Troy R. , Freeman Mark O.
Published: February 2023

This paper presents an optical approach to the necessary preprocessing step of scene segmentation that conditions raw image information into a form useful for pattern recognition with optical correlators. Potential regions of interest (ROI) are identified and sorted from uninteresting background regions. By eliminating superfluous areas of an image, preprocessing maximizes the speed at which the correlator in the recognition system can operate. System output consists of the edge maps within these ROI. General architectures are based on correlators followed by a threshold. The ROI filter is not matched to any particular object but rather locates deviations from a homogeneous background that have the proper size (determined from available range information). These filters are based on extracting zero- and first-order moments within a window. For objects on a constant background, thresholding at zero intensity yields the object centroids. We present adaptations that allow this approach to be used on more general images where backgrounds can vary. Simulated results using FLIR (forward looking infrared) image data are shown.
Noise performance of a partially coherent sinusoid notching system
Authors: van der Gracht Joseph
Published: February 2023

A partially coherent image enhancement system capable of notching unwanted sinusoids has been previously proposed.1 This system has a fixed random checkerboard mask and a source that can be modified to notch sinusoids of various spatial frequencies. It has been suggested that the partially coherent notching system offers improved noise performance relative to a coherent notching system. In this work, the improved noise performance is explained using Fourier optics techniques. In addition, the results of a laboratory investigation demonstrate the improved noise performance.
Exact soliton solutions for femtosecond switching in a nonlinear directional coupler
Authors: Potasek M. J. , Tasgal R.
Published: February 2023

Optical information processing is being recognized for its importance over a wide range of use. The recent focus has been on all-optical switching because of its ultrafast response time. One device configuration of interest is the nonlinear directional coupler. Most descriptions of switching in these systems have involved the coupled nonlinear Schroedinger equation (NLS) that describes switching usually on a picosecond time scale.
Near threshold buildup times of individual modes in a multimode short-cavity dye laser
Authors: Hodges S. E. , Gadomski W. , Raymer M. G.
Published: February 2023

A short-cavity dye laser has been constructed to study fluctuations arising from quantum noise and mode coupling in multimode systems. Typical dye lasers (i.e., long-cavity) have been found to have cw dynamics that are dominated by coherent wave mixing effects.1 The quantum noise in these lasers also manifests itself as a variance in the buildup times of the laser light intensity. Buildup times of singlemode long-cavity lasers have been studied.2 The relative importance of quantum noise is enhanced in short cavities making the turn-on transient the dominant feature in the laser light fluctuations. We have measured the turn-on transient of individual modes from a multimode short-cavity dye laser following sudden turn-on of the pump power. The shortness of the cavity has the effect of making the decay times of the intracavity field and the molecular population similar. The observed buildup and rise times are compared with those predicted by a semiclassical multimode laser theory with stochastic noise added for several pump rates. Moreover, semiregular oscillations of the total intensity have been observed to occur in short bursts separating intervals of nearly constant cw laser output.
Spatial and temporal behavior of gain-switched Ti:Al2O3 unstable resonator lasers
Authors: Bowers Mark S. , Moody Stephen E.
Published: February 2023

Efficient high energy Ti:Al2O3 lasers are currently of interest as coherent sources for a variety of applications, such as laser atmospheric sensing. Furthermore, the output of such lasers can be converted to visible and UV wavelengths through frequency conversion processes. We report here on a novel method for modeling these lasers. The exact cavity equations of motion coupled with realistic time-dependent laser kinetics are solved numerically to obtain the 2-D radially-symmetric time-dependent electric field inside the optical cavity of an injection-seeded Ti:Al2O3 laser with an unstable resonator. The analytical model is an extension of our previous gain-loaded laser cavity model1 to predict pulsed laser performance. It is used here to model Ti:Al2O3 lasers; however, it can also be used to predict the performance of any pulsed laser, such as CO2 or Q-switched Nd:YAG. In this method, the electric field inside the cavity is expanded in terms of the diffractive transverse (Fox-Li) stationary eigenmodes of the optical cavity, with expansion coefficients that depend on time and axial distance. In this way, the electric field is guaranteed to satisfy all the boundary conditions inside the optical cavity at all times. The expansion coefficients are further expanded in a Fourier series of longitudinal modes. Even though the laser is injection seeded, we find that the inclusion of many longitudinal modes is necessary to maintain energy conversation and to appropriately model the spatial and temporal buildup of the laser pulse.
Efficient and versatile method for multiplexed imaging
Authors: Davis D. Scott
Published: February 2023

Existing approaches to multiplexed coded aperture imaging (i.e., cyclic redundant, uniformly redundant, pseudonoise, etc.) methods are based upon encoding schemes that employ 2-D masks consisting of transparent and opaque regions. These approaches have optical efficiencies that are typically ~50%, and they require a set of encoding masks containing ~N members, where N is the number of image pixels to be encoded.
Highly efficient numerical algorithm applicable to acoustooptic diffraction with arbitrary 3-D light and sound fields
Authors: Mehrl David J. , Liu Z. C.
Published: February 2023

A simple geometric interpretation of 3-D acoustooptic (AO) scattering is developed. The interpretation is unique in that it applies to arbitrary nonparaxial 3-D light and sound fields, and is developed on the basis of the well-known 2-D AO wave vector diagram. We inherently take a wave theory approach, making use of the angular plane wave spectrum concept. The method assumes weak interaction and currently applies only to isotropic AO media, as it is developed on the basis of scalar diffraction theory.
Fabrication of large aperture, high efficiency, wide bandwidth HOEs for near IR wavelengths
Authors: Aye Tin M. , Yacoubian Araz , Rodriguez Jack , Savant Gajendra
Published: February 2023

We present a simple two step method for fabrication of high efficiency, wide bandwidth holographic optical elements (HOEs). The method begins with the recording of an aberration optimized first-step hologram using highly sensitive holographic recording material of higher wavelength response, such as silver halide. The hologram is then contact copied onto a less sensitive, but high efficiency low noise recording material, such as dichromated gelatin (DCG), or Du Pont photopolymer. The efficiency and the wavelength response of the final HOEs are then adjusted and fine-tuned as required by controlled processing. Specifically, this method allows fabrication of large aperture, high efficiency HOEs in large volume for nonimaging concentrator use, such as in photovoltaic solar energy generation.
Field curvature and diffractive lenses
Authors: Sasian Jose M.
Published: February 2023

The pivotal problem1 in lens design is the correction of field curvature. In this paper the use of diffractive components for the control of the Petzval sum in monochromatic lens systems is discussed. The design, fabrication, and testing of a diffractive lens to correct field curvature are presented.
First U.S. satellite imagery of noctilucent clouds
Authors: Zeringue Kyle J. , Suggs Robert M.
Published: February 2023

Noctilucent clouds (NLC) are observed in the northern latitudes during the summer months. The clouds, thought to be composed of crystalline ice, occur between 80- and 85-km altitude where the temperature of the mesopause can dip to 120 K. These clouds can be seen by ground-based observers when the sun is 6-16° below the horizon. This viewing geometry assures that the clouds will be illuminated by the sun while the lower atmosphere is dark. Imagery collected by Delta Star is presented as well as correlated ground-based and aircraft-based observations. Narrow field of view images obtained by Delta Star resemble NLC photographs made from the ground and from aircraft. Delta Star imaged NLCs on four of the six nights the experiment was attempted, three over central Alaska and one over Finland. Corroborating observations are available for three of these four nights. Altitude measurements made from Delta Star data place the NLCs at 81-km altitude with an estimated thickness of 4 km.
Mathematical models for diode laser beams
Authors: Li Yajun
Published: February 2023

It is known that there are two mathematical models for the elliptic beams generated by semi conductor laser diodes. The first model is the simple Gaussian model,1 in which two Gaussian distributions with different widths are employed to describe the light distribution over the elliptic cross-section of the beam. The second model is known as the Lorentzian-Gaussian model2 which was established in a study of the fact that the Gaussian distribution is valid only for the light field parallel to the junction and in the perpendicular direction the field is described by the Loretzian distribution. In this paper, numerical examples are presented to clarify which one of these two models fits the measurements better, and it is shown that the simple Gaussian model has a certain advantage over the Lorentzian-Gaussian model.
Self-consistency in partially coherent ABCD systems
Authors: Kauderer Mark
Published: February 2023

Recently, a general approach to optical information processing with Gaussian Schell model light was published.1 As a first use of this theory, the problem of self-consistency or resonance in 1-D ABCD systems is considered. If the system is real, the well-known extended ABCD approach2 easily generalizes the classical fully coherent result 0≤|A + D|≤2. However, if the ABCD system contains losses, generalization is not so simple. In this case the resonator condition exhibits a more interesting structure, showing the greater complexity of partially coherent lossy systems. In addition, a simple physical decomposition of an arbitrary lossy 1-D ABCD system is also derived.
Physical origin of the gain in a model of a laser without inversion
Authors: Doss H. M. , Narducci L. M. , Scully M. O. , Keitel C. H. , Zhu S.-Y.
Published: February 2023

We consider a four-level atomic system with a degenerate or quasidegenerate ground-state doublet and two excited states. One of the upper levels is coupled to the ground doublet by a coherent field of variable strength, which we refer to as the Raman field, whose role is to create atomic coherence between the driven atomic states. The other higher lying state is coupled to the ground states when laser action develops. This model includes an incoherent pump mechanism to create some population in the top lasing state. In appropriate conditions, for the incoherent pump rate and the Raman field strength, the absorption profile of the laser transition develops gain features. We discuss the physical origin of this gain which we find to be the consequence of a population inversion between dressed atomic states. It is interesting to compare the results of this analysis with a similar study of a three-level lambda system which was previously recognized to yield lasing without inversion.1 In this case the appearance of gain can be attributed to the induced atomic coherence.
Optoradiometric modeling of passive infrared sensors
Authors: Pace Phillip E. , Kuffer F. B. , Brisbin Douglas J. , Douglas Ian , Sahara Kanji
Published: February 2023

In performing infrared (IR) target detections in an optically cluttered background, the analysis of the basic optical and radiometric relations is a first requirement for the assessment of passive IR sensors. For given target properties (temperature, emittance, and area), specified atmospheric path and sensor configuration, the SNR and clutter-to-noise ratio are estimated to determine if target acquisition can occur. The optoradiometric model described is based on an indenture of sophisticated computer modules providing ever greater radiometric detail. Such a module provides a much higher degree of accuracy for sensor performance prediction. It may be employed to determine the expected performance of a seeker in a variety of changing conditions (weather, line-of-sight, etc.) and tactical situations (nonstationary targets) that are not easily evaluated from the basic radiometric relations. The optoradiometric model combines detailed models (commercial and noncommercial) to provide sensor performance detail for higher level analyses in a variety of user defined situations. The presence of a dynamic portion to engage time-dependent scenarios enhances the ability of the model to evaluate various tactical sensor situations. This type of interdisciplinary performance model, which accurately represents the strong interaction between optics, control systems, and signal processors, allows the design of a sensor to be readily optimized for a variety of seeker configurations.
Two-photon absorption-induced thermal effects
Authors: Guha Shekhar , Kang Keith , Porter Pamela L.
Published: February 2023

In many third-order nonlinear materials, such as inorganic semiconductors or organic polymers, the imaginary part of the electronic third-order susceptibility χ3 is larger than the real part by an order of magnitude or more in certain wavelength regions. Thus, at these wavelengths, nonlinear absorption is expected to be much stronger than nonlinear refraction. However, in measurements with laser pulses that are of nanosecond or longer duration, thermal expansion of the material caused by absorption of light and subsequent heating gives rise to appreciable nonlinear refraction of the laser beam. Because both linear and two-photon absorption of the laser beam play a part in causing this nonlinear refraction effect, the nonlinearity cannot simply be characterized by a refractive-index change n2I proportional to the laser intensity I; the order of the effective susceptibility is higher than 3.
Quantitative diagnostic studies of reactive flows using tunable diode lasers
Authors: Miller J. Houston
Published: February 2023

There are many problems in combustion science in which it is critically important to have high temporal, spatial, and temporal resolution of species concentrations. These nontrivial requirements are found in situations as diverse as fundamental studies of laboratory flame structure to the emissions of products of incomplete combustion from hazardous waste incinerators. Traditional probe sampling and analysis methods are limited to spatial regions that are relatively free of particulate matter. With some exceptions, many of the optical diagnostics methods employed so far are not quantitative, and may also suffer interferences from particulates and/or polynuclear aromatic hydrocarbons. The mid-infrared region (3–16 μm) provides an advantageous slice of the electromagnetic spectrum for these measurements: nearly every molecule absorbs light here. However, because of the high density of states here, only after the advent of narrow frequency lasers has it been possible to observe isolated spectral features in reactive media.
Tunable diode laser and Fourier transform spectroscopy of low pressure premixed flames
Authors: McNesby K. L. , Fifer R. A.
Published: February 2023

Tunable diode laser and FT-IR spectroscopies are used to obtain spatially resolved species and temperature profiles in a low pressure premixed CH4/N2O flame. Vibrational temperatures are obtained from integrated absorbences measured with a diode laser. Rotational temperatures are obtained by fitting peak absorbences from fundamental and overtone bands of CO measured with a FT-IR spectrometer to a Boltzmann-type population distribution. Species profiles for CO and NO in the flame are obtained from diode laser spectra as a function of mixing ratio and burner chamber pressure. Experimentally determined species’ profiles are compared with computer-generated species’ profiles. Finally, the utility of crossed diode laser and interferometer output beams for flame diagnostics is discussed.
Design of ring array-based optical interconnect network
Authors: Li Yao , Ha Berlin , Wang Ting , Katz A. , Lu X. J. , Kanterakis E.
Published: February 2023

To overcome clock-skew and other optical interconnect implementation problems, a ring-array processor distribution and interconnect topology has been proposed. In this paper, advantages of using an optical ring interconnect for digital electronic SIMD array processing are addressed. Design issues, such as tradeoff between array size and speed/power consumption, between parallel and multistage implementation, aberration correction, implementation complexity vs network topology, etc. are presented. Optical simulations of a small size (thirty-six nodes) optical ring network with LED sources and Si PIN diode arrays are experimentally demonstrated.
Mode control of 2-D phase-locked VCSEL arrays
Authors: Warren M. E. , Hadley G. R. , Lear K. L. , Gourley P. L. , Vawter G. A. , Brennan T. M. , Hammons B. E. , Shul R. J.
Published: February 2023

Arrays of vertical cavity surface-emitting lasers (VCSELs) have recently generated considerable interest as a means of scaling up the available output power while maintaining astigmatic diffraction-limited emission. Realization of such devices will require understanding and control of the modal emission properties of phase-locked VCSEL arrays. We have performed an experimental study of the modal emission properties of 2-D VCSEL arrays and compared our results with our numerical model. The arrays were fabricated by dry etching partly through the upper mirror stack, thus creating square pixels separated by lower reflectivity channels. The near- and far-field emission patterns of regions of varying size were studied by optical pumping. The observed far-fields demonstrate out-of-phase emission into four far-field lobes, and showed decreasing lobe width and spectral width with increasing array size in agreement with our calculations. The observations indicate operation on a single-longitudinal and lateral mode for array sizes up to 10 × 10. Because of the desirability of devices that emit into a single far-field lobe, we have designed a monolithic phase shifter for the above array. This design utilizes an extra material layer on top of the upper mirror stack for alternate pixels. We expect that, with careful control of the layer thickness, the emission of each pixel will be in phase, resulting in uni-phase emission.
Laser cooling and trapping
Authors: Chu Steven
Published: February 2023

The purpose of this tutorial is to introduce the listener to the rapidly developing field of laser cooling and trapping. Doppler cooling is first discussed followed by the new mechanism of cooling based on ground-state energy level shifts in light fields with polarization gradients. Next, the basic concepts of magnetic traps, optical dipole force traps (optical tweezers), and the magnetooptic trap are considered. Selected uses of these traps and cooling techniques are given to elucidate the broad utility of these techniques.
Limitations of optical neural network interconnects
Authors: Arsenault Henri H.
Published: February 2023

Because of their speed and large number of spatial degrees of freedom, optics is a promising technology for neural networks. Many proposed optical neural net architectures use free-space interconnects to accomplish the combinations of synaptic weights that are required. One fundamental obstacle to building some such systems is the fact that two coherent optical beams may not be added or subtracted unless they are co-linear. A consequence of this is that many proposed architectures will not work, since they require the addition or subtraction of coherent beams arriving on a detector from different angles.
Rochester excellence—customer satisfaction: the quality journey continues
Authors: Brown Charles G.
Published: February 2023

This presentation addresses the environment, set of values, and system that have fostered a world-class, customer-driven organization in IBM Rochester which resulted in their winning the coveted Malcolm Baldridge award.