bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection volume holographic lenses with wide field of view and wavelength multiplexing
Authors: Ma Jian , Catanzaro Brian , Fainman Yeshaiahua , Lee Sing H.
Published: February 2023

Recording volume holographic lenses (VHLs) in thick (i.e., 1 mm or more) materials is attractive because it yields sufficient color selectivity to superimpose many different lenses in the same volume. However, the small field of view (FOV) of the lenses, due to the highly angular selective nature of thick holograms, has greatly limited their applications. We have developed a theoretical model that predicts general characteristics of the VHLs, such as diffraction efficiency, FOV, SBWP, and wavelength selectivity, based on Kukhtarev’s equation and coupled wave theory. We found that the FOV can be predetermined during the recording process by controlling the offaxis angle between the two counter-propagating spherical waves used to record the reflection VHLs. The FOV is maximized when the off-axis angle is zero. A variety of on-axis and off-axis lenses were recorded with different focal lengths and at different wavelengths. When these lenses are used for imaging, they can provide lateral scanning and longitudinal zooming by simply tuning the wavelength. VHLs of f/2.5 were attained. These allow an object of size 8 mm×8 mm to be imaged with the variation of diffraction efficiency smaller than 50% and without obvious aberration distortion. The wavelength selectivity of λBragg = 1.5 Å was predicted by theory and was experimentally verified by using a tunnable Ti–sapphire laser operating around 0.8 µm.
Polarizing computer-generated holograms based on liquid crystals
Authors: Hossfeld Jens , Tschudi Theo , Dultz Wolfgang
Published: February 2023

Polarizing optical elements are widely needed in modern optics. The combination of the beam shaping properties of a computer-generated hologram (CGH) with polarizing features provides a further step in integration of optical systems. We have developed a new technique to produce switchable polarizing CGHs. A microstructured glass substrate containing the hologram function is covered with a layer of NLC. The LC is oriented parallel to the substrate plane, and the lower refractive index of the LC is matched to the refractive index of the glass. Thus the hologram structure is invisible for one polarization state of light. The orientation of the LC may be changed by applying an electrical field between transparent electrodes on the substrate and the cover glass. In this case the refraction index is matched for all polarization directions. Finally, we obtain an element that serves as a CGH for one polarization direction, which does not effect the orthogonal one and which may be switched off via electrical control.
High temperature characterization of CVD diamond
Authors: McNeely J. R. , Clausing R. E. , Akerman M. A. , Snyder W. B. , Thomas M. E.
Published: February 2023

In support of SDIO objectives to develop optical quality CVD diamond windows, multiwavelength measurements of IR transmission, reflection, emissivity, and scatter are being made on samples from room temperature to 500°C. Free standing CVD diamond is compared with natural type IIa diamond of similar thickness and identical temperature. Extrinsic effects are measured in CVD windows provided by various manufacturers and laboratories but are measured under the same conditions and with the same equipment. No manufacturers will be identified. Intrinsic properties such as two-phonon absorption are compared with model predictions.
Analysis methods for aero-optical effects and thermally induced optical path distortion
Authors: Wojciechowski C. J. , Gierloff J. J.
Published: February 2023

The presentation presents two empirical methods to bridge the gap between computational fluid dynamics codes and physical optics codes. The two empirical methods that define the turbulence fluctuations and scale sizes are compared to available test data. The complete solution to several stressing Endo Leap design points are presented. The results for both external window film cooling and internal cooling are combined with the thermal gradients in the window to predict the total optical distortion. The method of obtaining optical path differences within the window is applicable to either external or internal cooling. The results of the analyses indicate that an internally cooled window has potentially no aero-optic image degradation. External film cooling causes varying amounts of image degradation, depending on the type of cooling and the flow conditions. These results agree with test data and empirical calculations. The computational fluid dynamics and physical optics codes have been in use for years and are well verified.
Model of the photon as a particle moving like a wave
Authors: Weber Paul E.
Published: February 2023

I will discuss a real imaginary photon model that has a constant energy content with its rotating elementary charges e
+
and e
-
around a common center and moving with a constant speed as a particle, wavelike through empty space. This leads to an indication that there is a difference between the electromagnetic oscillation of dipoles radiating in all direction and the single-direction rotation of the forward moving electrical potential difference of the photon, as photovoltaic and photoconductive detetcters indicate, since they can detect no wavelengths larger then 42 µm (GeZn detector). Furthermore, this photon model explains why gravitational waves, accelerating galaxies as the source of red shifts, and the universal equation E = mc2 are not possible if this model is found to be true. Here it is also explained why the rotating and forward moving charges have no magnetic field. Finally, it is shown that at a beam splitter a photon is either reflected or transmitted and why interference still occurs in an inteferometer in so-called single-photon experiments.
Gas phase emission spectra of C 6 F 6 + inert gas clusters
Authors: Yang B. , Walker B. , Breeden T. , DiMauro L. F.
Published: February 2023

Laser induced fluorescence and dispersed emission spectra of C6F6Ar
n
(n = 1–10) clusters have been studied in a supersonic freejet expansion. By controlling the expansion conditions, we can approximately mass select the clusters and selectively pump the

C
6

F
6
+

Ar

n

from the ground electronic state to different vibrational modes of the excited electronic state. We observe that the wavelength resolved emission consists of a broad (about 1300 cm-1, FWHM), Stokes shifted spectrum that is independent of vibrational excitation and indicative of condensed phase emission. This is in contrast to the LIF spectrum, which yields much narrower linewidths. The emission and excitation spectra show an increasing red shift with larger cluster size that saturates at high pressure. A model is proposed for explaining all the above phenomena. A similar experiment is also being performed with C6F6He
n
clusters.
Infrared difference frequency spectrometer for high resolution spectroscopy of molecular transients
Authors: Simon U. , Miller C. E. , Curl R. F. , Tittel F. K.
Published: February 2023

Infrared absorption spectroscopy is an effective spectroscopic technique for studying transient molecules since it combines high spectral resolution and high detection sensitivity. The recent availability of novel nonlinear materials such as AgGaS2 and AgGaSe2 makes it now possible to generate narrowband coherent radiation over a wide range (4–18 µm) by means of difference frequency generation. This letter reports on the mixing of a tunable cw dye and dye/Ti:sapphire laser system in a AgGaS2 crystal 45 mm in length. By using 90° type I phase matching, cw infrared output powers at the 50 µW level can be provided for spectroscopic application. Continuous scans of up to 1 cm‒1 width have been achieved. Transient molecules can be generated conveniently by excimer laser photolysis with an appropriate precursor. For a sensitivity enhancement a 1 m White cell with a variable optical path length of up to 60 m is employed. The signal is acquired by a transient digitizer interfaced with a computer. First spectra of molecular transients will be presented.
Discharge fluorescence spectra of S2 vapor
Authors: Zhonghua Zhang , Junhua Yu , Zhongwei Zu , Hua Zhang , Zuguang Ma
Published: February 2023

The stable self-sustained glow discharge in S2 vapor was obtained at the sulfur vapor temperature of 180–250°C in a transverse discharge quartz cell with UV preionization. The emission spectra of pure S2 is from 293.3 nm to 510.4 nm at the temperature of 230°C. Under the same condition the range of emission spectra changed to 350-520 nm when 2 Torr He buffer gas was added. This shows that the relaxation of

B
3

Σ
u
−

accrued from He buffer collision. We observed the phenomena of S2 emission spectra due to S2–S2 collision and self quenching when the S2 vapor temperature was higher than 250°C. The double-Blumlein circuit we used produced a pulse rise time of 7 ns and pulse duration of 10 ns.
Comparison of optical turbulence models for forecast applications
Authors: Freeman K. , Orgill M. , Davis R. , Endlich R.
Published: February 2023

Optical turbulence models are compared to determine which offers the most utility for producing 4- to 6-h forecasts of C
n
2 over 1-km horizontal paths. The models tested include a statistical regression model (after Sadot and Kopeika, 1992), a direct estimate of C
n
2 from similarity theory (Miller and Ricklin, 1988), a bulk model (Andreas, 1988), and a more comprehensive physical model developed for use at White Sands Missile Range (Kunkel and Walters, 1988). One important measure of success in this comparison is the ability to forecast, with reasonable accuracy, the input parameters for the selected model. The statistical model and the Miller and Ricklin model use commonly measured meteorological parameters, which are also commonly forecast. The other models require more elaborate instrumentation and computation for parameters such as soil moisture and heat and moisture fluxes, which are more difficult to forecast. Therefore, these models may not be as convenient to use. In order to assess the relative utility of the models, the paper also includes a brief look at the sensitivity of the models to the input parameters.
Optimal design of a monostatic coherent laser radar with a circular aperture
Authors: Frehlich Rod G.
Published: February 2023

The optimal laser field for the local oscillator of a monostatic coherent laser radar observing a diffuse or aerosol target given the transmitter field is the solution of an integral equation. To our knowledge, the only analytic solution published is for an unrealistic case of an aperture described by a Gaussian transmittance function. This integral equation is solved numerically for the more common circular aperture and various transmitter field geometries, including a Gaussian field and an unstable resonator field. The optimal design is compared to the optimal parameters of previous work, where the local oscillator was taken to be a Gaussian field. An optical design that generates these optimal fields will be presented. The physics of the optimal conditions will be discussed by using simulations of the signal and local oscillator fields on the detector surface. This provides a visual presentation of the optimal fields and insight into the limitations of coherent laser radar design. These new results provide a simple design for the optimal performance of the monostatic coherent laser radar.
Improving humidity and wind measurements at a high energy laser test facility
Authors: Vaucher Gail T. , Endlich Robert
Published: February 2023

Accurate humidity and wind measurements are critical when characterizing the atmosphere at a high-energy laser test facility. The 1990 General Eastern Hygrometer (1200 Series) calibration curve produced by the National Institute of Standards and Technology displayed resistance as a nonunique function of dewpoint temperature. In 1991, a revised standard calibration procedure was developed. This new procedure corrected this problem and changed the formerly 5-7°C dewpoint differential between humidity sensors to a 1°C separation. A wind tunnel calibration of seven polypropylene and six polystyrene R.M. Young Gill anemometers (Model 27106) demonstrated that the polypropylene anemometers have a 0.4 m/s separation between averaged starting and stopping thresholds; the polystyrene thresholds were less than polypropylene thresholds and well below critical cross-wind laser beam ventilation. All 13 anemometer calibration curves were unique. Combining the 13 calibration curves into one generic operational curve created an uncertainty ≤8%. Collating curves by sensor type produced uncertainties of ≤3.4% for polypropylene anemometers and ≤7.0% for polystyrene anemometers.
Moisture shift testing of thin film interference coatings
Authors: Herrmann William C. , Morton Dale E.
Published: February 2023

Laser eye protection filters exhibit a moisture shift phenomenon that must be carefully and accurately characterized. This phenomenon is the absorption of moisture in a thin film structure, causing an increase in refractive index for one or more of the materials. Once absorbed, some of the moisture is loosely bonded and can easily be driven off in vacuum or by low temperature heating. Some of the moisture is tightly bonded and can be driven off only with a high temperature bake. We have studied a series of testing techniques involving exposure of samples to vacuum, pressure, heat, and moisture or water to develop testing procedures to accurately evaluate their performance over the extremes of environmental exposure. The effect of loosely bonded moisture can be readily characterized by evaluation parts submerged in water and oven bakes at 80°C purging with dry gas. Characterization of tightly bonded moisture requires higher temperature to drive it out.
Optimal design of multilayer coatings for dual-wavelength magneto-optic data Storage
Authors: Wang Beijing , Zhao Yang , Auner Gregory W.
Published: February 2023

Optical data storage using short wavelengths (blue light) can reduce the spot area size and increase the data density by a factor of 4. A blue wavelength semiconductor laser with the necessary output power for writing information onto optical disks is not available. To increase the data transfer rates requires higher laser power because the switching of the magnetization during the writing process occurs in a proportionately shorter time period. Therefore, it is necessary to increase the efficiency of energy absorption by optical recording media so that the power requirement for writing can be reduced. However, a certain amount of reflectance is needed during reading since the reflected signal must be large enough to be detected. Applying conventional thin film coating techniques to optical data storage, we start from current available coating materials (e.g., TiO2 or ZnS) and search for an optimal multi-layer structure. The optimally designed recording medium shows different optical properties at reading and writing wavelengths. The critical design points are low reflectance at writing wavelength (λ
w
), optimal value of figure of merit at reading wavelength (λ
r
), and small difference between λ
r
and λ
w
, which results in a small wavelength tuning in a second harmonic generation system. Our computer simulations show that an appropriate multilayer coating design can not only reduce the power requirement of an optical recording system but also enhance the signal-to-noise ratio.
Subquantum limit measurements with optical pulses
Authors: Bergman K. , Doerr C. , Haus H. A. , Shirasaki M.
Published: February 2023

Squeezing of 100 ps pulses from a Nd:YAG laser operating at 1.3 μm in a fiber ring has led to a reduction of noise 5 dB below the shot noise level. This reduction occurs in a spectral window between 40 and 90 kHz, a frequency range particularly convenient for instrumentation. Guided acoustic wave Brillouin scattering (GAWBS) was found to be the process limiting our squeezing to 5 dB. The G AWBS measurements will be presented. In the meantime promising ways of reducing the GA WBS have been found and will be described. Fiber ring squeezing permits the reuse of the pump as local oscillator (in principle in full if Faraday rotators are used). A simple system of a fiber ring squeezer with an interferometer in cascade is being constructed to perform a phase measurement below the standard quantum limit. Experimental results will be presented.
Atomic spectroscopy with squeezed light
Authors: Kimble H. J. , Polzik E. S. , Carri J.
Published: February 2023

A frequency tunable source of squeezed light has been developed for application to a variety of problems in atomic physics. The basic experimental arrangement consists of a subthreshold optical parametric oscillator (OPO) that is pumped by the frequency-doubled output of a titanium-sapphire laser. Squeezed light with continuous tunability of 2 GHz has been generated with a directly observed nonclassical noise reduction of 5.0 dB relative to the vacuumstate limit in a balanced homodyne detector (5.2 dB when corrected for detector noise). Although our source is potentially broadly tunable over the noncritical phase-matching bandwidth of potassium niobate, current research has concentrated on operation at 852 nm for excitation of the D2 line of atomic cesium. Relative to the usual quantum limit associated with vacuumstate fluctuations, enhanced sensitivity is demonstrated for the detection of Doppler-free resonances in FM saturation spectroscopy, with an improvement of 3.1 dB directly observed and 3.8 dB after correction for detector noise.
Measurement of the intensity and phase of a femtosecond UV laser pulse in a single shot
Authors: Kane Daniel J. , Taylor A. J. , Trebino Rick
Published: February 2023

We report and demonstrate what is to our knowledge the first measurement of the intensity and phase of a single femtosecond UV pulse. The technique, which we call frequency resolved optical gating (FROG), is inexpensive, easy to implement, and provides an output that graphically displays the instantaneous frequency vs. time of the pulse. It uses the well-known polarization-spectroscopy optical-gate arrangement with an instantaneously responding χ(3) sample medium such as quartz. Here, however, the pulse gates itself. The signal spectrum is then measured as a function of delay between the two input pulses. Because the gate is shorter than the input pulse, it reveals, for a given delay, the frequency of a particular temporal component of the ultrashort pulse. For reasonably well-behaved pulses, the output plot of intensity vs. frequency and delay graphically displays the pulse instantaneous frequency vs. time.
Strained GalnP/AlGaInP quantum well diode lasers
Authors: Geels Randall S. , Bour David P.
Published: February 2023

Visible AlGaInP lasers are under investigation for applications including pumping of Cr3+ doped solid-state lasers, photodynamic therapy, optical recording, printing, scanning, and He-Ne laser substitutes. Recently structures with strained quantum well (QW) active regions have improved the performance of AlGaInP lasers for higher power, shorter wavelength, and lower threshold current. In spite of the relatively low conduction band offset in GaInP/AlGaInP heterostructures, threshold currents and characteristic temperatures (T0) are approaching values typical of GaAs/AlGaAs lasers.
Surface-relief hologram reproduction
Authors: Eguchi Shin , Yamagishi Fumio
Published: February 2023

One of the factors determining the diffraction efficiency of the grating of a surface-relief hologram is the refractive index of the material. The refractive index of the photopoly­mer constituting a reproduced grating is smaller than that of the photoresist constituting the master grating. To reproduce the grating with a high diffraction efficiency, we studied how to optimize the grating shape. We found that a grating 0.5 μm wide required a master grating 0.9 μm wide to get the highest diffraction efficiency and that the reproduced grating had to be at least 1 μm deep. We fabricated a master and stamp and replicated gratings with a diffraction efficiency of 78 ±5%.
Errors in diffractive optic fabrication
Authors: Lanteigne David J.
Published: February 2023

Fabrication errors in the manufacture of a binary optic may arise both from limitations of the pattern generator and from limitations inherent to the lithographic or etching process. The fabrication of a whole series of simple diffraction gratings patterned with a Mann device are used to determine jitter and systematic errors in the pattern generator. The diffraction behavior of the final optic is tested for deviations from perfection by comparing it to the diffraction calculated from an electromagnetic diffraction code.
Automatic target recognition using a feature-based optical neural network
Authors: Chao Tien-Hsin
Published: February 2023

An optical neural network that is based on the neocognitron paradigm proposed by K. Fukushima is implemented and experimentally demonstrated for automatic target recognition. A novel aspect of the optical architectural design is the use of a shift-invariant multichannel optical correlator within each processing layer. Multilayer processing is achieved by iteratively feeding back the output of the feature correlator to the input spatial light modulator and updating the Fourier filters. Characteristic features are first extracted from the object images as the training set. Neural synaptic weights are stored in Fourier hologram array. Distortion invariance is greatly improved with the use of these training features. As an example of experimental demonstration, simulated reentry vehicle and decoys image are used as the test objects. Successful recognition and classification of these objects with intraclass fault tolerance and interclass discrimination is achieved. A detailed system description and experimental demonstration are presented.
Optimal control of quantum dynamical systems
Authors: Rabitz Herschel
Published: February 2023

A long-sought-after goal in chemistry and physics has been the desire to externally control and manipulate molecular dynamical processes governed by the laws of quantum mechanics. Although optimal control theory is widely used in many engineering disciplines, it has only recently been recognized that these concepts are applicable to the design of controllers (e.g., external optical fields) for manipulating molecular scale events. The theoretical concepts of quantum mechanical optimal control theory will be reviewed and illustrated with realistic computations. The prospect of teaching lasers in the laboratory to control molecules will also be discussed.
Clusters containing open-shell molecules
Authors: Miller Terry A.
Published: February 2023

Bonding between atoms and molecules can span wide extremes. Long, weak van der Waals bonds, e.g., between closed-shell inert gas atoms, at least in principle can be characterized in terms of multipolar interactions between separated charge distributions. Short, strong chemical bonds, e.g., between open-shell radical species, must be described in terms of delo­calization of the initial electronic distributions. We have recently begun to experimentally characterize complexes formed between one open- and one closed-shell species. Systems studied include inert gases (and some metal atoms) bonded to a series of radicals including OH, CdCH3, cyclopentadienyl, and hexafluorobenzene cation radicals. These results will be discussed in terms of both the unusual bonding present and, in some cases, the evolution of simple complexes to the condensed phase limit.
New opportunities with coherent soft x-rays
Authors: Attwood David
Published: February 2023

Bright, partially coherent sources in the 20-200 Å wavelength region, combined with new developments in lenses and mirrors, have opened new opportunities for microscopy in the life and physical sciences. We describe the development of diffractive lenses that discern 300 Å features at wavelengths from 24 to 45 Å, interference coatings that achieve 60% normal incidence reflectivity at 130 Å wavelength, undulator radiation that provides broadly tunable partially coherent radiation, and soft x-ray lasing that has been used for high resolution subnanosecond imaging. Applications include biological microscopy of structures at the border between the largest macromolecules and the smallest organelles, element-specific and chemically sensitive studies of surfaces and thin films on spatial scales of less than 1,000 Å, and x-ray optical pattern transfer techniques relevant to the manufacture of future nanoelectronic devices. Further opportunities based on soft x-ray coherent optical techniques, two-photon pump-probe techniques, and combination techniques that might permit element-specific atomic resolution scanning tunneling will be discussed.
Experiences in making DUV lithographic objectives
Authors: Zernike F.
Published: February 2023

Since only fused silica can be obtained with good enough homogeneity, most lithographic objectives for use below 300 nm are only corrected for very narrow wavelength ranges. As a result these objectives have to be used with wavelength narrowed excimer lasers. By going to catadioptric objectives both high N.A. and moderate chromatic correction can be obtained, still using only one material. A first such objective was built for use with a mercury source at 248 nm. A second objective is being built for use with an argon fluoride laser at 193 nm. The design and the methods used in building these objectives will be described.
Multilayer reflection coatings for soft x-ray projection lithography
Authors: Stearns D. G. , Rosen R. S. , Vernon S. P.
Published: February 2023

We describe the current approaches for depositing high performance multilayer (ML) coatings on large area figured optics by using dc magnetron sputtering. The highest normal incidence reflectivity of 66% at 130 Å has been achieved by using ML composed of alternating layers of Mo and Si. The optimum structure, corresponding to smooth pure layers separated by narrow interlayers of mixed composition, is obtained by sputtering at low Ar pressure of 1.75 mTorr. In magnetron sputtering at low Ar pressure the energy flux is provided by the reflected Ar neutrals. However, we have observed that high quality ML can also be grown at higher Ar pressure (10 mTorr) by applying a dc bias to the substrate, thereby extracting Ar ions from the plasma that bombard the growth surface. Excellent coating uniformity has been achieved by implementing a combination of large area sources, small source-to-substrate separation, and compound planetary motion of the substrates. This approach requires no masking to generate a uniform deposition profile, which significantly simplifies the accommodation of different targets, substrates, and deposition conditions. Furthermore, since the intrinsic deposition profile is uniform, simple masks can be used to produce axisymmetric variations in the ML period when laterally graded coatings are required.
Status and a future vision of optics in New Mexico
Authors: Conway Bruce
Published: February 2023

Summary not available at press time.
InAsSb structures for III–V based infrared optoelectronics
Authors: Kurtz Steven R.
Published: February 2023

The electronic properties of InAsSb structures have been characterized by a variety of infrared spectroscopies (absorption, photoluminescence, and magneto-optical) and detector spectral responsivity. In Sb-rich strained-layer superlattices (SLSs), the type II band offset extends the photoresponse to long wavelength when the difference in As composition between SLS layers is 10–20%. Consistent with a type II offset, effective mass measurements reveal that the hole quantum well is located in the biaxially compressed InSb layer of an InAsSb/InSb SLS. As an alternative to Sb-rich, InAsSb SLSs for long wavelength III–V detector structures, we have recently observed significant band-gap reduction in InAs1−
x
Sb
x
(x ≈ 0.4) alloys and SLSs. Ordering on the {111} planes of the group V sublattice (CuPt-type) produces this decrease in band-gap. Prototype infrared detectors and focal plane arrays have been constructed from Sb-rich SLSs. Our best photodiodes were 300 K BLIP limited with detectivities ≥1 × 1010 cm Hz1/2/W at wavelengths <10 μm. Prototype detector studies demonstrate that InAsSb SLSs could potentially compete with HgCdTe as a high detectivity, long wavelength photovoltiac detector technology.
An efficient 1.3 μm TE/TM splitter by K+–Na+ ion exchange
Authors: Miliou A. , Srivastava R. , Ramaswamy R. V.
Published: February 2023

TE/TM polarization splitters are important devices in optical communication systems. Fabrication of such devices requires birefringent waveguides. As a result, Ti:LiNbO3 is used in real situations in spite of the associated complex waveguide fabrication technology and the inherent fiber incompatibility. Glass waveguides are attractive for economic reasons and for fiber compatibility. In this work, we report a glass waveguide polarization splitter for operation in the 1.3 μm wavelength region. The device, which has a symmetric directional coupler configuration, exploits the rather large stress-induced birefringence in K+–Na+ ion exchanged waveguides, giving rise to an adequate difference in the coupling lengths for the two polarizations. Starting from the measured potassium concentration (refractive index) profile of the structure and utilizing a combination of the multilayer stack theory and the effective index method, we calculate the normal mode propagation constants and mode-field profiles to determine the polarization splitting length and the extinction ratio and, for the first time to our knowledge, compare the results with the experimental data. It is shown that in a given coupler the splitting occurs at several wavelengths in the 1.0–1.45 μm range. A 22.5 mm long coupler, fabricated by thermal diffusion of K+ ions in BK7 glass, exhibits an extinction ration of 18.2 dB, in excellent agreement with the simulation results.
Room temperature upconversion lasers in rare-earth doped crystals
Authors: Thrash R. J. , Johnson L. F.
Published: February 2023

Diode laser pumped, room temperature upconversion lasers are one possible route to ail solid-state visible wavelength laser devices. Room temperature, upconversion laser operation has been obtained by using barium yttrium fluoride doped with either thulium or erbium ions, and sensitized with ytterbium. The 960 nm output from a titanium sapphire laser or diode laser serves as the pump source. Excitation is accomplished by means of energy transfer from ytterbium to the active ion. Successive transfers of energy from ytterbium to the active ion, as well as cross-relaxation processes among the active ions, distribute the energy to the various excited states responsible for the laser emission. Laser operation has been obtained at wavelengths in the red, green, and blue regions of the visible spectrum. Several of these transitions are capable of cw operation. A discussion of the pumping processes and recent results will be presented.
Cooperative upconversion lasers and nonlinear dynamics
Authors: Rand S. C.
Published: February 2023

Here we describe a class of cw upconversion lasers in which inversion is due exclusively to cooperative interactions of rare earth ions in highly doped solids, resulting in unique opportunities for output wavelength agility, large upconversion factors, and high quantum efficiencies through nonlinear dynamics. We have isolated capabilities of the cooperative mechanism by performing experiments in Er:CaF2 and Er:LiYF4 with infrared pumping of the first Er3+ resonance at 1.53 μm. At liquid helium temperatures, laser action at 544 nm was achieved in an astigmatically compensated, three-mirror cavity with 5% efficiency in LiYF4. The upconversion factor (ratio of pump to laser wavelength) was 2.81, to our knowledge the highest ever reported for cw upconversion lasers. At 77 K, laser action at 551 nm was observed. Surprisingly, output at both 544 and 551 nm was truly cw with cooperative pumping, unlike earlier green erbium lasers, which exhibited self-pulsing. Also at 77 K, near infrared laser action was obtained at 0.855 pm with exceptionally high efficiency in CaF2(28%) and LiYF4 (20%) on self-quenching transitions. Successful demonstration of cw laser action on such transitions also suggests a means whereby quantum efficiencies may exceed unity. The lower laser level in such cases is the origin of cooperative pumping to the upper laser level, but also receives population as the result of stimulated emission. Hence population can be recycled for enhanced quantum efficiency. Additionally, population pulsations can occur and sustained oscillations in laser output have been observed in a cooperative erbium upconversion laser at 2.8 μm.
Visible to UV up-conversion luminescence from Er3+ doped crystals of CsMgCl3
Authors: Gharavi Ali , McPherson Gary L.
Published: February 2023

Strong UV emission has been observed in crystals of CsMgCl3 doped with Er3+ ions when pumped with 546 to 550 nm wavelengths. CsMgCl3 crystals exhibit a chain structure where two Er3+ ions replace three Mg2+ ions in the chain, preserving the local charge balance forming discrete defined pairs. The UV emission is observable at temperatures between 10 and 297 K. At 10 K the intensity of the UV emission is comparable to the emissions from the pumped state. The experiments performed in our lab show that the up-conversion is a second order process due to energy transfer between simultaneously excited Er3+ pairs involving two 4S3/2 states, raising the energy of one Er3+ sight to twice the energy (4G9/2). Energy migration through the crystal and other doubly excited pairs also results in weak up-conversion emissions. The strongest UV emissions are due to transitions from 4G9/2 to 4I13/2(338 nm) and 4G11/2 to 4I13/2 (377 nm). Because of thermal population of the sublevels within the ground state (4I15/2) manifold, a number of red shifted features (hot bands) appear in the excitation spectrum as the temperature is raised from 10 to 297 K.
Spectroscopic and laser properties of Nd3+ in CaF2 and YLF
Authors: Sardar D. K. , Velarde-Montecinos R. C.
Published: February 2023

Optical absorption and emission intensities are investigated for trivalent neodymium ions in single crystals of CaF2 and YLF. Oscillator strengths for numerous transitions are measured from absorption spectra recorded at room temperature. Corresponding oscillator strengths are calculated by using the Judd–Ofelt theory and are compared with the measured values. A least-squares fitting of the measured and calculated line strengths of the absorption spectra yields the values of the phenomenological intensity (Judd–Ofelt) parameters Ω
2
, Ω4, and Ω6 for the chosen ionhost combinations. The Judd–Ofelt parameters are also used to calculate the spontaneous emission probabilities, radiative decay rates, and branching ratios from various excited levels of Nd3+ that fluoresce in CaF2 and YLF. Finally, the spectroscopic quality factors, which are defined as the ratio of the intensity parameters (X = Ω4/Ω6), are computed and compared with those for other Nd3+-based laser materials.
Dynamics in floppy molecules
Authors: Spangler Lee H.
Published: February 2023

The effects of skeletal vibrations, substitution, and van der Waals complexes on barriers to methyl torsion and/or nitrogen inversion are presented.
Effects of external and internal electric fieds on ultra-narrow photochemical holes
Authors: Kohler Bryan
Published: February 2023

Summary not available at press time.
Optical detection and characterization of transition metal containing molecular beams
Authors: Steimle Timothy C.
Published: February 2023

The most insightful molecular information comes from the analysis of optical spectra recorded at a resolution sufficient to resolve splittings associated with the fine interactions (rotational, spin–rotation, etc.), hyperfine interactions (Fermi contact, quadrupole, etc.), and the application of external fields (Stark and Zeeman). In the case of freely rotating metal containing polyatomic molecules this requires the combination of a “cold” molecular beam sample preparation, spectral resolution of cw-dye laser excitation, and the sensitivity of laser induced fluorescence. A review of our application of these approaches to diatomic and polyatomic metal containing compounds will be given. A comparison of the applicability of conventional effusive ovens to produce “hot” molecular beams, with laser ablation/reactant and “pickup” methods used to generate “cold” beams will be made. The spectroscopic techniques described include optical Stark LIF and microwave-optical double resonance using the pump/probe detection scheme (MODR-P/P). The MODR-P/P is particularly useful in complex molecular systems because it exploits the sensitivity of LIF detection, while probing only the ground electronic state. We have demonstrated that this technique is compatible with the laser ablation/reactant scheme. The molecular systems to be considered are transition metal oxides and the alakaline earth monocynides.
Interaction of first- and second-order processes in 2D motion perception
Authors: Wilson Hugh R.
Published: February 2023

Recent psychophysical experiments have shown that the perceived direction of motion of plaids, composed of two cosine gratings moving in different directions, can deviate by up to 50° from the true direction of rigid translation. We have developed a dynamic neural network model that predicts these and other motion data. The model incorporates two motion pathways that are subsequently combined by using a vector sum operation. The first motion pathway extracts the directions of motion of the component gratings, i.e., the Fourier motion signals, while the second pathway employs filtering and full-wave rectification to extract a non-Fourier motion signal. The vector sum of these motion pathways quantitatively predicts the psychophysical data, and it explains the existence of parallel input pathways from both V1 and V2 to area MT. The model correctly predicts that non-Fourier plaids will move in the vector sum direction, and interactions across spatial scales in the model accurately predict transitions from rigid to transparent motion.
Enhancement of the photorefractive gain in CdTe at 1.3-1.5 μm under alternating electric fields
Authors: Ziari Mehrdad , Steier William H. , Ranon Peter M. , Klein Marvin B. , Trivedi Sudhir
Published: February 2023

CdTe:V is a photorefractive material with high theoretical and measured sensitivities at wavelengths from the band edge (0.9 μm) to 1.5 μm. We report large enhancement of the two-beam-coupling gain in V-doped CdTe by using the applied alternating field method with square and sinusoidal wave forms. With nominally square wave forms, gain coefficients in excess of 10 cm−1 have been measured at 1.3 μm wavelength, which significantly exceed the absorption coefficient of 2 cm−1 in our sample. We have studied the effects of the ac voltage pulse shape using nominally square waves in the 100-230 kHz range and sinusoidal fields in the 3-7 MHz range. The exact shape of the internal electric field is measured by using the electro-optic field-induced birefringence and suggests a fast screening of the internal field. We will present a model that discusses the major effects of the alternating waveform shape and internal field screening on the beam-coupling gain. We have also measured the dependence of the gain on the pump-to-signal beam ratios and will present the results for both square and sinusoidal waveforms. Our observations suggest that large gain values are only attainable at very large beam ratios for the case of square waves.
Specially doped LiNbO3 crystal hologram using low power laser diode
Authors: Yin Shizhuo , Yu Francis T. S.
Published: February 2023

We present results of using a low-power laser diode to record a real-time hologram in a specially doped LiNbO3 crystal in this paper. The important aspect of this specially doped photorefractive crystal is that the sensitivity to red light is several orders higher than that of the conventional crystals, for which it makes the construction of a crystal hologram by using a low power, small size, and low cost laser diode possible. One of the major disadvantages of using the currently available crystals to record holograms is the high power requirement of the light source. Since the low power diode laser is used for the writing and the reading processes, the specially doped crystal hologram can last much longer than that of a high power laser. In the experiments, a 10 mW laser diode with an output wavelength of 670 nm is used. Our results show that very good reconstructed images can be obtained by using a simple diode laser. Because of the low- power requirement, this specially doped crystal would have a significant impact on many practical applications, namely, optical interconnections, switching, etc.
Soft x-ray imaging of biological materials at Los Alamos National Laboratory
Authors: Guttmann G. D. , Cobble J. A.
Published: February 2023

Soft x-ray contact microscopy (SXCM) is a form of x-ray lithography; however, the biological cell is imaged. Imaging of the biological sample is by soft x- rays within the "water window," which has an energy range of 277–525 eV. The contrast mechanism is based upon the x-ray absorption lengths of carbon and nitrogen, which are ~10 times shorter than that of oxygen in the "water window." In previous experiments at the Lawrence Livermore National Laboratory PHOENIX laser facility, the major result was the first high-resolution (~30 nm) x-ray micrographs of living mammalian cells, CHO-SC1. One of the images showed chromosomes in the mitotic stage. Future efforts at Los Alamos National Laboratory will be the utilization of the Free Electron Laser and in-house laser-produced plasmas as x-ray sources, the use of atomic force microscopy to read the resists, the development of thin window technology and resist applications, the use of multilayer and Fresnel zone plate x-ray optics for holographic purposes, and the use of biological agents to enhance the x-ray images of key cellular structures. Biological studies will look at the structure of chromosomes and chromatin in the living cell.
Ultra-high internal (99.7%) and external (72%) spontaneous emission quantum efficiency from a GaAs/AlGaAs double heterostructure
Authors: Schnitzer I. , Yablonovitch E. , Caneau C. , Gmitter T. J.
Published: February 2023

It is now clear that the internal spontaneous emission quantum efficiency (η) needs to be close to unity in order to reduce the photon-number noise in semiconductor lasers below the classical limit and in order to demonstrate single- mode (thresholdless) LED operation. We use a novel method for measuring 1−η and conclude that in a high quality GaAs/AlGa As double heterostructure η can be as high as 99.7%. Our GaAs/AIGaAs double heterostructure is separated from the absorbing parent substrate by using the epitaxial liftoff technique and is then mounted on a reflecting substrate. The idea is that spontaneously emitted photons are sent into free space where they can be measured, internally absorbed and reemitted, or absorbed and dissipated to heat in the surroundings. We show that in our configuration the external quantum efficiency, ηext (deduced from integrated photoluminescence measurements), is a sensitive measure of the non-radiative recombination rate 1−η provided that other, parasitic, absorption losses are small. Our highest measured value ηext = 72%, which to our knowledge is by far the highest for spontaneous emission ever measured for GaAs, is explained by an average number of 25 photon regeneration processes with η = 99.7% efficiency.
Design of optoelectronic implementation of biological vision models
Authors: Guest Clark C.
Published: February 2023

Human vision employs principles that differ significantly from existing technological pattern recognition systems. Yet, based on existing models, the biological process may be broken down into a series of steps that map well onto parallel optoelectronic implementations. In particular, the Grossberg-Mingolla boundary contour systems (BCS) model of vision will be examined here. The principal feature of the BCS system is its ability to complete boundaries between image regions that differ in luminance or textural distribution. This model will be explained and then interpreted in terms of cascaded stages of correlation that may be implemented optically. Verification of this interpretation will be provided through simulations of its performance on complex scenes. Translation of the biological model to a correlator model raises a number of engineering issues. These will be addressed, and their resolution will be explained.
Microlasers
Authors: Slusher Robert E.
Published: February 2023

Optical microresonators are of interest for studies of quantum electrodynamic (QED) phenomena as well as for low threshold microlasers and efficient LEDs. As the optical mode volume of a microresonator approaches a cubic wavelength, the number of modes interacting with the optically active spectral region in the microresonator approaches unity. This tutorial will begin with a description of QED phenomena in thin films, optical resonators, and local optical modes in photonic band gaps. Both spontaneous radiation patterns and rates are strongly modified in microresonators. Next several experimental systems will be reviewed, including distributed Bragg mirrors for vertical emitting semiconductor microresonators, whispering-gallery modes in spheres and disks, and localized optical modes in periodic dielectric structures. The behavior of microlasers near the lasing threshold will be discussed, including the light output as a function pump power and the expected spectral linewidth. A number of interesting applications for microlasers and microresonators, including efficient LEDs, microlaser arrays, optical interconnects, squeezed light sources, and high functionality microphotonic circuits, will be described.
Binary birefringent micropatterns defined in polymers
Authors: Shi Yongqiang , Steier William H. , Chen Mai , Dalton Larry R.
Published: February 2023

Polymers with disperse red 19 (DR19) pendant groups showed a large photoinduced birefringence when exposed to linearly polarized ultraviolet or short wavelength visible light because of trans–cis isomerization of DR19 groups. High resolution birefringent micropatterning (>2000 lines/mm) has been demonstrated by using this entirely dry processing technique. We have defined binary wave-plate arrays of 5 × 5 μm pixel size with different optical axes and phase delays in alternating pixels by using a commercial mask aligner. This photo exposure method is simple and versatile. The optical axis of the wave plate is defined in the direction of the exposure polarization so that wave plates with different orientations can be defined in the same film by proper masking and control of exposure polarization. The phase delay is controlled by the exposure fluence; therefore, different retardations can be obtained from different exposure doses. These multi-orientation birefringent arrays can find applications in areas of binary diffractive optics, optical information processing, storage, and display. Some examples are shown experimentally. Birefringent optical waveguides have also been defined by this technique. Their properties and potential device applications will be discussed.