bluuebunny/crossref_metadata_2025 huggingface dataset:
Planar waveguide grating couplers with variable groove depth
Authors: Li Lifeng , Bates Keith A. , Erwin J. Kevin , Roncone Ronald L. , Burke James J.
Published: February 2023

The maximum efficiency for coupling a Gaussian beam into a planar optical waveguide primarily depends on two factors: the branching ratio and the leakage rate of the waveguide-grating structure. The preceding paper (MY2) describes a means of improving the branching ratio; this paper addresses the leakage rate. A beam coupled out by a grating coupler of constant groove depth has a characteristic exponential decay profile. Such a beam profile is not desirable for many applications. In the case of input coupling, beam profile mismatch between the exponentially decaying out-coupled beam and the incident Gaussian beam limits the input coupling efficiency. Since the leakage rate is influenced most strongly by the grating groove depth, a desirable beam profile can be obtained by varying the grating groove depth along the propagation direction of the guided wave. Based on simple, numerically and experimentally verifiable assumptions, a formula for the variation of grating groove depth for any required output beam profile is derived. The variable depth gratings are fabricated by using an ion beam etching technique and a computer controlled scanning slit placed in front of a photoresist grating mask under ion bombardment. The design, fabrication parameters, and the results of beam apodization are presented.
Broadband single-mode coupler
Authors: Jannson Tomasz , Wang Michel , Sun Zongjian , Strzelecki Eva
Published: February 2023

A novel compact broadband single-mode coupler is proposed. It can provide highly efficient coupling from a cw laser diode (LD) located in close proximity (and parallel) to the waveguide. It consists of a microprism and two perpendicular volume holographic gratings. Because of the specific geometry, the gratings offer opposite-sign wavelength dispersions with two independent degrees of freedom. Thus, the coupling wavelength curve can be adjusted to the waveguide modal curve with high (second-order) accuracy. As a result, the waveguide coupling is highly efficient within a broad range of LD wavelength shifts (10-100) nm). The presented prism-grating hybrid coupling system can be used in 3-D photonic processors which are based on single-mode waveguide optical horizontal and vertical communication paths. It will provide chip to chip interconnections.
Holographic structures for integrated optics
Authors: Brady D. J. , Hill K. B.
Published: February 2023

Holographic structures on dielectric waveguides are useful for conventional applications, such as distributed feedback and grating couplers, and for novel applications, such as holographic waveguiding for lateral confinement, dispersion control for nonlinear optics, spectral filtering for pulse shaping, and signal distribution for optical interconnections. We describe techniques for constructing holograms on solgel titania/silica waveguides. Holograms are constructed by photopolymerization in polyvinyl carbazole films1 placed either on top of the solgel film or between the solgel film and a glass substrate. Because the photoinitiator for hologram formation (carbon tetraiodide) is bleached out during development, gratings in the polymer film are stable and permanent. The advantages of this technology are that structures suitable for a variety of uses may be fabricated relatively easily by placing appropriate dopants in the solgel film and by recording appropriate holograms. As examples, we describe holograms for lateral mode confinement and multiple grating holograms.
Time resolved optical spectroscopy and imaging of human brain and muscle
Authors: Chance Britton
Published: February 2023

A summary was not available at time of publication.
Imaging through scattering media using a Raman amplifier
Authors: Reintjes J. , Duncan M. D. , Mahon R. , Tankersley L. L.
Published: February 2023

Using 30-psec pulses from a frequency doubled Nd:YAG laser, we have amplified and detected images with a resolution of less than 300 μm through suspensions of latex spheres and non-dairy creamer with nonscattered extinction ratios of up to e
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40. Our time-gated image amplifier can produce images under conditions in which the scattering medium is sufficiently dense that an image cannot be seen on either a streak camera or through a long-time integration on a CCD camera. The 532-nm frequency-doubled output was used both to generate a seed-Stokes pulse at 683 nm using hydrogen at 30 atm and to pump the 1-m long Raman amplifier.1 The seed-Stokes light was used to illuminate a bar chart of line spacing 0.315 mm placed immediately before a cell containing the scattering medium. The direct image, or its Fourier transform, was amplified in the Raman amplifier. The original bar chart image was then observed using an intensified camera. By using a delay to vary the time of arrival of the pump pulse at the amplifier we were able to selectively amplify the image-bearing component at the front of the pulse and so discriminate against the multiply scattered light which can extend out for many pulse durations.
Ballistic and snake signal imaging in tissue scattering walls using a picosecond multistage Kerr system
Authors: Wang L. , Ho P. P. , Alfano R. R.
Published: February 2023

One key problem to be addressed in optical detection of hidden objects inside biological tissue scattering samples is the improvement of the image signal to noise ratio. Due to the multiscattering process in highly turbid media, the strength of the ballistic signal through a thick tissue is less than 10-6 of the incident pulse. The early arrival ballistic and snake parts of the transmitted signal, which contain the least distorted image information, would be buried in the noise from the later arrival diffused light.
Imaging through tissue using femtosecond pulses and electronic holography
Authors: Leith E. , Chen Y. , Chen H. , Dilworth D. , Lopez J. , Masri R. , Rudd V. , Valdmanis J.
Published: February 2023

We describe a method for imaging of opaque objects embedded in highly scattering media, such as human tissue. The method is based on electronic holography, in which a hologram is formed on the surface of a CCD camera, the hologram is read into a computer, and the reconstruction is carried out digitally. The illumination is a train of 150-fs pulses. The scattering medium is assumed to be unstable, so that the speckle on the transmitted light changes, i.e., becomes uncorrelated, after a short time, such as ~30ms. The hologram is made during this very short exposure time, using only the first arriving portion of the light transmitted by the scattering medium, since the first arriving light is scattered least and therefore should form the best image. A key element of the technique is that many holograms are made in rapid succession, at time intervals that exceed the speckle correlation time, so that the images from successive holograms have uncorrelated speckle. We then average over many (so far up to seventy-five) holograms, thus averaging out the speckle as well as other noise, resulting in an image vastly better than the image from a single hologram. Experimental results are shown.
Results from flights of x-ray multilayer telescopes
Authors: Golub L. , Kalata K. , Nystrom G. , Spiller E. , Wilczynski J. , Barbee T.
Published: February 2023

An improved version of our rocketborne x-ray telescope operating at 63.5A was flown on 22 Feb. 1991 and again on 11 July 1991, for studies of the Solar x-ray corona. The telescope consists of a 27.5 cm diameter aspheric mirror coated with a Co-C multilayer; data are recorded on Kodak Technical Pan film and exposures varying from 1 second up to 60 seconds are obtained during the five minutes of available Solar fine pointing. Since 1989 the telescope has: 1) a new mirror and multilayer coating for improved reflectivity; 2) redesigned mirror mount for increased active area; 3) improved visible light-blocking filters for greater x-ray throughput. These modifications plus an improved procedure for focussing of the system, have increased the spatial resolution and are leading to a reevaluation of models for heating and structuring of the corona. The He 304A system uses a Mo-Si multilayer coating and an intensified CCD camera which provides live, real-time images of the Solar XUV broadcast to the ground during the flight. These are the first such images ever obtained and the system is a prototype for a wide variety of future applications.
InGaAs/InP Multiple Quantum Well Tunable Bragg Reflector Operating at 1.55 μm
Authors: Blum O. , Zucker J. E. , Chiu T. H. , Divino M. , Jones K. L. , Chu S. N. G. , Gustafson T. K.
Published: February 2023

Surface emitting lasers have wide applications in optical communications, interconnects and information processing. Active tuning and steering of such devices requires integratable, surface-normal mirrors and filters. We present here the first tunable surface-normal distributed Bragg mirror for optical communications wavelengths. The device uses enhanced electrorefraction and electroabsorption in InGaAs/InP quantum wells (QW), which comprise alternate quarter-wave layers in the mirror. The remaining layers in the 31 Bragg pair mirror consist of bulk InP. The measured zero-field transmission of the mirror is in excellent agreement with the spectrum we calculate via the optical matrix method taking into account the spectral dependence of quantum well and bulk InP absorption and refraction. When 17 V is applied to the p-i-n stack, a field of 22.5 kV/cm is dropped across a 7.34 μm intrinsic region and a differential change in transmission of 14% is obtained near 1550 nm. Our calculation shows that the spectral features can be interpreted in terms of quantum confined Stark effect of heavy and light hole excitons, and indicate that with a new contacting scheme we will attain differential transmission changes of ≈ 100 %.
Large (45meV) electron subband separation in quantum wire arrays formed by self-ordering on v-grooved substrates
Authors: Kapon E. , Walther M. , Hwang D.M. , Colas E. , Chen C. , Schiavone L.M.
Published: February 2023

Realization of uniform, dense arrays of semiconductor quantum wires (QWRs) with subband separation >kBT is important for the investigation and application of one-dimensional structures. We have demonstrated uniform arrays of GaAs/AlGaAs QWRs grown by organometallic chemical vapor deposition on V-grooved substrates showing record-large subband separation. The crescent-shaped wires are formed in situ at the comer of two intersecting {111} A planes due to diffusion of the Ga and Al species1. The smaller diffusion length of Al results in rapid recovery of the radius of curvature at the bottom of the GaAs crescents during growth of subsequent AlGaAs barriers. This recovery is characterized quantitatively using transmission electron microscopy (TEM) data. With sufficiently thick barriers, quantum well layers grown on the nonplanar substrate self-order to form vertical arrays of QWRs having identical size and shape. Modeling of the QWR subbads based on TEM cross sections of the structure yields subband separations of 45, 11 and 30meV for electrons, heavy holes and light holes, with effective wire width of 9.5nm for electrons. Photoluminescence excitation spectra show enhanced absorption at the QWR subbands at temperatures as high as 200K (kBT=17.2meV) with observed electron-heavy hole subband separation of ~50meV, in good agreement with the model.
A High Performance Electronically Addressed Spatial Light Modulator
Authors: Vass D.G. , Underwood I. , Sillitto R.M. , Bradford G. , Fancey N.E. , Al Chalabi A.O. , Birch M.J. , Crossland W.A. , Sparks A.P. , Latham S.G.
Published: February 2023

It is well accepted that Spatial Light Modulators (SLMs) of suitably high performance are key components for the implementation of many proposed optical systems. We perceive that the hybrid technology of Ferroelectric Liquid Crystal (FLC) over VLSI silicon shows promise in the medium term for the development of High Performance SLMs (HPSLMs); this perception is based on (1) the performance of custom VLSI silicon (2) the large number of LC types offering a range of optical properties and their compatibility with VLSI silicon drive voltages and (3) results we have obtained, to date, of marrying the two technologies.
Experimental demonstration of a dynamic holographic memory
Authors: Qiao Yong , Psaltis Demetri
Published: February 2023

3-D dynamic holographic memories store information in volume holograms and allow selective erasure and rewriting. Photorefractive materials are a good candidate for dynamic holographic media in such memories. A basic problem with photorefractive holographic memories is that reading/writing/erasure of a certain hologram will also affect other stored holograms. A solution to this problem is dynamic copying [1-3]. We report here the experimental demonstration of a new dynamic photorefractive holographic memory that features simple architecture, phase coherence of holograms, system stability, and high restored diffraction efficiency. The memory system consists of a single photorefractive crystal for holographic storage and a feedback loop with a liquid crystal light valve (LCLV). The LCLV performs image amplification and thresholding. The basic idea is to reconstruct the stored weak hologram, amplify and binarize the reconstructed image with the feedback loop, and rejuvenate the ored hologram with the amplified reconstructed image as the signal beam. Both the input and the signal reconstructed from the hologram are imaged onto the writing side of the LCLV and read out from the other side. The system is stabilized by sampling the image read out from the LCLV using an array illuminator. When the reconstructed image is fed back to the writing side of the LCLV. each pixel is magnified slightly so that it is less likely to miss the reading-side pixel. Therefore, image shift due to misalignment or perturbation is corrected. Multiple holgrams are stored by scanning the angle of the reference beam. Detailed analysis and experimental results will be presented at the conference.
Observation of the photorefractive effect in vanadium-doped ZnTe
Authors: Ziari Mehrdad , Steier William H. , Ranon Peter M. , Klein Marvin B. , Trivedi Sudhir
Published: February 2023

We report on the first observation of the photorefractive effect in ZnTe. The photorefractive response was observed over the broad wavelength range of 0.6-1.3 μm, and suggest ZnTe to be a good candidate for semiconductor laser applications around 0.8 μm. The sample we investigated was doped with a starting vanadium concentration of 1019 cm-3 and was grown by physical-vapor-transport (PVT). The absorption tail of this sample extended from the band gap around 0.55 μm to beyond 1.5 μm. Photoluminescence studies at 5 K showed broad peaks around 1.6, 1.065 and 0.825 eV. Two beam-coupling measurements at 0.63 μm suggest an effective trap density of 1.4 x 1014 cm-3 and a value of 4.3 pm/V for the ξr41 value, where r41 is the electrooptic coefficient and ξ is the electron-hole competition factor. The photorefractive response time of ZnTe is fast; we have observed a grating formation time of 15 μsec at 4.7 W/cm3 (λ=0.63 μm) which is comparable to GaAs at 1.06 μm. The intensity dependence of the response time was sub-linear which, together with the photoluminescence spectra, suggests that multiple levels are taking part in the photorefractive effect.
Theory of Ultrafast Nonlinear Refraction in Semiconductor Lasers
Authors: Sheik-Bahae M. , Van Stryland E.W.
Published: February 2023

Recent observations of a large and ultrafast (<100 fs) nonlinear refraction in semiconductor lasers near their transparency edge has generated much interest owing to their potential use for all optical switching.[1,2] The mechanisms responsible for such nonlinearities have been partially attributed to virtual interband transitions (AC Stark effect). We have extended an earlier model [3] which successfully described the dispersion and band-gap scaling of the electronic n2 in passive semiconductors in their transparency range (hωEg). This simple model uses a nonlinear Kramers-Kronig transformation to obtain n2 from a nondegenerate absorption spectrum as calculated using a "dressed state" formalism accounting for the effects of two-photon absorption, electronic Raman, and the optical Stark shift of the bands. In extending this model to active semiconductors, it is essential to include the Fermi-Dirac (FD) distribution with quasi-Fermi levels and T2 broadening of these levels. In addition, assuming that upon Stark shifting the bands, the FD distribution re-establishes in a time τe-e ≅ 10-14 sec shorter than the pulsewith, an enhancement of n2 at the transparency point is predicted. Fig.1 depicts the calculated values of n2 for AlGaAs (Eg ≅ 1.5 eV) as a function of the photon energy for various quasi-Fermi levels. It is seen that n2 reaches a maximum negative value near the transparency point of each curve. Semiconductors with smaller band-gaps will exhibit a larger nonlinearity since n2 scales as Eg-4 as in the case of a passive medium.[3] The sign and magnitude of n2, as predicted by this theory, is in good agreement with the experimentally reported values in AlGaAs [1] and InGaAsP [2] diode lasers.
Generation of transform-limited 32 femtosecond pulses from a self mode-locked Ti:sapphire laser
Authors: Huang Chung-Po , Kapteyn Henry C. , McIntosh John W. , Murnane Margaret M.
Published: February 2023

By optimizing the intracavity dispersion compensation in a self-modelocked Ti:sapphire laser, we have generated near transform-limited pulses of 32 femtosecond duration. Our system consists of a Spectra-Physics model 3900 Ti:sapphire laser, modified by extending the cavity length and adding intracavity prisms to compensate for dispersion. Even when the prisms are adjusted for optimum compensation, a residual third-order dispersion term (a quadratic chirρ) (originating primarily from the prisms) cannot be exactly compensated. However, by proper choice of prism material, the third-order dispersion can be minimized to improve the performance of the laser. Our choice of LaFN28 prisms, spaced 53 cm apart, results in a reduction by a factor of ~2 in cubic term over the SF- glass prisms typically used. The laser produced pulses of 32 fs duration with a bandwidth of 22 nm @ 810 nm. This yields a time-bandwidth product of .32, within 5% of that for an ideal sech2 pulse. An extracavity prism pair was used to compensate for dispersion of the pulse through the output coupler and autocorrelator optics. Output power from the laser was 320 mW using 6 Watts pump power.
Flight Test of a Rocket-borne XUV Imaging Detector
Authors: Kalata K. , Golub L.
Published: February 2023

We have constructed and successfully flown an intensified CCD camera operating at XUV wavelengths. The camera is an 800X493 CCD, fiber-optic coupled to an inverting microchannel plate intensifier. XUV sensitivity is achieved by evaporating a thin layer of TPB phosphor onto the front of the intensifier; an Aluminum overcoat reduces the visible light sensitivity. This camera is flown on a NASA sounding rocket and provides real-time images of the Solar corona during the rocket flight via telemetry transmission to the ground station. Both the intensifier gain and the CCD integration time are adjustable by telemetry command during observations. The system is being used to image 304 A wavelengths, using a multilayer mirror (coated by Dr. T. Barbee, LLNL). Photon flux in-flight- is in the range 109 -1010 ph/sec over the active area, providing images with good signal-to-noise in integration times of app. 1/8 second.
Results from Flights of an X-ray Multilayer Telescope
Authors: Golub L. , Nystrom G. , Spiller E. , Wilczynski J.
Published: February 2023

An improved version of out rocket-borne x-ray telescope was flown on 22 Feb. 1991 and is presently scheduled to fly again on 11 July 1991, for studies of the Solar x-ray corona. The telescope consists of a large (25 cm. diameter) aspheric mirror, coated with a Co-C multilayer to provide x-ray reflectivity at 63.5 A. Data are recorded on Kodak Technical Pan film; up to 40 exposures, varying from 1 sec to 60 sec duration, are obtained during the five minutes of available Solar fine pointing. They improvements made to the telescope since 1989 include: 1) a new mirror and multilayer coating for improved reflectivity; b) rediesigned mirror mount to increase active area available; c) improved visible light-blocking filters with higher x-ray throughput. The overall increase in sensitivity is about a factor of three, and the spatial resolution obtained until now is of order one arcsecond. We will present results from the February flight and, if available from the July flight as well.
Perturbative integral expansion analysis of volume holograms
Authors: Lee Hyuk
Published: February 2023

Volume holograms have been widely used for high-density storage media and interconnections. Analysis of light diffraction from volume index gratings is important in obtaining storage and interconnection capacity limited by crosstalks caused by many superposed gratings. Until now, coupled-mode theory has been used to study light diffraction from volume gratings. However, as the number of index gratings increases, the coupled-mode equations become so complicated that it is impractical. To solve this problem, an integral equation method was proposed and it was shown to be adequate for a large number of volume index gratings. However, in the previous analysis, only TE polarizations and coplanar light and index grating wavevectors were studied. This eliminated the possibility of polarization mixing and it can not be used in real situation. In this talk, we present the results of perturbative integral expansion analysis of volume holograms which can be applied to arbitrary interaction geometries.
Photon noise and contrast-based visual adaptation
Authors: Rudd Michael E.
Published: February 2023

A model of signal detection based on an idealized neural contrast detector is described. The neural mechanism spatially sums photons according to a receptive field weighting function that subtracts out the dc stimulus level. The statistics of photon absorptions are taken into account, so that the time-integrated receptive field output is treated as a random variable. In the most general case, this variable is power law transformed. When the resulting variable exceeds a fixed neural threshold, a neural spike is generated. We investigate the performance capabilities of an ideal observer who monitors the spike train of a single neural mechanism which is ideally scaled and retinally located for detecting a flash of luminance ΔL, area A, and duration T, superimposed on an adapting field of luminance L. At any stage in this process, the noise in the system can be multiplied and/or added to by a constant amount of internal noise, without loss of generality. For large L, most of the variability in the spike interarrival times is a result of photon noise. For small L, internal noise dominates. Further assuming judgments based on a fixed number of spikes, the model correctly accounts for the shapes of TVI curves—including absolute threshold, a deVries-Rose region, an asymptotic Weber region—and their dependence on flash area and duration. Many properties of the time course of visual response are also accounted for. These include data concerning visual reaction time, persistence, temporal adaptation, and brightness transients.
Human efficiency in the use of shape cues in object recognition
Authors: Tjan Bosco S. , Legge Gordon E. , Braje Wendy , Kersten Daniel
Published: February 2023

How useful are different visual cues in object recognition? An answer to this question depends on the inherent information content of the cue and the effectiveness of humans in using this information. We have developed a method to measure the efficiency (as defined by signal detection theory) with which humans use information conveyed by visual cues in object recognition. The stimuli were four 3-D objects (brick, cone, cylinder and pyramid) seen from any of eight viewpoints. The objects were rendered in orthographic projection in two conditions: (1) as silhouettes (white on a dark background), in which the bounding contour was the only cue to object shape; or (2) with flat shading, which provided surface structure for object recognition. Static Gaussian luminance noise was added to the images, and the signal-to-noise ratio was set so that subject’s performance was not at ceiling or floor. In a trial, the subject was required to name the object. Overall, efficiencies were quite low, less than 1%. Efficiencies were significantly higher for shaded images than for the silhouettes. These two results may imply that shading is used primarily to extract internal contours. This possibility can be tested by measuring efficiency for recognizing line drawings of objects.
Holographic lens design using the contact screen method
Authors: Peng Fenglin , Awwal A. A. S. , Karim M. A. , Liu H. K.
Published: February 2023

For designing a hololens, we utilize the fact that the Fourier transform of a cosine grating is a pair of delta function. The spacing between the delta function is a function of the frequency of the cosine grating. By adding several cosine frequencies together one can simulate the function of one-to-many fixed interconnection network. However, in an amplitude grating the negative transmittance values are thresholded to zero. As a result, a 32-point DFT calculation reveals that the weights of the different harmonics are not equal. The sampled values are adjusted by trial and error, so that the first five orders of the Fourier transform are equal. Thus it will provide an interconnection between one input to 11 × 11 output places; earlier work has shown 5×5 connections. Next, a mask created with contact screen method that has a period of 150 LPI, and the duty cycle of the white area with respect to the total length is 1:32. Using thirty-two samples of discrete gray levels, a contact screen is fabricated using Agfa- Gevhart millimask HD plates. The fabricated grating is then tested on an optical Fourier transform setup.
Diffraction by metal strip gratings in the visible and infrared spectral regions
Authors: Schimert T. , Rasul M.S. , Magnusson R. , Wang S. S.
Published: February 2023

Experimental and theoretical diffraction characteristics of aluminum strip gratings on ZnSe and ZnS substrates in the visible and infrared spectral regions are presented. The grating thicknesses vary from 2400 to 9500 Å with a grating period of 3 μm. In the visible and near-infrared regions the gratings exhibit multiple diffracted orders. Diffraction efficiency measurements were made for both transmitted and reflected orders. The measurements are compared with results calculated with coupled-wave theory. The grating thickness and width are varied around the nominal measured values to obtain the best agreement between theory and experiment. These altered thicknesses and widths are also used in the calculation of transmittance as function of wavelength (7-13 μm) in the far IR region where only zeroth-order waves propagate. Reasonably good agreement is found between theory and experiment in these two wavelength regions using a single set of grating parameters and accounting for the wavelength dependence of the refractive indices. Furthermore, the diffraction efficiency variation as a function of grating thickness for different grating duty cycles and for different lossy materials was studied. For low-loss strips, the diffraction efficiency of the forward and backward diffracted orders oscillates rapidly with increasing grating thickness (0-5 μm). As the loss in the strips increases, the backward diffracted orders continue to oscillate whereas the forward diffracted waves stabilize.
ZA: a program for accessing ZAPP/PC data files
Authors: Vozenilek E. F.
Published: February 2023

The ZAPP/PC system records interferograms through a video frame grabber. Its processing options include the ability to record binary files that contain video intensity data, fringe center locations, wavefront phase maps on a uniform grid or Zernike coefficients. A utility program, called ZA, was developed at SGT to allow additional data processing capabilities. ZA allows the user to access all the ZAPP/PC binary file types for processing on an IBM compatible personal computer that has EGA or VGA color graphics capability. ZAPP/PC software is not needed for this off-line processing. Video intensity files and phase map files can be displayed in false color on the computer monitor, including all file identification fields. An option is provided to store the phase map on disk as a video intensity file, with encoded peak to valley and contour step size graphics. This file can be displayed on the ZAPP/PC TV monitor, and hard copies are produced on the video thermal printer. Phase map data are processed to provide phase gradient statistics and plots. ZA is written in MICROSOFT QUICKBASIC 4.5.
Optical interferometry with (forward) redirected phase-conjugate beams
Authors: Segev Mordechai , Yariv Amnon
Published: February 2023

We demonstrate a new type of interferometer based on interference between an image bearing beam and its forward redirected phase-conjugate reflection. This interferometer possesses some interesting features that are potentially useful. In one special case, where the optical path difference between the interfering beams is λ/4, and the input plane is Fourier transformed through an ordinary lens, our interferometer operates as an Hartley transformer for real images in the input plane. This offers realization of a variety of image processing applications by real (only) filters, and may simplify many optical pattern recognition implementations. Another use is a shift detector, which gives the accurate coordinates of a displaced object (that in the general case may be complex) with respect to the origin. Other types of mathematical operation on the input image are also possible.
Overview of technology trends in optical air data
Authors: Newman Leon
Published: February 2023

This paper provides an overview of current or recently completed research and development efforts, at United Technologies Optical Systems and other organizations, that involve the use of laser or optical systems to support aircraft flight. The system areas covered include: optical systems to measure free-stream airspeed and pressure for use as input to advanced platform air data computers; laser radar systems and passive optical systems for the remote detection of hazardous wind shear; laser radar systems for obstacle avoidance and precision navigation; and a brief overview of current activity in the area of fly-by-light.
Neodymium doped fiber amplifier in lidar detection
Authors: Salisbury Michael Stefan
Published: February 2023

The use of a doped fiber amplifier to amplify the return signal from a 1.06 μm solid-state lidar is examined. Two schemes are considered: heterodyne and direct detection. For the heterodyne scheme the signal will be amplified with the fiber amplifier and mixed with the local oscillator in a fiber optic evanescent wave coupler. Signal-to-noise ratio and overall sensitivity are evaluated for each case.
Overview of tactical and strategic defense laser radars
Authors: Temple P. A.
Published: February 2023

This paper first reviews the nature of tactical and Strategic Defense laser radar (LADAR) system requirements. This considers the function the laser radar is to perform, the physical constraints put upon the LADAR (e.g., weight, power), the impact of competing technologies (e.g., passive discrimination) and perceived state of the art in LADAR technology, and finally the decision making process that influences the funding levels for LADAR development. Next, several systems that are either currently functioning or are being developed are described. Examples from both the tactical and strategic worlds are considered. Finally, the future prospects for LADAR are considered from both the tactical and strategic standpoints.
SDI ladar program
Authors: Dezenberg George J.
Published: February 2023

This paper describes the laser radar technology program being conducted by the Strategic Defense Initiative (SDI) in support of the new Global Protection Against Limited Strikes (GPALS) and follow on missions. Concomitant efforts are developing laser radar systems, components, and data bases. Component/laser radar system development include efforts in agile optical beam steering technology, coherent CO2, and direct detection Nd: YAG laser radar systems. Investigative measurement of space deployment phenomenology are being conducted using the MIT Lincoln Laboratory’s Firepond Research Facility and specially designed payloads lofted aboard sounding rockets from Wallops Island, Virginia, into suborbital trajectories. Compact ranges are being used to make far-field, mono-and bistatic target measurements at 10.6, 1.06, and 0.53 μm.
Carrier relaxation in undoped C60 solid films
Authors: Halas N. J. , Cheville R. A. , Chibante F. L. P. , Ohno T. R. , Weaver J. H.
Published: February 2023

We have performed what we believe to be the first time-resolved absorption studies of C60 solid films. The films were fabricated by the evaporation of highly purified C60 onto a sapphire substrate in UHV conditions (<10-10 Torr) at 550 degrees C. Measurements were performed using a CPM laser (620 nm, pulsewidth <100 fsec) in a standard pump-probe transmission geometry. The excitation wavelength corresponds to excitation of carriers across the HOMO-LUMO gap of solid C60, a normally symmetry-forbidden transition in the isolated molecule. A nonexponential decay of optical transmission was observed on a picosecond timescale, with no subpicosecond transient characteristic of hot carrier thermalization. The nonexponential decay of the transmission signal is indicative of a geminate carrier recombination process, usually seen in amorphous semiconductors. The optical absorption spectrum of C60 also possesses an exponential rise at the band edge (Urbach tail), also characteristic of amorphous semiconductors. The observed carrier recombination can be theoretically described by a diffusion/neutralization model from which a diffusion length can be obtained. The theoretically obtained mobility is in agreement with conductivity measurements for undoped 60C films on insulating substrates.
Intramolecular vibrational dynamics of small organic molecules in the time and frequency domains
Authors: McDonald J. D.
Published: February 2023

A summary was not available at time of publication.
Dissociation energies and product state distributions: a new approach
Authors: Fry Edward S. , Bevan John W.
Published: February 2023

Molecules in a supersonic beam are excited to a predissociating state. By detecting only one of the fragments and specifically measuring its kinetic energy and rovibrational state, the rovibrational state of the other fragment can be uniquely determined without ever detecting the fragment. The dissociation energy of the molecule can also be determined to new levels of accuracy. The approach is based on time-of-flight techniques to accurately determine the speed and hence kinetic energy of the fragment. The rovibrational state of the fragment is determined by state specific excitation. A simple application of energy and momentum conservation then gives the dissociation energy and the rovibrational state of the undetected fragment.
Spatial fidelity of photorefractive optical correlators
Authors: David Andrew J. H. , Saleh Bahaa E. A. , Tataronis John A.
Published: February 2023

We investigate the quality of image correlation produced by a photorefractive crystal, where the forward pump contains one image and the probe contains the other. The nonlinear Kukhtarev equations, which describe four-wave mixing in a photorefractive crystal, are solved in the steady state, assuming only one grating and the effects of diffraction. We linearize the set of equations by making the assumptions that the pump beams are undepleted and that the backward pump is uniform and much larger than the forward pump. The resulting equations are solved using perturbation techniques. The conjugate image is found to be a bilinear functional of the forward-pump images, separately. These linear transformations include spread in the transverse plane, which results from the diffraction of both the pump and probe beams. Since the crystal is placed in the Fourier plane of the system, a bilinear transformation, instead of correlation, is performed.
Testing multilayer semiconductor electron wave devices using ballistic electron emission microscopy
Authors: Henderson Gregory N. , Gaylord Thomas K. , Glytsis Elias N. , First Phillip N. , Kaiser William J.
Published: February 2023

Ballistic electron emission microscopy (BEEM) has recently been developed to study the electrical properties of buried interfaces where ballistic electrons are injected into a sample using a scanning tunneling microscope. In this paper, a method is proposed that uses the BEEM technique to observe electron wave optical properties of ballistic transport in semiconductors. This method provides a three-terminal configuration for characterizing electron wave devices that overcomes many of the problems encountered in traditional two- and three-terminal techniques. Specifically, the method provides a highly collimated beam of ballistic carriers with a precisely controlled energy distribution. These carriers probe the quantum transmittance of a voltage- tunable electron wave interference device with minimal impurity scattering. A general procedure is presented for analyzing this experimental configuration based on a combination of the models used to describe BEEM and ballistic electron transport in semiconductors.
Algorithms for bioluminescence estimation
Authors: McCormick N. J. , Tao Z.
Published: February 2023

Two algorithms are compared for estimating the spatial dependence of bioluminescence using in situ measurements of the irradiance and scalar irradiance. The conservation algorithm is based on the conservation principle of radiative transfer, but it requires a separate estimation of the difficult-to-measure absorption coefficient; the two-stream algorithm incorporates additional equations to estimate the absorption coefficient and the albedo of single scattering. The algorithms have been numerically tested with fluctuations in measurements simulated with a random sampling approach. The effectiveness of the algorithms depends upon the strength of the bioluminescent source compared to the background seasurface illumination and other factors.
Scattering of a coherent light beam through an air-sea surface
Authors: Carter William H. , Duncan Donald D.
Published: February 2023

The radiant intensity and the far-field complex degree of spectral coherence for a coherent light beam incident from below and scattered from waves on an air-sea surface is calculated, assuming that the cross-spectral density function for the sea waves is quasihomogeneous. It is found that the radiant intensity is determined by the coherence properties of the sea waves, while the coherence of the transmitted beam is determined by the angular spectrum of the incident beam, if the illuminated area of the surface is much larger than the coherence area for the sea-waves on the surface.
Synchronization codes in the spatial and temporal domains
Authors: Li Yajun
Published: February 2023

A class of bar code sequences is considered, and it is shown that its autocorrelation coefficients are similar to those of the Barker codes1 which are the optimum codes for synchronization of digital communications. The proposed bar codes are optimum in the sense that their autocorrelation peak equals the number of transparent bars and the side lobe level ≤ 1. Merit factors of these bar codes are defined and calculated. The difference between the spatial and temporal codes is discussed in a consideration that the optical alignment of two objects is the synchronization of mechanical movement in the spatial domain.2
Superresolution through tomographic reconstruction in near-field microscopy
Authors: Schatzberg Alon , Devaney Anthony J.
Published: February 2023

Diffraction tomographic imaging algorithms use measurements of scattering from semitransparent objects to generate volume (2-D or 3-D) reconstructions of microscopic objects. An efficient direct reconstruction formula is imbedded in the filtered backpropagation algorithm. This algorithm, when applied on transmission scattering data, uses scattered fields within the homogeneous plan wave spectrum domain to generate quantitative reconstructions with spatial resolution of

λ
/

3

. Availability of near-field scanning probe technology will allow measurements with subwavelength resolution. These data, having evanescent plane wave spectra, contain information on the object with a resolution better than

λ
/

2

but cannot be incorporated into the filtered backpropagation algorithm in its presently known form. We present a generalization to the filtered backpropagation algorithm that uses evanescent plane wave spectra from scattering data to improve the resolution of reconstructions beyond the

λ
/

2

limit.
Acoustooptic morphological image processing with electronic feedback
Authors: Prather Dennis W. , Mait Joseph N. , Athale Ravindra A.
Published: February 2023

Morphology is an image algebra technique whereby the shape and structure of an input object is transformed by a smaller object called the structuring element. The two most fundamental morphological operations, erosion and dilation, are usually defined in terms of set operations. Alternatively they can be understood in terms of a convolution followed by a threshold. In this paper we describe an iterative acoustooptic (AO) morphological image processor. The input to the system is displayed on a 128 × 128 magnetooptic spatial light modulator, and the system utilizes an AO Bragg cell in the Fourier plane of a coherent optical correlator to generate the desired structuring element. Thresholding is performed electronically in an image processing system. The feedback necessary for multiple erosions and dilations is provided electronically via a single computer that controls both an image processing system in the output image plane and the MOSLM.
Massive holographic interconnections in a low energy optical processor
Authors: Kupiec Stephen A. , Christie David R.
Published: February 2023

A holographic plate that can produce N4 free-space optical interconnections, as proposed by H. J. Caulfield, can be incorporated into a special purpose processor. This will allow parallel calculations to be accomplished on a massive scale at a very low energy cost. The initial test system, which uses a 256 × 256-pixel spatial light modulator (SLM) as the dynamic array element and an N4 holographic plate containing multiple masks of the SLM, is designed for ease of use and effective quantitative evaluations. For this proposed system the holographic masks must be capable of 300 lines/in. resolution. Furthermore, the processing technique for the plate must provide for a minimum of scattering to reduce crosstalk. The system must eliminate as much noise and crosstalk as possible to reduce the number of error correction processing cycles. With fewer forced repeated cycles due to error correction, the average energy per calculation performed with such a system can be greatly reduced, even to unprecedented levels.
Spot-array generation and optical interconnection using birefringent crystals
Authors: Stone Thomas W. , Battiato James M.
Published: February 2023

Cascaded slabs of birefringent crystals or prisms may be used to generate arrays of spots or to interconnect emitting, receiving, or modulating devices. The input light for each slab can be unpolarized, circularly polarized, or polarized linearly at 45° to the reference plane, which is defined as a plane that contains both ordinary and extraordinary rays. The output light for a given stage is then resolved into two linearly polarized orthogonal component polarizations. The crystal in the next stage is rotated by 45° so that each linearly polarized wave from the output of the previous stage has components parallel and perpendicular to the new reference plane. This process may be repeated with each stage, doubling the number of spots to be formed. The thickness of each crystal slab stage controls the displacement of the spots it creates. All the stages may be optically contacted or cemented to greatly reduce reflections and scatter. This technique may be particularly useful for subarray generation where a sparse regular array of beams (e.g., as produced by a microlaser array with relatively wide element spacings) can be transformed into a much denser spot array with approximately the same lateral extent.
Optimization of second-harmonic generation efficiency in potassium niobate
Authors: Busse L. E. , Chun M. K. , Goldberg L. , Mizell G.
Published: February 2023

KNbO3 has been shown to be a promising crystal for second-harmonic generation (SHG) of tunable blue light by doubling of near-infrared emission of laser diodes and Ti:sapphire lasers. Although low power resonant cavity SHG has been previously described, there has been no reported systematic experimental determination of the maximum cw or quasi-cw single-pass SHG efficiency. Particularly, limitations to the SHG efficiency imposed by incomplete phase matching due to the nonuniform temperature distribution in the crystal have not been reported. Here we describe, we believe for the first time, cw and quasi-cw measurements of KNbO3 frequency doubling efficiencies as a function of the fundamental beam diameter, crystal length, and incident fundamental power. In optimum conditions, a maximum of 8%/(Watt-cm) was achieved using a diffraction-limited pump beam from a Ti: Al2O3 laser operating at 860 nm. Over 300 mW of 430 nm was measured in single pass SHG with 3.7 W of incident fundamental power. For high input powers, where the frequency doubled power was above a few hundred milliwatts, a large decrease in the SHG efficiency was observed for long pulse lengths and cw operation, because of heating of the active volume of the crystal causing incomplete phase matching.
Uses of a tunable injection-seeded β-barium borate optical parametric oscillator
Authors: Orr B. J. , Haub J. G. , Johnson M. J. , Fix A. , Schroder T. , Wallenstein R.
Published: February 2023

The performance of optical parametric oscillators (OPOs) has recently improved markedly through the use of injection-seeded single-mode pump laser sources and of new nonlinear optical materials, such as β-barium borate (BBO).1 With a BBO OPO pumped by such a source (delivering 315 mJ per 5-ns pulse at 355 nm), we attain a total (signal + idler) output pulse energy of ≥100 mJ throughout the tuning range 430 nm–2.0 µm, with maximum conversion efficiency >60% at a signal wavelength of 485 nm. This is achieved with a large BBO crystal (7 × 7 × 15 mm3, 30° cut for type I phase matching). Continuous tunability of the signal and idler wavelengths is readily achieved2 by injection seeding of the OPO cavity, at either the signal or idler wavelength, with narrowband radiation from a low-intensity tunable laser, such as a dye or diode laser. The output wavelengths are controllable over a wide tuning range (> 100 cm-1) with minimal adjustment of the angular setting of the BBO crystal, resulting in remarkably simple spectroscopic operation.