bluuebunny/crossref_metadata_2025 huggingface dataset:
Colored matched spatial filters recorded in LiNbO3
Authors: Mayers A. W. , Yu F. T. S. , Rajan S. , Wu S. , Gregory D. A.
Published: February 2023

In many applications it is desirable to implement a correlation system capable of performing color pattern recognition. With mixed gas lasers such as the argon–krypton laser, it is possible to have a single source produce a collinear beam composed of red, green, and blue wavelengths. In this paper we investigate recording reflection and transmission matched spatial filters in photorefractive LiNbO3. We limit our discussion to simultaneous recording of the filter as opposed to sequential recording. We show that the reflection filter suffers from low diffraction efficiency as a result of grating competition, while the transmission filter suffers from wavelength crosstalk caused by grating beating. Finally, we demonstrate a transmission filter that uses a grating in the input plane to separate the wavelengths in the filter plane, and eliminate the color crosstalk.
Optical disk-based tandem joint transform correlator
Authors: Hsu Fu Kuo , Yu Francis T. S. , Yin Shizhuo , Nishihara Eiichiro , Nishikawa Takashi
Published: February 2023

In previous configurations of the optical disk-based joint transform correlator (ODJTC),1,2 the light waves emerging from the input and reference images each travel through a different arm of a Mach-Zehnder interferometer. In a tandem joint transform correlator, the input and reference images share the common optical path. The input and reference planes are conjugate to match the quadratic phase factor. The magnification ratio of the two image planes is selected to match the scale ratio of the two functions. This common path configuration has a number of advantages, such as stability, high optical performance, simplicity, and versatility. There are three spatial light modulators (SLMs) incorporated in the ODJTC. The optical disk (OD) is used for the reference image. One liquid crystal television monitor (LCTV) for the input image, and another LCTV for the joint Fourier transform hologram. The OD-stored images can be either transmission or reflection type. The scanning of the OD-stored image can be achieved by translation of either the optical axis or the OD radially.
Joint transform correlation peak sharpening using intensity compensation filtering
Authors: Yu Francis T. S. , Cheng Feng , Hsu Fukuo , Gregory Don A.
Published: February 2023

The intensity compensation filtering (ICF) peak-sharpening process for a hybrid joint transform correlator (JTC) can be divided into three steps. First, the power spectrum of the reference is taken in by a CCD camera and stored in the computer. The filter function is then obtained from the thresholded inverse of the power spectrum. Second, the object is turned on and the joint Fourier power spectrum is again picked up by the CCD camera and sent to the computer. In the last step, or the readout, the computer displays the filter function and the joint power spectrum on two overlapping SLMs that are illuminated by a coherent readout beam. The correlation peak is detected at the output plane. In some situations, the two SLMs can be combined into one and the multiplication of filter function and joint spectrum is performed by computer, especially if the filter is binarized or ternarized, or when the computer multiplication is swift enough to meet the real-time requirements.
Pattern recognition by photon echoes
Authors: Talagala P. , Kim M. K.
Published: February 2023

We demonstrate, we believe for the first time, the capability of spatial pattern recognition by backward stimulated photon echo (BSPE) in a low temperature solid activated by rare earth ions. The BSPE experiment is done with three time-delayed input laser pulses. The first pulse (DATA) contains several characters in its beam profile, the second pulse (WRITE) is a plane wave, and the third (READ) has the search character. The echo pulse profile has peak intensity at the position of the search character. The experiment has a time scale of several tens of nanoseconds. Pattern recognition by BSPE is a result of the convolution/correlation property of holographic four-wave mixing geometry. In contrast to the photorefractive processes, however, the BSPE in rare earth-doped solids is a resonant coherent optical transient effect. By combining spatial and temporal holographic processes of BSPE, it would be possible to construct a high density, high speed optical processor of spatial and temporal data using BSPE.
Contrast nonlinearities and the stimulus selectivity of cortical neurons
Authors: Albrecht Duane G.
Published: February 2023

The contrast response functions of cat and monkey visual cortex neurons reveal two important nonlinearities (expansive exponents and contrast gain control) that can have beneficial effects on stimulus selectivity. As contrast increases, response generally increases rapidly with a power function exponent greater than 1.0 (the average is 2.5), and then saturates; further, when measured at different spatial frequencies, the contrast response functions shift vertically (on log–log coordinates) indicating a contrast-set gain mechanism.1
Inverse scattering transform of transient nonlinear optical phase conjugation
Authors: Ghosh Roy D. N. , Rao D. V. G. L. N.
Published: February 2023

Transient NOPC is analyzed from the viewpoint of potential scattering. The probe, the nonlinear optical medium, and the conjugate fields are represented by appropriate wavepackets. Instead of considering the generation of a conjugate wave as a coherent sum of the diffracted fields from the gratings, the point of view here is that of resonant collision of a probe field wavepacket with that of the material medium. The coupling is provided by third-order nonlinear optical susceptibility. Transient NOPC is considered here as a three-wave resonant interaction process in which the middle envelope of the material medium is not significantly changed during the interaction as is usual in NOPC using four-wave mixing (FWM). The coupled probe-conjugate field equations are solved as a Zakharov-Shabat eigenvalue problem in the nonoverlapping wavepacket configuration and a general expression for the conjugate field at the FWM cell exit is obtained, which is then specialized for a constant coupling of finite extension. Finally, the inverse scattering transform methodology is used to investigate the time asymptotic behavior of the conjugate signal at the cell exit as well as the time evolution of the potential, which has received considerable attention lately.
Near threshold dynamics of multimode class B laser model
Authors: Adkison D. , Hodges S. E. , Olsen T. , Raymer M. G.
Published: February 2023

Near-threshold multimode laser dynamic are being studied to gain some insight into their noise characteristics. Previous studies of a class A dye laser system1 showed that observed fluctuations were dominated by coherent, deterministic effects. Simple scaling arguments, based on this model, suggest that shortening the laser cavity should increase the relative importance of quantum fluctuations. Our study focuses on class B lasers (e.g., short-cavity dye and Ti:sapphire lasers), in which the cavity loss rate is of the same order as the spontaneous emission rate. Semiclassical equations are derived using Bloch and wave equations. For this system we may adiabatically eliminate the polarization but must retain both the electric field and inversion as dynamic variables. The inversion is then doubly expanded into both temporal and spatial modes. The high-frequency inversion modes are adiabatically eliminated. Finally, a Langevin noise term is added to the electric field-mode and inversion equations. An analysis of the turn-on dynamics of the laser is performed and compared to experimental results from our laboratory and to earlier analytical predictions.2
High-speed wide band board-to-board optical interconnection
Authors: Sun Zonojian , Lu Huey , Chen Ray T. , Jannson Tomasz
Published: February 2023

Increases in modulation speed and interconnection distance have driven electrical interconnects to their theoretical limits, beyond which optical interconnections are the only possible alternative. In this paper, we report, we believe for the first time, a 14-GHz board-to-board optical interconnection. The optical data bus boards were constructed by depositing a graded-index (GRIN) polymer film on tope of a substrate. Thanks to the GRIN characteristic of the polymer film, an array of high-index substrates can be employed as the optical data bus boards. The propagation loss of the optical data bus was measured by the two prism method. We routinely achieved ~0.5 dB/cm propagation loss on various substrates. Board to board optical interconnection was achieved using a microprism array as small as 100 µm with a coupling bandwidth larger than 800 nm, which is two orders of magnitude larger than the 3-D optical interconnects based on holographic optical elements. A 1-GHz baseband signal was provided using an external modulator. Finally, the high-speed signal was detected by integrating a photodetector at the end face of the output microprism.
Dynamics and interaction of optical vortices in lasers
Authors: Oppo G.-L. , Alessandro G. EX , Kent A. , San Martin J. , Firth W. J. , Gil L.
Published: February 2023

We analyze the complete set of partial differential equations describing the dynamics of a ring cavity laser with spherical mirrors and 2-D transverse dependence of both the field and the pump. Several optical vortices can arrange themselves in crystallized structures that rotate around the laser beam center. These solutions are temporally and spatially stable to perturbations. The mechanism of interaction between the rotating vortices is analyzed. In particular we find that the asymptotic position of the vortices is at the balancing of the repulsive force among vortices of the same charge and the drift force caused by the spatial dependence of the parameters of the equations. Such a force tends to confine the vortices at the center of the beam. Relevance of these new solutions to the onset of chaotic and, more generally, of defect mediated turbulence is discussed. The effects of transverse boundary conditions as well as signal injection on the nature and stability of the optical vortices are also studied.
Amplification and TEM00 continuum generation of femtosecond pulses
Authors: Hayden Carl C. , Kimmel Mark W. , Trebino Rick
Published: February 2023

We have built an apparatus capable of generating tunable 60-fsec, 350-μJ, TEM00 pulses in the visible and near IR. It involves a colliding-pulse mode-locked dye laser stably producing pulses as short as 35 fsec, a novel bowtielike combination preamp/amplifier, pulse compressor, solid-state TEM00 continuum generator, and two-stage Bethune-cell amplifier. Here, we describe in more detail the novel aspects of our apparatus (the bowtie preamp/amplifier and the continuum generator), which represent useful advances over current technology. Pumped by a short 5-nsec pulse from a frequency-doubled Nd:YAG laser, the bowtie amplifier allows only three passes by the fsec pulse through the dye cell during the pump-pulse duration. However, additional amplification, using a larger spot size, is desirable. Because pumping is longitudinal, the dye concentration of a second amplifier into a single six-pass cell in which two separate spots are pumped. We measure a gain of 2 × 105 with this device and output pulses of 100 μJ (and 50 fsec after compression) using a pump power of 25 mJ. Our continuum generation apparatus involves a spatial prefilter, variable energy attenuator, and careful focusing to a spot just prior to the 1/16 in. thick quartz plate continuum sample. The energy of the input pulse is limited to avoid small-scale self-focusing, and the input beam angular dispersion is carefully limited to avoid significantly greater angular dispersion in the continuum output. In this way, we obtain approximately 10 nJ of light in a 20-nm bandwidth 2500 cm-1 away from the input wavelength. While this represents a fairly low efficiency, it is easily amplified to high power due to its good spatial quality.
Nanosecond transmission to total internal reflection switching/limiting via laser-induced cavitation in carbon suspensions
Authors: Lawson C. M. , Michael R. R. , Euliss G. W.
Published: February 2023

We have experimentally demonstrated nanosecond transmission to total internal reflection (TIR) switching and optical limiting resulting from laser induced cavitation in films of carbon microparticles suspended in ethanol. The films are bounded by two glass windows separated by mylar spacers. Laser-induced cavitation occurs when the fraction of the incident energy absorbed by a carbon particle is sufficient to heat up and vaporize a small volume of the surrounding liquid. These small vapor bubbles coalesce to form larger vapor bubbles. Total internal reflection switching/limiting occurs at the glass-vapor interface that is formed when these bubbles meet the glass substrate. Nonlinear refractive-index changes as large as 0.3 have been obtained using a single 5-ns Q-switched doubled (532-nm) Nd:YAG laser pulse. Switching and limiting thresholds as low as 0.2 J/cm2 have been measured. More than 90% of the incident energy has been reflected using the cavitation/TIR switching mechanism. The observed limiting results from two mechanisms: energy removal via TIR and scattering from microplasmas that form when the carbon particles are thermally ionized by the incident laser energy. We have investigated the effects that particle concentration, film thick ness and film bias temperature have on the cavitation/TIR process and limiting behavior.
Real-time double-exposure interferometries using a self-pumped conjugator with Cu:KNSBN crystal
Authors: Zhang Jingwen , Xu Haiying , Pu Hongbin , Yuan Yang , Xu Kebin , Jiang Quanzhong
Published: February 2023

We describe real-time double-exposure interferometies with an internally self-pumped conjugator employed by a photorefractive crystal Cu:KNSBN. The device offers many advantages as a nondestructive testing device: elimination of the effects of turbulence or optical distortion, self-alignment, high reflectivity, and so on. In our experiment, an argon ion laser beam at 0.515 μm is expanded and collimated to a 4-cm diameter beam size. The collimated beam passes through a transparent test object and is focused into a photorefractive crystal Cu:KNSBN with 51% phase-conjugate reflectivity. A beam splitter separates the conjugate beam generated by the self-pumped conjugator, and a CCD camera receives the output interfering fringes formed in double exposure. In the first exposure, the image of the test object is conjugated by the self-pumped conjugator. Applying force to the test object, an internal shape change occurs. The image that its phase has changed is written in the crystal again. Th-en the interfering fringes are received by the CCD camera and are analyzed by a computer. Using this device, the defects of the test object can be inspected in real-time.
Real-time corrected long baseline interferometer system
Authors: Vernon Russell G.
Published: February 2023

A design concept and analysis for a long interferometer imaging system that uses realtime higher wavefront control, tilt and piston control has been developed to: (1) stabilize the fringe field associated with the mutual coherence function, (2) measure visibility amplitude and closure phase, and (3) allow the investigation of celestial sources at lease down to 15th magnitude. Pupil plane piston phase control and closure phase measurement is accomplished on three 1-m apertures simultaneously by differential phase modulation and Fourier decomposition. Atmospheric wavefront sensing is accomplished in all three telescopes using Rayleigh scattered 15-W laser guide stars focused at 20 km. Tilt sensing and correction is accomplished using the imaged source field. Analysis is performed on the wavefront control assembly to tradeoff laser guide star power requirements, optical train efficiency, wavefront sensor measuring accuracy, number of wavefront sensor subapertures, deformable mirror actuators and servo bandwidth requirements. Analysis is performed on the tilt stabilization system to tradeoff source field irradiance requirements, optical train efficiency, track sensor accuracy and servo bandwidth. Analysis is performed on the piston control sub-system to optimize the measurement of closure phase and visibility amplitude over a narrow spectral bandwidth, to tradeoff source field irradiance requirements, piston measuring accuracy, and visibility amplitude accuracy.
Interferometric radius of curvature measurement
Authors: Cochran Eugene R.
Published: February 2023

The current state-of-the-art for measuring the radius of curvature involves an interferometer, a slide rail, and a distance measuring interferometer or digital radius slide. Using these components it is possible to implement a noncontact spherometer. This technique involves positioning the optic under test at two positions: cat’s eye and confocal. First, the optic is placed so that the transmission sphere is focused on the surface of the part, the cat’s eye position. At the cat’s eye position, the distance is recorded using the distance measuring interferometer. Also, an interferometric measurement is made that will indicate the precision in determining the position of the element relative to the focus point of the transmission sphere. Next, the test optic is moved so that the focus of the transmission sphere is at the center of curvature, the confocal position. At the confocal position, the distance is recorded using the distance measuring interferometer once again. A measurement is acquired at this position that provides a sensitive indicator of where the radius of curvature coincides with the focus of the transmission sphere as well as information about the surface figure and irregularity. Once the optic is tested in both cat’s eye and confocal positions, the distance between the two positions may be calculated. Furthermore, nulling errors or the deviation of the test optic from its best focus at each position may be calculated by using the interferometer data. The sources of error using this technique include unmeasured or erroneous measured motion, alignment errors, nulling errors, and environmentally induced positional drift. However, since the wavefront at each position is known and the axial focus error at each position is calculated, knowledge of the numerical aperture at each position allows computation of a corresponding nulling error. This compensates for the error incurred by not precisely positioning the surface at the cat’s eye or confocal position. Using these techniques, measurement to a few parts per million can easily be made.
High-resolution distance meter using optical waveguide modulators
Authors: Matsumoto Hirokazu , Saitou Michiaki , Fujima Ichiro , O'ishi Tadanao
Published: February 2023

Recently, high-resolution distance measurement of pm order in the range of 1-100 m is required to evaluate large-scale constructions. We have developed an optical time-of-flight distance meter, using two waveguide-type modulators and a laser diode of a wavelength 1.3 pm. In this system, the laser beam is interferometrically modulated at 3.5-GHz frequency and demodulated at (3.5 GHz + 50 kHz). The light reflected by the target is detected with a good SNR, >40 dB. This system is evaluated at distances up to 250 m, using a 50-m traveling carriage and an interferometric fringe counting system. From the results, the linearity in phase measurement was ~5 μm in standard deviation, after compensating the systematic cyclic error from the reflection on the surfaces of optical fibers and a phase sensitive phase meter.
Confessions of a video warrior
Authors: Rogers Steven K.
Published: February 2023

This talk will present results from recent experiences with technical videos at the Air Force Institute of Technology. From the perspective of a technical person trying to accomplish information transfer several failures and successes are reviewed. The video examples shown will include technical video proceedings, technical tutorials, laboratory commercials, and research summaries for a nontechnical audience.
Encoding of holograms by annealing in combination with other iterative algorithms
Authors: Peter T. , Lupken H. , Wyrowski F. , Bryngdahl O.
Published: February 2023

Simulated annealing is a powerful method to numerically treat nonlinear optimization problems. The algorithm is advantageous in respect to flexibility and independence of start conditions. However, a drawback is its slow rate of convergence compared to projection procedures.
Nonlocal cancellation of dispersion
Authors: Franson J. D.
Published: February 2023

Two classical, coincident light pulses propagating through two different dispersive media will become broadened and their degree of coincidence will be reduced. The width of the coincidence curve can be shown to be proportional to

(

β
1
2

+

β
2
2

)

x
2

, where β1, and β2 are the dispersion coefficients in the two media and x is the distance traveled. When entangled photon pairs from parametric down conversion are considered instead, it is found that the width of the coincidence curve is then proportional to (β1 + β2)2x2, which gives an interference term of 2β1β1. If β1 = β2, the dispersion experienced by one photon can exactly cancel the dispersion experienced by the other in such a way that their coincidence is maintained.
Proposed test of Bell’s inequalities with atoms
Authors: Fry Edward S. , Li Shifang
Published: February 2023

It is well known that Bell’s inequality may be violated for special quantum states, e.g., an entangled state for a pair of particles. The entangled state is generalized here into a polyentangled state. Specifically, instead of only two possible states for each individual particle of the pair, several states are possible in an entangled way. An experimental realization for the polyentangled state is presented. It is the state for a pair of atoms in their Zeeman sublevels, in which the atoms are produced from dissociation of a homonuclear (I = 1/2) paradimer that is initially in a J = even rotational state of the singlet electron state. The three possible angular momentum components (M2 = 0,±1) in a specific direction can be determined because the different Zeeman sublevels can be selectively excited by polarized lasers, and then subsequently detected by photoionization. Because of the high detection efficiency (>90%) and fast responsivity (<10 ns) for these processes, the two main loopholes in previous LHV experiments using optical photons can be blocked.
Effect of the volume scattering function on the errors induced in radiance calculations by using scalar rather than Stokes vector theory in an atmosphere–ocean system
Authors: Adams Charles N. , Kattawar George W.
Published: February 2023

Virtually all radiative transfer calculations in the ocean have neglected polarization, automatically leading to errors in the radiance distribution. This implies that if one knew the inherent optical properties exactly and used an exact scalar theory to calculate the apparent optical properties, the calculations would not agree with measurements. A Monte Carlo program has been written and tested that will simultaneously calculate radiances, neglecting polarization effects, and also the complete Stokes vector at any altitude or depth in an inhomogeneous atmosphere-ocean system. The program can also handle a stochastic dielectric interface with fixed index of refraction where a wind speed can be specified; however, for the results presented here, we assume a flat ocean. Comparisons are given to show the errors that are encountered when one neglects polarization effects for different types of volume scattering function assumed for the ocean. These errors are shown to be function of solar zenith angle, detector location, single scattering albedo, and shape of the volume scattering function in the ocean. We have assumed Rayleigh scattering only for the atmosphere to simplify interpretation.
Thin PLZT film Fabry-Perot light modulators
Authors: Krishnakumar S. , Ozguz V. , Fan C. , Esener S. , Lee S. H.
Published: February 2023

One of the techniques used to make smart spatial light modulators (S-SLM) involves the deposition of a thin film of electrooptic lead lanthanum zirconate titanate (PLZT) on silicon-on-sapphire substrate next to silicon circuits. By fabricating silicon devices prior to deposition of PLZT films, VLSI circuits of any complexity can be achieved and linked to PLZT modulators on the same sub-strate. The amount of light modulation that can be achieved through thin PLZT fdms can be dramatically improved by placing the film in a Fabry-Perot interferometer. The interferometer would also offer attractive features such as high speeds (due to low intrinsic capacitance) and low switching energies. The first step in the development of Fabry-Perot interferometers involves the deposition of PLZT films on a reflective layer such as highly oriented thin platinum films grown on silicon or sapphire substrates. A final step in the process would be the deposition of a top layer of a mirror stack.
Time–frequency processing of high-range resolution radar returns
Authors: Sabet-Peyman F. , Cohoon R. L. , Finnigan J. S.
Published: February 2023

The properties of the returned signals associated with high range resolution (HRR) radars are influenced by Doppler and constantly vary according to the target aspect relative to the radar line of sight. To effectively sort and classify the returned signals the spectral and temporal contents must be measured simultaneously. A 2-D processor implementing the Wigner transform of the received signals is designed and demonstrated. This architecture is based on acoustooptics and provides the time–frequency information related to the scattered chirped signals in real time at the output plane. In this architecture the returned signals modulate the laser beam via a Bragg cell. A cylindrical lens of appropriate focal length is used to dechirp the returned signals and a second Bragg cell to generate the time base, followed by Fourier transform optics. In this paper we discuss the architecture, its performance, and present the results of recent experiments. System performance is discussed in terms of unintentional signal variation, the dechirping lens and Bragg cell aperture and bandwidth.
Upconversion lasers: the vista from mestastable levels
Authors: Krupke William F.
Published: February 2023

Recent advances in high power semiconductor laser diode arrays has revived interest in the development of practical upconversion lasers (efficient, power/energy scalable, room temperature operation, etc.). Upconversion lasing in several bulk crystals1 and glass fibers2 doped with various rare earth ions, have been reported. To date, diode-pumpable bulk crystal upconversion lasers have only operated inefficiently at cryogenic temperatures, whereas room temperature fiber upconversion lasers with interesting efficiencies have recently been reported.2,3
Geometrical approach of the circular harmonic filters
Authors: Sheng Yunlong , Premont Guy , Leclerc Luc , Arsenault Henri H.
Published: February 2023

A circular-harmonic (CH) filter contains only one component of the object that gives rotation in variance. But an infinity of objects could have the same center correlation value although most of those are not realistic objects. On the other hand, a CH filter performs the CH expansion of the input about every point in the plane (r,θ). The correlation output can be expressed as where F
m
(p) and G
m
(p) are the CH functions of the filter and of the input in the Fourier plane respectively, Jm(2πpr) is the Bessel function. This equation shows clearly that apart from the center r = 0 θ = 0, the 2-D correlation of a CH filter of order m depends on the CH components of all the orders and is then unique of a given input. The center output intensity depends only on the order m. But the position of the output peak depends on all the orders.
Contrast contrast determines perceived contrast
Authors: Chubb Charles , Solomon Joshua A. , Sperling George
Published: February 2023

A testpatch of visual texture has greater apparent contrast when it is surrounded by a uniform mean gray field than by a background of similar, high contrast texture. Temporally modulating the contrast of surrounding texture induces a substantial antiphase modulation of testpatch apparent contrast. Using a nulling procedure, we have found that this induced modulation of testpatch apparent contrast is (1) strictly monocular: there is no induced modulation of apparent contrast when the testpatch and surround are presented to opposite eyes; (2) spatial frequency specific: when testpatch and surround textures are filtered into nonoverlapping octave-wide spatial frequency bands, the modulation of surround contrast has little effect on testpatch apparent contrast; (3) orientation specific: when the testpatch and surround textures are of opposite orientation, the magnitude of induced contrast modulation may be much less than when they are of the same orientation.
Contrast gain control and spatial frequency adaptation
Authors: Wilson Hugh R. , Humanski Richard A.
Published: February 2023

Spatial frequency adaptation was first believed to result from some form of neuronal fatigue. To test this we have reexamined the effects of spatial frequency adaptation on the contrast increment threshold function. Using 3.0 cpd adaptation and test stimuli, we have found that the power law exponent of the increment threshold function decreases from 0.62 before adaptation to 0.39 following spatial frequency adaptation. A re-analysis of data by Greenlee and Heitger1 shows a similar decrease in the exponent. In a second experiment we examined the effect of test stimulus presentation time on spatial frequency adaptation. As expected, we found that thresholds were elevated by an average factor of 2.2 when test stimuli were presented for 500 msec. However, when a 30-msec presentation was used, the threshold elevation was reduced to only 1.2, just slightly above the pre-adapted threshold.
Overview of laser diode electrooptical characteristics
Authors: Johnson Lawrence A.
Published: February 2023

Today over 98% of all lasers sold in the world are semiconductor laser diodes. With applications multiplying daily, these devices promise to do for optics what the transistor did for electronics. In order to successfully apply laser diodes, a good understanding of their operating characteristics is essential.
Long distance soliton transmission systems
Authors: Smith K.
Published: February 2023

Ultralong distance transmission employing optical solitons and periodic lumped amplification offers great promise for future highbit rate communication systems. To exploit the maximum potential of such systems, it is important to ad dress the issues of optimum source and amplifier configurations. It may be desirable to employ sources that generate fundamental solitons directly. One such laser source—the erbium fiber soliton laser—is described. We discuss the average soliton dynamics of the laser and the use of this model in soliton transmission systems. We also describe experiments designed to explore alternative amplifier configurations. Since the transmission capacity of the system is ultimately limited by the accumulated effects of amplified spontaneous emission, the combination of a fiber amplifier with the noise-eating properties non-linear fiber loop mirror may be extremely attractive. We also describe experiments underway relating to soliton transmission in recirculating fiber loops. Various configurations are described including novel loop mirror/amplifier architectures for ultrahigh bitrate soliton switching, transmission, and optical memory applications.
Impact of optical amplifiers on lightwave communications
Authors: Tkach R. W.
Published: February 2023

The advent of erbium-doped fiber amplifiers has made economical low-noise, and wide-band optical amplification in the low loss 1.5-p.m wavelength region a reality. This fact is causing a revolution in thinking about lightwave communication systems. The longest optical spans in commercial use today are <100 km, but, using these amplifiers, systems spanning the oceans without electronic regeneration are under development. Perhaps even more revolutionary will be the impact of these amplifiers on terrestrial long-haul and short distance communications. New systems architectures, which were impossible with electronic regeneration, can now be considered. Multiple channels at different wavelengths can be used, since the channels need only be separated at the ends of the system, compared to demultiplexing and regenerating every 40 km in a conventional system. In networks, the loss of components used for optical switching and signal routing can be compensated with amplifiers. We can anticipate a large increase in the available capacity and sophistication of optical communications. An important challenge lies in discovering new ways of using this resource.
Effect of optical fiber birefringence on long-distance soliton transmission
Authors: Menyuk C. R.
Published: February 2023

It is often stated that soliton propagation in optical fibers is modeled mathematically by the nonlinear Schrodinger equation which has soliton solutions. However, real fibers contain many nonidealities that lead to changes in the mathematical models that must be used to study them. These effects include nonconservative phenomena such as attenuation which must be compensated or Raman, Brillouin, and Rayleigh scattering which must be made negligible. These effects also include conservative phenomena such as higher-order dispersion and birefringence. These effects are benign and can typically be ignored. The reasons why conservative effects are benign can be understood by an analogy to simple nonlinear springs. The equations that model birefringent optical fibers are described, and self-trapping is demonstrated. Finally, a model of randomly varying birefringence is obtained. It is shown that, at lowest order in an appropriate perturbation expansion, the usual nonlinear Schrodinger equation results, while at higher order there is a slight depolarization.
Intrapulse-Raman-scattering soliton timing jitter in ultralong distance transmission
Authors: Moores John D. , Haus Hermann A.
Published: February 2023

Spontaneous emission from amplifiers perturbs the amplitudes and widths of solitons in ultralong distance transmission. These perturbations alter the rate of self-frequency shift (intrapulse Raman scattering) of the solitons, in turn changing the rate of inverse group velocity shift per unit distance, through group velocity dispersion. This results in a spread in the arrival times at the receiver. Although these deceleration shifts are weak for pulses >1 ps wide, they can be significant when integrated (twice) over ultralong distances. We find, for reasonable parameter values, that the timing jitter from this effect, and thus the propagation distance limit, exceeds that of the Gordon-Haus limit1 at bit rates as low as a few tens of Gbit/s. Such bit rates might be achievable if all-optical pulse restoration elements2 are introduced into long distance communications systems. With such elements, the distance limitations imposed by timing jitter no longer apply to the entire system length but rather to the distance between pulse restoration elements, and this increases the achievable bit rate-system length product.
Instrumentation integration in large systems: the OMEGA laser upgrade at the University of Rochester as an example
Authors: Kelly John H.
Published: February 2023

The University of Rochester’s Laboratory for Laser Energetics is upgrading its existing 24-beam, 2.5-kJ UV OMEGA laser to a 60-beam, 30-kJ UV laser. In order to successfully operate a system of this complexity and size, a variety of optical diagnostics for beam pointing, centering, energy, temporal pulseshape, gain, and loss, in both the infrared and ultraviolet, must be deployed. These diagnostics must ensure near-identical performance of each of the 60 individual beamlines. In addition to its own performance requirements, each diagnostic always faces stringent cost limitations and almost always a space limitation. This presentation describes the OMEGA laser upgrade and some of the novel concepts used in its design. Examples of several of the diagnostics are traced through their conceptual and prototype development to illustrate the trade-offs made in their design. Often the trade-offs were made between diagnosing potential problems or reducing their probability to acceptable levels. Significant cost savings were made by combining optical trains used for several diagnostics or with some other component of the laser system. In some cases one or a few diagnostics were multiplexed over the 60 beamlines. In yet other cases no compromise could be made and individual instruments were deployed for each of the beamlines. The entire process has so far proved to be highly interactive with instrumentation requirements and laser requirements often changing to accommodate advances, new understanding, and/or economies. This interaction was formalized by the establishment of a systems engineering group and a requirements review board.
Generation of gap solitons
Authors: de Sterke Martijn
Published: February 2023

Gap solitons can occur in nonlinear periodic stacks. They would, in general, be created using a powerful external light pulse. In doing so it is important that the external energy required be minimized. It is shown that, among other things, the refractive indices of the stack and of the surrounding media play a crucial role in determining the efficiency. Particularly important also are the parameters of the outer layers of the nonlinear stack.
Temperature and concentration measurements of NO gas by folded BOXCARS
Authors: Zhao Shuo-Yan , Shao Yan , Zhang Pei-Lin
Published: February 2023

Experimental CARS spectra of the Q-branch (v = 0-v = 1) of NO gas at different temperatures (300–1400 K) has been performed with a folded BOXCARS technique that can provide high spatial resolution for diagnostic purposes. A theoretical calculation taking into account the laser linewidth and lineshape is presented. By comparing the theoretical spectra with the experimental ones, the point temperatures measured by the CARS method are determined. The measurement accuracy of the method is discussed. CARS measurements have also been performed for various NO gas pressure (0.04–1 atm) in order to study the pressure dependence of the CARS spectral shape. A concentration measurement method using the intensity of virbration–rotational line is discussed. It is found that the concentration dependence of line intensity is in agreement with the theoretical result for high J values.
Remote laser diagnostics of acoustically levitated drops
Authors: Biswas A. , Leung E. W. , Trinh E. H.
Published: February 2023

Ground based experiments on acoustically levitated samples are being conducted in an effort to simulate containerless materials processing in the microgravity environment of space. Remote laser based diagnostic techniques are being investigated for real-time monitoring of drop stability and fluid dynamics as well as physical parameters related to materials processing. We present results of elastic light scattering used for monitoring and studying the rotational dynamics and evaporation behavior of levitated transparent millimeter-sized drops.
Investigation of electromagnetic fields with sub-wavelength resolution by scanning near-field optical microscopy
Authors: Butler D. J. , Roberts A. , Nugent K. A.
Published: February 2023

At the University of Melbourne we are developing a program of research into near-field scanning optical microscopy (SNOM). The principle aim of this program is to characterize the optical properties of the near-field probe commonly used in such microscopy. To do this we are using near-field probes to perform detailed measurements of well characterized diffracted optical fields. Such structures include near-field diffraction patterns of straight edges and high N. A. lens focal distributions. Many of the fields have not previously been directly observed and, in some cases, are of theoretical and/or technological interest. In the first steps toward achieving our aim, intensity maps in planes parallel, and perpendicular to, the axis of a single-mode optical fiber have been recorded. Previous investigation of these fields has only been possible in the near-field using an analogue microwave experiment. The maps were recorded by scanning a 100-nm diameter aperture of the type used in SNOM through the fiber output, and they contain both near-field and far-field information. The techniques yielded data with a dynamic range of better than 103. The results are compared with theoretical predictions.
Broadband optical voltage and electric field sensor based on ferroelectric thin films
Authors: Chen J. , Yin S. , Cross L. E.
Published: February 2023

Lanthanum-doped lead titanate (PLZT) and lead magnesium niobate-lead titante (PMN-PT) thin film waveguides were prepared by chemical processing methods (solgel, MOD). Electrooptical effects of thin films have been investigated by using a prism out-coupling technique. The modulation sensitivity of conventional optical voltage and electric field sensors has a narrow detecting frequency band because piezoelectric effects of materials occurs at the low frequency region. New optical voltage and electric field sensors have been developed which have a constant modulation sensitivity up to high frequency components by using PLZT and PMN-PT thin films. The electrostrictive effect on optical modulation of ferroelectric thin films has been discussed also.
Laser-excited amplified spontaneous emission of atomic hydrogen in low pressure flames
Authors: Heard Dwayne E. , Jeffries Jay B.
Published: February 2023

Amplified spontaneous emission (ASE) has been observed at the Balmer α wavelength from two-photon excited 3S and 3D hydrogen atoms. ASE has several advantages for atom diagnostic measurements in reacting flows compared to resonance enhanced multiphoton ionization or laser-induced fluorescence (LIF). The ASE signal is collimated along the excitation laser beam, which simplifies optical alignment, reduces the necessary optical access, and increases the spectral brightness. These can be significant advantages in reacting flows and material processing plasmas where ion collection probes can alter the process and LIF measurement precision and detectivity is often limited by background optical emission. Simultaneous ASE and LIF measurements in a variety of collisional environments are discussed, which demonstrate the influence of gas collisions on the ASE signal. Bandwidth measurements of the ASE are demonstrated for single laser pulses.
Diode laser injection seeding of a pulsed Ti:sapphire laser for remote sensing
Authors: Wang L. G. , Barnes J. C. , Edwards C. , Hess R. V. , Ponsardin P. , Sachse G.
Published: February 2023

High pulse energy (100–150 mJ) high spectral purity (>99.7%) injection seeding is reported for a pulsed unstable resonator Ti:sapphire laser using a cw single-mode 100-mW diode laser in the 820-nm region. The laser characteristics meet the strict requirements of a NASA Lidar Atmospheric Sensing Experiment mission in differential absorption lidar (DIAL) remote sensing of water vapor. Long and short term laser frequency stability is obtained by locking the diode laser frequency to an absorption line of water vapor in a reference cell using a frequency modulation technique. Operation on and off the water vapor absorption lines for the DIAL measurements is achieved by applying current pulses to the diode laser, which greatly simplifies the DIAL system. The spectral purity of laser output is measured using two White cells with a total path length of 400 m. Diode laser side mode seeding was found to be the major limitation to higher spectral purity. By suppressing the diode laser side mode with a solid etalon, spectral purity higher than 99.7% has been obtained.
Tunable diode laser sensor for temperature and velocity measurements of oxygen
Authors: Philippe Louis C. , Hanson Ronald K.
Published: February 2023

Tunable semiconductor lasers are attractive sources for measuring molecular species’ absorption lineshapes in flowfields. Their wide modulation bandwidth allows fast time response suitable for studying transient flows. For a weak absorption such as the oxygen A-band near 760 nm, laser intensity modulation which limits measurement sensitivity can be eliminated by combining laser wavelength modulation and second-harmonic detection. This technique is used in the measurement of velocity and temperature of oxygen in transient high temperature and high speed flows generated in a shock tub. A 3-mW GaAlAs laser diode is used to monitor oxygen absorption lineshapes at a 10-kHz rate in the end section of a shock tube along two optical paths with a 30° relative angle. Laser wavelength markers are obtained by passing a third beam through a low finesse etalon. The small amplitude 10-MHz modulation is directly coupled to the laser, and second-harmonic signals are demodulated by frequency mixers in a 500-kHz bandwidth. The oxygen velocity behind the incident shock is derived from the Doppler shift between the lines recorded along the two beam directions. Typical absorptions in the range 0.2–1% are observed. Temperature is extracted by fitting the second-harmonic experimental lineshapes to a spectral model.
Diffraction-limited imaging in a scanning transmission x-ray microscope
Authors: Jacobsen C. , Williams S. , Anderson E. , Browne M. , Buckley C. , Kern D. , Kirz J. , Rivers M. , Zhang X.
Published: February 2023

We report the characterization of a scanning transmission x-ray microscope which makes use of an undulator x-ray source, a high resolution scanning stage, and a 45 nm outer zone width, >10% diffraction efficiency Fresnel zone plate as the probe-forming optic at soft x-ray wavelengths (typically 3.64 nm). The modulation transfer function of the instrument is in good agreement with theory; it remains above 0.1 to spatial frequencies corresponding to structures as small as 25 nm. This spatial frequency limit is the best obtained in any soft x-ray microscope, and is about a factor of ten better than what is attained in conventional or confocal visible light microscopes. By deconvolving the zone plate point spread function from the image, the microscope has been used to resolve 36 nm features in a gold test object. The microscope is used primarily for the study of thick, hydrated biological specimens with minimal radiation dose.
Scattering from multilayer x-ray mirrors
Authors: Spiller Eberhard
Published: February 2023

Despite the fact that roughness of the boundaries reduces the reflectivity of normal incidence multilayer mirrors by a large factor for wavelengths λ < 100 Å, no loss in image quality from scattering has been observed up to now. Analysis of images of the solar corona give an upper limit on the amount of scattering, and we compare these results to data on the surface topography of the mirror surface and to measurements of scattering at λ = 1.54 Å. The data demonstrate the reduction in scattering from a multilayer structure when it is illuminated near the reflectivity maximum. We also compare the different measurement methods and show that the widely used rocking curve scan is not suitable to show this effect and to predict the performance of a mirror for imaging applications.
High reflectivity x-ray multilayers using reactive ion sputtering
Authors: Lund Mark W.
Published: February 2023

MOXTEK has been experimenting with reactive ion sputtering to achieve better quality multilayers. These experiments have been successful, achieving high reflectivities in the 8–60-Å region of the soft x-ray spectrum. These multilayers have been able to achieve >70% of their theoretical reflectivity. I present the results of x-ray, Auger, and atomic resolution TEM analysis of these multilayers.