bluuebunny/crossref_metadata_2025 huggingface dataset:
Cooling and trapping atoms using diode lasers
Authors: Wieman Carl E.
Published: February 2023

There has been considerable activity recently on cooling and trapping atoms using laser light. This work raises expectations that laser manipulation of atoms will be an important new tool for atomic physics. However, up to now, almost all the work has been on sodium atoms using light from dye lasers. The expense and complication of a narrowband dye laser system is a considerable limitation on the possible uses of this tool. In response to this we have been exploring the use of inexpensive diode lasers for the manipulation of atoms. We have found that diode lasers work very well for this purpose and even have some advantages over dye lasers in addition to cost and ease of use. We previously reported using light from diode lasers to stop a beam of atomic cesium. Here we discuss our more recent work using diode lasers to produce extremely cold cesium vapor via optical molasses cooling and the demonstration of a new type of optical trap. This is a purely optical spontaneous force trap which uses spatially inhomogeneous optical pumping to circumvent the optical Earnshaw theorem.
Characterization of sodium optical molasses
Authors: Lett Paul D. , Gould P. L. , Phillips W. D.
Published: February 2023

The general features of optical molasses,1 continuously loaded with slow sodium atoms, are described. Three orthogonal pairs of counterpropagating laser beams, tuned slightly below resonance, capture and viscously confine the slow atoms which are produced continuously by a Zeeman tuned laser-cooled atomic beam.2 The continuous loading of this molasses region is further enhanced by using optical depumping techniques (optically pumping the atoms out of the cooling cycle with another laser) to extract more slow atoms from the beam than are otherwise available. Results from simple analytic theories and Monte Carlo simulations of the molasses are compared to the experimental findings. In particular, we look at the molasses lifetime as a function of beam imbalance and laser frequency. Although some features of the molasses can be explained (in particular at low intensity) many discrepancies are noted. One most obvious of these is the relative insensitivity of the lifetime to intensity imbalance, the discrepancy being at least an order of magnitude in added rate.
Continuous stopping and trapping of neutral atoms
Authors: Bagnato V. S. , Lafyatis G. P. , Martin Alexander G. , Helmerson K. , Pritchard D. E.
Published: February 2023

We have continuously stopped thermal sodium atoms with laser light and loaded them into a 0.1-K deep superconducting magnetic trap. The trap is formed by a local minimum of the magnetic field produced by two superconducting coils and a radially confining octupole field. The atoms are slowed and stopped in two stages: The atoms are first slowed to ~200 m/s using a counterpropagating resonant laser beam and tapered magnetic field to compensate for the changing Doppler shift as the atoms are slowed.1 A second laser beam and tapered magnetic field, actually located within the trap, are used to stop the atoms in the trap. This continuous loading process has allowed us to accumulate up to 1 × 109 trapped atoms, and trapping times of several minutes have been achieved. Our trap has the feature of having a uniform magnetic field at its bottom, opening up the possibility of precision spectroscopy of the trapped atoms. The fluorescence from the trapped atoms has been studied, and they have been cooled to ~1 mK using 1-D optical molasses.
High-order cyclo-Raman excitation of a single electron by a laser
Authors: Ding Y. J. , Kaplan A. E.
Published: February 2023

It was shown by one of the authors earlier1 that the multiphoton excitation of a free cyclotron electron can be induced by two laser beams with their frequencies ω1, and ω2 being much higher than a cyclotron frequency Ω
c
and differing either by (three-photon resonance) or 2Ω
c
(four-photon resonance). These excitations give rise to what we call cyclo-Raman scattering of laser light (of the first and second orders, respectively). Here we consider the feasibility of even higher-order cyclo-Raman excitations of an electron by laser radiation with frequencies ω1, and ω2 so that ω1, − ω2 ≈ nΩ
c
, where n is an arbitrary integer.
Deductive method of light lock moire fringes
Authors: Cao Xiang-Qun , Jin Rong , Fan Huang-Liang
Published: February 2023

We discuss two methods of obtaining the intensity of light lock fringes formed by two gratings: (1) direct calculation by which the light intensity can be obtained using an analytic formula; (2) the deductive method proposed in this paper. We give several formulas through which the deductive result can be achieved.
Applications of door peepers
Authors: Goodman Douglas S.
Published: February 2023

Ordinary security door peepers are inexpensive wide-angle viewing devices. They can be used in a variety of ways, some examples being the following: (1) Illumination can be analyzed by placing a peeper in the object plane of an imaging system. (2) Pupil aberrations are demonstrated with a door peeper placed on a light table that is viewed from various angles. (3) Zonal aberration effects in poorly corrected lenses are observed with a peeper at the image of a point source. (4) Conoscopic observation of thin crystals, e.g., a mica sheet, is performed by viewing the crystal between crossed Polaroids with diffuse rear illumination. (5) Wideangle illumination is obtained by inserting light from the narrow-field end of a peeper. (6) A poorman’s wide-angle photographic lens consists of a peeper preceding an ordinary camera.
Microwave imaging of 2-D dielectric inhomogeneity and its relation to synthetic aperture radar
Authors: Smith P. R. , Hopcraft K. I. , Burge R. E.
Published: February 2023

We present the results from an initial study of the effects of inhomogeneity and multiple scattering on the interaction of EM waves with matter and its relation to synthetic aperture radar imagery.
Scattering and Inverse scattering from bandlimited fractal slabs
Authors: Jaggard Dwight L. , Kim Y.
Published: February 2023

The fractal concept is useful in describing structures displaying dilation symmetry. Such structures are said to be self-similar. Physical structures, whether naturally occurring or man-made, are at best self-similar over a regime of interest between an appropriate inner and outer scale. Here we model such structures by a bandlimited Weierstrass function which incorporates these scales and possesses an identifiable fractional dimension denoted the fractal dimension. We call such structures bandlimited fractals. Of interest here is the scattering and inverse scattering of waves from 1-D bandlimited fractal slabs. We demonstrate exact and approximate methods for calculating the reflection from such slabs and relate the scattering data to the fractal dimension of the slab. In certain conditions, the solution of this forward problem provides a means for attacking the inverse problem. In the case of the latter, the fractal dimension is desired based on scattering data. Here we find criteria for the approximate solution of this inverse problem and demonstrate the method on bandlimited fractal slabs of varying dimension. This method is useful in the remote probing of turbulent media or in the scattering of optical waves from imperfect optical structures.
Fiber-optic gyroscope using a SWAOM: a progress report
Authors: Sun Jing , Grot Annette , Ih Charles , Mentzer Mark
Published: February 2023

When a laser beam passes through the SWAOM, two laser beams emerge: a diffracted first-order beam ψ1 and an undiffracted zeroth-order beam ψ2. The two beams are launched into the opposite ends of a rotating fiber loop. The diffracted beam ψ1 passes through the rotating fiber loop and then back into the SWAOM. When the beam ψ1 enters the SWAOM after traversing the fiber loop two beams emerge: a diffracted first-order beam ψ3, and an undiffracted zeroth-order beam ψ4. Similary the undiffracted beam ψ2 passes through the rotating fiber loop and reenters the SWAOM. The beam also becomes two beams, a diffracted beam ψ5 and an undiffracted beam ψ6. The two superimposed beams ψ3 and ψ5 can be detected by a photodetector.
Real-time polychromatic pattern recognition using a magnetooptic spatial light modulator
Authors: Javidi Bahram , Kuo C. J. , Chen Y. F. , Ludman J.
Published: February 2023

A real-time polychromatic image correlator using the magnetooptic spatial light modulator (SLM) device for pattern recognition based on both the color and shape of an input object is presented. The proposed system utilizes a multichannel spectral matched spatial filter employed in a binary coherent optical correlator. Input color images are transformed into binary color coded coherent images by a color grating with a charge-coupled device interfaced with a magnetooptic device. The color-coded binary images are then processed by a multichannel joint spectral matched spatial filter synthesized by monochromatic light.
Observation of atoms laser-cooled below the Doppler limit
Authors: Phillips William D. , Lett P. D. , Watts R. N. , Westbrook C. I. , Gould P. L. , Metcalf H. J.
Published: February 2023

By measuring the ballistic motion of sodium atoms released from optical molasses1 we determine their temperature to be as low as 43 ± 20 μK. Four different measurement techniques are used, giving temperatures ranging from 43 to 80 μK. These observations are inconsistent with the accepted theory of laser cooling,2 which sets a lower limit on the temperature of kBT = ħγ/2. This Doppler cooling limit is achieved for a detuning of Δ = – γ/2. For sodium cooled on the D2 line, γ = 2π × 10 MHz, and the Doppler cooling limit is 240 μK. We have measured the detuning dependence of the temperature and found it to be in strong disagreement with theoretical predictions. The temperature is minimized for |δ| much larger than γ/2 and is always below the cooling limit except at small detunings. These results are remarkable and unexpected; they raise important questions about the adequacy of present theories of laser cooling.
Collision dyamics of ultracold atoms
Authors: Weiner John
Published: February 2023

Recent advances in optical stopping and trapping of particles now permit the investigation of atom collision dynamics at temperatures below 1 mK. We discuss three specific examples of inelastic processes appropriate for study in this new energy domain: radiative association; collisional heating; and associative ionization. Theoretical study of radiative association and collisional heating demonstrate new quantal features apparent in the total inelastic cross section due to the small number of partial waves contributing to the nuclear motion. We present the first experimental observation of an inelastic process, associative ionization between excited sodium atoms, and report a measure of the absolute cross section ~3 orders of magnitude larger than the cross section measured in conventional conditions.
Inhibition of laser cooling in Paul traps
Authors: DeVoe Ralph G. , Hoffnagle John A. , Brewer Richard G.
Published: February 2023

Several groups have recently used laser cooling to produce ordered arrays of ions, ion crystals, in rf quadrupole ion traps (Paul traps). Laser cooling has been understood using previous theories which ignore ion micromotion and replace the oscillating rf trap potential with a static pseudopotential. We show that in recent experiments, ion micromotion can exceed one wavelength of the cooling radiation and that the resulting Doppler shifts can transform laser cooling into laser heating. Changes in trap voltage, ion position, and laser intensity can all reverse the sign of laser cooling. This, together with ideas of deterministic chaos, can lead to a reinterpretation of experiments on ion crystals. The recognition that effects previously attributed to an experimental artifact, rf heating, may actually be due to a failure of laser cooling opens the door, on the one hand, to precise theories of phase transitions and, on the other, to improved cooling techniques that can permit the creation of larger ion crystals.
High-speed high-resolution laser beam steering concept
Authors: Haskal H. M. , Adamowicz R. F. , Muller J. T. , Scott P. B.
Published: February 2023

An electronically tunable laser diffracted by an efficient grating constitutes an attractive laser beam steering concept, which combines high speed with high angular resolution. Our detailed calculations have determined the characteristics of the proposed deflector including the number of resolvable spots N
R
, the expected diffraction efficiency, and the angular speed. In the computation of N
R
we take into account the angular broadening of the diffracted beam due to the finite linewidth of the laser. The analysis indicates that using a laser with a 35-nm tuning range, a linewidth of 1 pm, and a grating with a 306-nm spacing and a 30-mm aperture, N
R
= 12,300 is realizable.
Pattern recognition using a spatial light modulator
Authors: Vaerewyck Janine M. , Caulfield H. John
Published: February 2023

The purpose of this paper is to discuss the results of a continuing study on the use of a spatial light modulator in a pattern recognition system. The SLM that is being studied was built by Lock-heed Missiles and Space Co. of Palo Alto, CA1 and is on loan to U. Alabama in Huntsville. This SLM, an optically addressed device, is being used as a spatial filter in a pattern recognition system. A computer study has been conducted to determine the best use of an SLM in such a system.
Multiwave mixing in semiconductor media
Authors: Sargent Murray , Koch Stephan W.
Published: February 2023

We consider an intrinsic semiconductor medium subject to an injection current, an arbitrarily intense electromagnetic wave, and one or two non-saturating waves. We assume that the saturating wave intensity is constant throughout the interaction region and ignore transverse variations. We further assume that the carrier–carrier scattering is sufficiently fast that the carriers are described approximately by Fermi-Dirac distributions. We find that the probe-wave propagation is described by Beer’s law or coupled-mode equations. These equations are determined by a Fourier expansion technique highly developed for two-level atoms. The absorption and coupling coefficients experience asymmetric dips generated by pump scattering off carrier-density pulsations induced by the pump–probe interference. These effects are reminiscent of coherent-dip phenomena well-known in two-level systems but differ significantly in form.
Imaging through inhomogeneous media via four-wave mixing and superresolution
Authors: Cunha Andre , Leith Emmett N.
Published: February 2023

Phase conjugation is in its basic form a double-pass technique; thus the image forms on the object side of the imaging system, which is a severe and often intolerable restriction. A single-pass technique has been described which removes this limitation, but its phase error correction capability is only approximate. We describe a method which allows great improvement in the one-way method. This method involves combining the phase conjugation method with a related method for imaging through inhomogeneities, sometimes called super-resolution by incoherent-to-coherent conversion.1 The spatial coherence of the illumination is reduced, thus leading to a partially coherent system. Also, the aperture of the imaging system is reduced, thus reducing the magnitude of the inhomogeneity. The reduction of the aperture in combination with the coherence reduction leaves the theoretical resolution unaltered. However, the residual uncompensated phase error is significantly reduced. We have previously described and demonstrated a related technique, which combines superresolution with the double-pass phase conjugation method for imaging through inhomogeneities.2 Here we demonstrate that the new configuration, using the single-pass method of phase conjugation, fits better with superresolution; therefore, imaging through inhomogeneous media can be optimized.
Effect of intensity modulation in a bistable system with delay
Authors: Yue Gao Jin , Xu Jin Gaung , Wei Sun Jian , Abraham Neal B.
Published: February 2023

We have studied the dynamic response of a hybrid bistable device with a delay in the feedback loop when the input intensity is modulated sinusoidally. As predicted theoretically, we observed several interesting effects on the system. Under the action of a small modulation in the stable region of the free-running system, we confirmed the resonance response of the output intensity when the driving frequency is in the vicinity of the eigen-frequency of the state. The nonlinear distortion of the resonant response can be seen by increasing the modulation depth. The frequency locking was carried out in conditions for which the free-running system exhibits nearly oscillatory behavior. When the system was driven at a rationally related frequency, frequency locking has been observed as one would expect in a nonlinear oscillator. When the driving frequency was held fixed and the modulated amplitude was gradually increased with the system in an unstable operating point, locking was followed by a series of bifurcations leading to very irregular and possibly chaotic oscillations.
Novel algorithms for adaptive optical components
Authors: Vandenberg D. E. , Jacques D. A.
Published: February 2023

A deformable mirror was required to input controlled aberrations to a prototype wavefront sensor. Zernike polynomials were used in conjunction with NASTRAN to optimize the locations of actuators and to construct the necessary forces to approximate each aberration requiring correction. A correction matrix was constructed using the aberrational magnitudes created by the selected actuator configuration. This approach reduces the complexity of the correction matrix from a rectangular matrix sized by the number of actuators to a square matrix sized by the number of aberrations to be corrected. By inverting the correction matrix and solving for an identity matrix, participation factors were calculated to correct each off-diagonal term representing unwanted residual aberrations. This evaluation was extended and applied to test data where any deviation from the optimum design (fabrication, manufacturing, and alignment tolerances) resulted in unwanted residual aberrations. When the off-diagonal terms were eliminated, optimal tolerance correction was accomplished.
Texture segregation by multiresolution energy or by structure gradient?
Authors: Landy Michael S. , Bergen James R.
Published: February 2023

The strength of preattentive texture segregation is strongly modulated by the density of micropatterns making up the texture. This spacing effect has been interpreted by Nothdurft [Vision Res. 25, 1957 (1985)] as evidence for the structure gradient as the primary predictor of segregation strength. If the texture involves a change in dominant orientation θ, the segregation performance should be monotonically related to Δθ/Δx. An alternative model suggests that the image be analyzed by a number of spatial filters varying in preferred orientation and spatial frequency, in which the spacing effect comes from poor SNR as a result of undersampling of the widely spaced patterns.
Reconstruction of temporally undersampled images using motion direction information
Authors: Shadlen Michael , Carney Thom , Switkes Eugene , Kersten Daniel
Published: February 2023

Several problems posed by spatial and temporally sampled moving images may be ameliorated when knowledge of visual motion direction is known. We extend prior analyses of sampled moving images through the following conjecture. For rigid motion in one direction, the image spatiotemporal Fourier transform is a surface which occupies only two diagonal quadrants of the spatiotemporal frequency plane. Although sampling introduces energy to all four quadrants, that which falls over the wrong diagonal quadrants is likely to be more detrimental to motion perception, since the energy tends to excite motion detectors signaling an incorrect direction. If the direction of motion is known at every point in an image, temporally undersampled images may be partially reconstructed by removing this incorrect energy. This conjecture serves to explain the demise of short-range motion perception at large displacements and interstimulus intervals. It also explains motion capture phenomena, cooperativity, and the coherence of sampled motion displays containing elements which are effectively undersampled.
Rotation-invariant phase-only filter
Authors: Leclerc Luc , Arsenault Henri H. , Sheng Yunlong
Published: February 2023

A circular harmonic (CH) filter invariant to changes of position and orientation is described in polar coordinates (ß,ψ) as Fm(ß) exp(jmψ), where Fm(ß) is the Hankel transform of the CH functions of the object. For phase-only CH filters, the function exp(jmψ) ensures the rotation invariance, and the phase of Fm(ß) contains the object information. A circular disk on the Fourier plane covers the CH filter in those segments of ß where |Fm(ß)| is small. This can improve the SNR and the discrimination ability. Experimental studies on the effect of input noise, background, and binarization of the phase-only CH filters are presented.
Training set selection for designing filters invariant to out-of-plane rotation
Authors: Hassebrook Larry , Kumar B.V.K. Vijaya , Hostetler Larry D.
Published: February 2023

Training set selection is an integral part of filter design and can affect filter performance. The training set selection algorithm presented here is designed specifically for single-parameter out-of-plane rotation. It is assumed that the user can vary a single angle of rotation associated with a 3-D object model from which a projected image can be obtained yielding a set of training images. In the case of only in-plane rotation with N uniformly sampled training images, the resulting N × N correlation matrix (CM) of the normalized training samples would be Toeplitz. The eigenvectors and eigenvalues of this ideal CM take on simple forms. The training set selection algorithm presented here uses this ideal CM as a basis for training set selection performance. When a training set is selected, the eigenvalues and vectors for an ideal CM can be obtained and used to generate a corresponding ideal CM. This ideal matrix is then compared (on a mean-squared error basis) with the actual CM. This resulting performance parameter is then used to reselect another training set. This process repeats until the resulting CM is a good approximation to a Toeplitz matrix.
Invariant processing of optical mapped images with a 1-D electronic correlator
Authors: Jensen A. Skov , Rasmussen E.
Published: February 2023

A novel implementation of a hybrid optical/electronic recognization system is described. The main concept of the system is an optical mapping of the Fourier transform of an input scene into logpolar coordinates. In the mapped plane both positions, rotations, and sizes are converted into shifts by logpolar mapping. By adding the intensity of the mapped image in two directions, two 1-D signals appear representing an angular and radial image representation of the original image. The 1-D signals are obtained with a cylindrical lens having destroyed the coherence of the mapped image with a rotating ground glass disk. The 1-D signal is detected with a 1024-point linear CCD array and fed to an electronic correlator where the recognition, orientation, and position measurements take place. The advantage of the electronic correlator vs an optical correlator is mainly flexibility. Optimal filter design for a collection of objects to be recognized can relatively easily be done. The performance of the presented system with respect to speed, capacity, and accuracy depends on the data for the input/output devices and on the speed of the electronic correlator. With the technology today it is estimated that one object out of 50–100 possible objects can be recognized with an angular accuracy of <5° and a relative positional accuracy of 5–10% within 0.5 s.
High brightness diode lasers using nonlinear phase conjugation
Authors: Lind R. C. , Craig R. R. , Stephens R. R. , Yen H. W. , Ng W. W. , Narayanan A. A. , Chow W. W. , Giuliano C. R.
Published: February 2023

We describe experimental results together with modeling calculations on scaling semiconductor lasers to high brightness by the use of large area diode amplifiers and optical phase conjugation. Recent results where we have demonstrated diffraction-limited single-frequency performance from a large aperture in a phase-conjugate master oscillator power amplifier configuration are presented.
Binary optical elements for coherent addition of laser diodes
Authors: Leger James R. , Holz Michael
Published: February 2023

One-and two-dimensional laser diode arrays can currently be designed to produce large amounts of optical power. In addition to high power, however, many applications require near-diffraction-limited far-field performance. This paper reviews the role of diffractive optical elements for establishing mutual coherence between lasers and producing a single-lobed far field. Grating structures have been used to superimpose an array of laser beams producing an output with single-laser divergence and increased intensity. Alternatively, diffractive spatial filtering techniques have been employed to establish mutual coherence and reduce the amount of power contained in the far-field grating lobes. Fabrication of diffractive microlens arrays are also discussed for collimating laser diode sources and correcting for optical aberrations. These lens arrays are shown to have high efficiency and very low intrinsic aberrations. Finally, free space diffraction can be used to couple lasers and establish mutual coherence across the array. High efficiency is achieved using the self-imaging properties of periodic structures.
Folded optical interconnection networks: performance analysis
Authors: Stirk Charles W. , Heinrich Mark L.
Published: February 2023

Folded optical implementations of interconnection networks are desired if, in the wire grid model of computation for VLSI, the networks require more than O(N) area or time. The strategy behind folded interconnects is both to reformat a long 1-D sequence and to transform the required 1-D operations into 2-D, so that the third spatial dimension available in free-space optical systems can be used to perform the interconnection operations.
Partially coherent imaging in the scanning microscope
Authors: Ma C. M.
Published: February 2023

Partially coherent imaging performance of the scanning microscope is considered, and a scanning microscope using tilted illumination is proposed. It is known that no matter how an object is illuminated and confined, the maximum spatial frequency with which an optical image can be formed in an optical system is fixed and can be determined only by its optical pupil function. However, better restoration of the detail to a diffraction-limited image can be achieved by means of a properly designed object stop, point detector, movement of the object, and partially coherent illumination. It has been proved that superresolution can be achieved not only in the case of low Shannon numbers but in the case of high Shannon numbers provided the object details to be resolved are nonperiodic. The imaging of a two-point object and a sinusoidal distribution object is discussed in particular. The effect of different arrangements using lenses with different pupil functions is also discussed.
Performance of new 312-mm 76° echelles with 31.6 grooves/mm
Authors: Lindblom Peter , Loewen Erwin
Published: February 2023

The multiechelle grating arrangement spectrometer aims for a wide spectral range with maximum resolution (>2 M) in a relatively compact instrument. Dispersion is based on a set of four fixed echelle gratings. The short free spectral range characteristic of high orders (>75) allows use of pressure scanning instead of tenth second of arc mechanical motions. Instrument capabilities depend on the echelle, in particular, its ruled width, on high blaze angle, large groove spacing, high efficiency, and precise match of four replicas. To improve on the first models, a new master echelle had to be ruled.
X-ray lithography in the government microelectronics program
Authors: Peckerar Martin
Published: February 2023

X-ray lithography has always been a part of the DOD
very-high-speed-integrated-circuit program. Early exploratory programs
(phase III efforts) centered around the design and construction of
point-source tools using conventional e-beam excited sources. The
goal here was to scope out the limitations and advantages of the
technology. This work has recently culminated in the delivery of the
Perkin-Elmer XSAR machine to Honeywell for pilot-line evaluation. More
recent efforts centered on using high-brightness point sources to
characterize resists and novel mask-making approaches. These programs
run parallel to DOE efforts in high-brightness synchrotron sources.
Focus is shifting to the mask-making area as the final barrier which
must be overcome before this technology is inserted on production
line.
X-ray lithography using conventional Novolak resists
Authors: Peters Darryl W. , Tomes David N.
Published: February 2023

A new laser-based soft x-ray lithographic technology is described that was developed to utilize conventional resists. It is well recognized that x rays offer better resolution, larger depth of field, larger process latitude, better critical dimension control, and immunity to typical clean room defects when compared to existing or emerging ultraviolet lithographic technologies. Previous x-ray technologies utilized low-yield electron impact tubes that produced hard x rays which were inefficiently absorbed in Novolak resists. This required special hypersensitive resist materials to achieve modest wafer throughputs at the expense of process latitude and process tolerance. Soft x rays (i.e., photon energies <1 keV) are efficiently absorbed in Novolak resist producing exposure sensitivities comparable with that achievable with ultraviolet photons (i.e., E
0
of 50–100 mJ/cm2). The high brightness Hampshire laser-based source is capable of producing 10–20 mW/cm2 yielding throughputs of twenty to forty wafers per hour depending on the resist's sensitivity. The source produces x rays from 0.8 to 2.0 nm with ~75% of the incident energy at wavelengths of 1.2-1.6 nm.
Soft x-ray imaging of nanostructure patterns
Authors: Attwood D. , Vladimirsky Y. , Kern D. , Meyer-Ilse W. , Guttmann P. , Greinke B. , Chang T.H.P.
Published: February 2023

Fresnel zone plate lenses with outer zone widths of 40 nm have been used to image various nanostructure patterns with a spatial resolution approaching 50 nm (0.05 µm). Radiation at 4.5-nm wavelength was utilized at the BESSY synchrotron facility in Berlin using the Gottingen x-ray microscope.12 The test patterns include periodic line structures, circular structures, and various patterns associated with a 0.1-µm test circuit. Feature sizes of the test patterns are well resolved at 60 nm.
Fiber lasers and amplifiers
Authors: Miniscalco William J.
Published: February 2023

Recently there has been a renewal of interest in the use of fibers doped with optically active ions, principally rare earths, as active devices in optical fiber communications and sensor systems. This increase in activity has been driven by improved methods for incorporating dopants into telecommunications-grade fiber, the availability of laser pumps, and the requirements of advanced fiber-optic systems. Single-mode silica fiber lasers, optical amplifiers, and superluminescent devices exhibiting exceptional performance have been demonstrated at many laboratories. Results have included laser thresholds of <100 µV, slope efficiencies of >50%, and tuning ranges exceeding 70 nm. Q-switched and single-frequency operation have been achieved, the latter with linewidths of ≤1 MHz. Both Nd3+ and Er3+ have been pumped by 0.8-µm diode lasers; the all-fiber mirrors and ring lasers have been demonstrated. Optical amplifiers have produced gains of >30 dB at 1.55 µm and appear to have good noise properties, while superluminescent single-mode fibers have generated powers of > 10 mW at 1.06 µm. Major issues limiting performance include excited-state absorption, which Inhibits gain for Nd3+ at 1.3 µm and reduces the pumping efficiency for Er3+ as well as the peak gain vs optical bandwidth trade-offs.
Heterodyne interferometric polarimeter for Stokes parameter measurements
Authors: Calvani Riccardo , Caponi R. , Cisternino F.
Published: February 2023

The polarimetrie heterodyne interferometer (PHI) is an interesting tool for real-time detection of a rapidly changing state of polarization (SOP) of a coherent optical radiation.1 This versatile instrument, which has been demonstrated for fiber characterization, provides amplitude ratio and relative phase of the two optical field components Ex, Ey. A more complete SOP determination (applicable also to partially polarized light) requires the use of Stokes parameters.2 In the present work, this purpose has been achieved by modifying the output electrical scheme of the PHI: the two detected heterodyne signals, proportional to Ex Ey, are split and mixed together with and without 90° electrical delay to provide s2, s3 Stokes parameters (s1 could be derived also from the two rf outputs, while s0 requires an independent radiometric measurement). s2, s3 outputs have been tested using a Pockels cell at low frequency and properly oriented to obtain only an SOP phase modulation (with nearly 180° depth). The s2, s3 output curve, visualized through an x-y oscilloscope, turned out to be a circular arc as expected.
Parallel processor for optimization and estimation problems: architecture
Authors: Shoemaker R. L. , Landesman A. , Seacat R. H. , Barrett H. H.
Published: February 2023

In image reconstruction problems in nuclear medicine, as well as in optimization and estimation problems in other areas of optics, one wants to find a best estimate of some quantity. Such problems can often be reduced to finding a global minimum in some multidimensional energy surface. Simulated annealing is very effective for these problems, but it is also very computationally intensive.
Self-pumped phase conjugation in sodium vapor
Authors: Gaeta C. J. , Lam Juan F. , Lind R. C.
Published: February 2023

We have used a two-wave mixing gain process in sodium vapor to construct a self-pumped phase conjugator. This was done by forming a resonator around a quartz sodium cell equipped with Brewster angle windows. A pump beam is then directed into the sodium cell at a small angle to the longitudinal axis of the resonator. At sufficiently high cw pump intensities, the ac-Stark effect pro- vides sufficient gain to achieve oscillation. Although this gain is unidirectional it occurs on the wings of the sodium resonance so that the backward traveling optical field in the resonator does not experience loss due to sodium absorption. The counterpropagating optical fields in the resonator interact with the pump in an internal four- wave mixing process to produce a fourth optical field (phase conjugate to the pump field). Our experiment was conducted at the sodium D2 resonance. The pump laser was a 699 autoscan single frequency ring dye laser providing pump intensities up to several hundred watts per square centimeter.
Coherent beam couplings and self-oscillations in BaTiO3
Authors: Venkateswarlu Putcha , Sekhar P. Chandra , George M. C. , Dokhanian M. , Miahnahri A.
Published: February 2023

A poled BaTiO3 crystal (8×8×6 mm3) is pumped by mutually coherent beams A1 and A2 in horizontal polarization from a multilongitudinal mode Ar+ laser (4765 Å). The angle between A1 and A2 is 40°, while A2 makes ~25° with the c axis in the horizontal. The self-pumped phase-conjugate beams A1 and A2 are steady under individual pumping when the beams enter the crystal through the center of the face.1 If the point of entry is ~1.5 mm from the edge nearest to A2, A2 shows systematic oscillations whose frequency increases with laser wavelength and power, while A1 continues to be steady. If both beams pump simultaneously the detectors D1 and D2 of A1 and A2 show about sixteenfold increase in intensities with coherent but irregular pulsations. This is because of the mutual fanning of A1, and A2, which leads to their Bragg diffraction1,2 into the reverse directions of each other to D2 and D1, respectively.
Recovering view and world geometry from stereo disparities
Authors: Wildes Richard P.
Published: February 2023

Given a pair of matched stereo images how is it possible to recover the stereo viewing parameters as well as the 3-D scene geometry? This problem has received considerable attention in both the vision and photogrammetric literature. Typically, solutions have been iterative in nature and/or numerically unstable. Here a new analysis is presented which leads to numerically stable closed-form solutions. The analysis begins by considering stereo disparity and its gradient. It is shown that the unknown viewing parameters and 3-D world geometry can be related in terms of horizontal and orientational disparities. (Orientational disparities are defined as the difference in imaged orientation of world surface detail.) This first part of the analysis is similar in spirit to Koenderink and van Doorn.1 The variables are further related by invoking a simple constraint: For stereo viewing the two eyes should be focused on the same world point. With this analysis in place, it is shown that the unknown quantities (viewing parameters and world geometry) can be recovered in terms of measurable quantities (horizontal and orientational disparities) via a quasilinear system of equations.
Linear phase coefficient composite filters
Authors: Hassebrook Harry , Vijaya Kumar V. B. K. , Hostetler Larry D.
Published: February 2023

A new approach to composite filter design is presented in which the filter is the weighted sum of training samples with the complex weights being of unit magnitude and linear phase. The LPCC filters are based on the fact that when the N training images are uniformly sampled in in-plane rotation, the resulting N×N correlation matrix (CM) is Toeplitz. The training set for out-of-plane rotation is chosen so that its CM most closely resembles the Ideal CM for in-plane rotation. The eigenvectors of the ideal CM are used to obtain the coefficients needed to generate the LPCC filters. The elements of these eigenvectors are complex exponentials which have unit magnitude and linear phase. The resulting magnitude response from such filters is constant (equal to the associated eigenvalue). The outputs of these filters are combined into a filter bank response based on the Bayes minimum probability of error criterion.
Rotation-invariant optical pattern recognition with increased information content
Authors: Putnam Robert S.
Published: February 2023

Past work in optical pattern recognition of rotated targets emphasized smeared Fourier plane filters or synthetic discriminant functions. These are reduced information content filters. Our aggregate phase-only filter detects multiple targets whose Fourier transforms have minimal overlap, which utilizes unoccupied areas of the Fourier plane and which reduces smearing. This retains effective target detection for all targets. Using multiple targets which are rotated versions of the same image, we demonstrate that an aggregate filter formed from widely rotated targets performs better than one formed from slightly rotated versions. The strong overlap of the Fourier transforms of the similar targets leads to choosing compromise values for the phase in the Fourier plane filter. The Fourier transforms of the dissimilar targets had less overlap and permitted choosing the phase of each pixel in the detection filter to match only one of the targets. The correlation peak amplitude has also been predicted as a function of overlap in the Fourier plane for the aggregate filter with two, three, four, and five simultaneous targets. Rotation invariance is obtained by using several aggregate filters in parallel, each of which detects several widely separated angular positions of the target.
Optimization of ternary correlation filters for distortion invariance
Authors: Flannery David , Milkovich Mary , Loomis John , Lindell Scott
Published: February 2023

Ternary phase-amplitude filters (TPAFs) are a discrete-valued correlation filters which may be viewed as an extension of binary phase-only filters (BPOFs) by adding a zero-modulation state. Modulation values of −1, 0, and 1 are encoded. The TPAF also has the potential for relatively simple real-time implementation but with much improved performance enabled by the additional modulation state, which allows blocking of some spatial frequencies. This paper reports simulation results demonstrating the design of TPAFs incorporating both in-class distortion invariance and out-of-class discrimination and compares the results with those obtained using other filter formulations.
Detection of rotational and scale varying objects with a programmable joint transform correlator
Authors: Yu Francis T. S. , Tam Eddy , Li X. , Jutamulia S. , Gregory Don A.
Published: February 2023

Pattern recognition requires the identification of an object with unknown orientation and variable scale. To solve this problem, multireference images can be used. However, there is a limit space-bandwidth product available in the optical system. A large number of references would essentially saturate the image space which would degrade the accuracy and the reliability of detection. To implement multiple references in the same plane, the information content of each reference image must be reduced. This reduction is achieved by using only the edge information in the reference image. In general, using an edge-enhanced image provides higher accuracy of detection, thus reducing the ambiguity of the spatial content. We note that the joint transform correlator has advantages such as simplicity in reference generation and lower resolution requirements, which are very suitable for electrically addressed low-resolution spatial light modulators such as LCTVs.
Solitons in stimulated two-photon scattering
Authors: Druhl Kai
Published: February 2023

Stimulated two-photon processes (such as Raman and Brillouin scattering) admit solitons in which the transfer of optical energy from the pump is reversed. In the presence of coherence decay, solitonlike waves can be created by phase shifts in amplifier configurations. Temporal narrowing and, in the presence of detuning, pulse decay occur. We review the basic theory of these phenomena, experiments, and possible uses.
Reduction of noise effects In photoacoustic absorption measurement of liquid samples including suspended matter
Authors: Hirono Junza , Nishimoto A. , Saito T. , Kakui Y. , Nanjo M.
Published: February 2023

The photoacoustic technique is used to measure absorption spectra for various samples and is confirmed theoretically and experimentally to be suitable for condensed opaque samples by a gas-microphone method. For liquid samples including suspended matter, however, scattered optical radiation impinges on the surface of the transducer for detecting a photoacoustic signal and generates spurious noise. Consequently, photoacoustic measurement has not been applied directly to the samples including suspended matter.
Light-induced erasure of χ(2) gratings in optical fibers
Authors: Ouellette Francois , Hill Kenneth O. , Johnson Derwyn C.
Published: February 2023

It has recently been shown that a phase-matched χ(2) grating can be written in an optical fiber by irradiating it simultaneously with light at the fundamental and harmonic wavelengths for a period of time.1 We have found that this χ(2) grating can be erased optically by irradiating the fiber with light of suitable wavelength and intensity. Gratings written with light at 1.06 μm and 532 nm in a single-mode germanium-doped fiber (with no phosphorus) were erased when only the mode-locked Q-switched light at 532 nm was launched into the fiber. Irradiation with intense light from a cw argon laser also accomplished the erasure. The decay of the conversion efficiency as a function of irradiation time was not exponential but could be fitted to a model where the amplitude of the grating A decays proportionally to A2. The decay constant was found to be proportional to I
n
, where n = 4.4 + 1.2 and I is the erasing intensity.
Self-phase modulation, self-focusing, and diffraction in homogeneous media and graded-index optical fibers
Authors: Manassah Jamal T. , Baldeck P. L. , Alfano R. R.
Published: February 2023

The simultaneous effects of self-phase modulation, self-focusing, and diffraction on the propagation of ultrafast pulses in homogeneous and graded-index media are described. Approximate analytical solutions for the Gaussian diameter, temporal pulse shape, and pulse phase are derived. Numerical calculations of the supercontinuum generated by picosecond and femtosecond pulses are performed. The pulse phase, shape, and frequency modulation are shown to differ strongly from the plane-wave theory of self-phase modulation. At low intensity, the phase of a diffracting beam is given by p(z) = w0t−kz + n(z), where n(z) = arotan (z/z0) is a corrective longitudinal phase term due to diffraction. Our work shows that for a finite beam size or graded-index media, both the nonlinearity and diffraction contribute to this phase. We show that the sign of the time-dependent phase changes as a function of pulse energy. In a certain energy range red-shifted and blue-shifted frequencies are generated at the trailing edges of the pulse, respectively. Therefore, the pulse compression of ultrafast pulses may be obtained simultaneously with spectral broadening in the nonlinear medium without the use of grating pairs or prisms.
Mechanism for efficient second harmonic generation in Ge- and P-doped optical fibers
Authors: Lawandy N. M.
Published: February 2023

The discovery by Osterberg and Margulis of efficient (>5%) conversion of 1.06-μm light to the second harmonic (0.532 μm) in a P2O5:GeO2:SiO2 glass fiber has resulted in an interesting yet unexplained physical effect. We believe that the defect responsible for this effect is a clathrate structure or interstitial trapping of a GeO molecule. The maximum doping of ~10% mol of GeO2 into the SiO2 network may result in extra GeO molecules, which are interstitially trapped during preform fabrication. The GeO molecule has an inter-nuclear separation of 1.786 and 1.650 Å in its ground (A1∑+)and excited (X1∑+) states, respectively. GeO is rotationally frozen in its A1∑+ state, while multiphoton optical excitation of the X1∑+ state (~2600 Å) by three photons (2ω + ω + ω) at 1.06 μm allows the GeO guest molecule to reorient itself. The threshold for preparation is believed to be due to the onset of a parametric instability in vibrational Raman scattering (~1 GW/ cm2). The symmetry of the diffusional reorientation process of the GeO molecule is broken by its dependence on the 2ω field strength, which is in turn coupled to the local ensemble orientations of the GeO molecules. This process results in an asymmetric angular random walk, which preferentially self-organizes the fiber to maximize its doubling efficiency. Phosphorous oxygen hole centers are two-photon pumped at 1.06 μm and emit photons between 2 and 2.5 eV helping to initiate the reorientation.
Modal transients In pulsed laser diode arrays
Authors: Lippincott Wendy L. , Collins W. C. , Clement A. E.
Published: February 2023

The pulse response of the individual modes of laser diode arrays is examined. We have recently observed considerable power sharing over an extended period of time among the modes of these lasers. The amplitudes of the modes can increase or decrease as much as 35 % for a period of 60 ns. This is important when considering these lasers for communication devices where the receiver samples are only part of a dispersed optical beam.