bluuebunny/crossref_metadata_2025 huggingface dataset:
Applications of resonant photoacoustic spectroscopy
Authors: Röper J. , Frank K. , Hess P.
Published: February 2023

The apparatus employed consists of a laser as radiation source, a cylindrical resonator, and the signal processing system. The 3,39 µm or 1,15 µm beam of a He-Ne laser was intensity modulated by a chopper. The chopper frequency was continuously varied in an interval of 100 Hz around the selected acoustic resonance. In most measurements the first radial mode of the cylindrical sample cell was excited. The pressure change in the cell was detected with a small electret microphone. The microphone signals were preamplified and then a lock-in analyzer was employed for further signal processing. Both the linear change of the chopper frequency and the corresponding microphone signal were recorded simultaneously with a two channel recorder. It was possible, to make several succesive runs through the selected frequency interval to monitor a shift of the resonance frequency. In the dynamic mixing experiments, the shift of the resonance frequency was recorded as a function of time; in the energy transfer studies, the variation of the resonance frequency as a function of pressure was observed.
Photoacoustic Optical and Infrared Detector
Authors: Yun S. I.
Published: February 2023

In recent years there has been a rapid rise of interest in the photoacoustic (PA) effect and its applications in the investigation of gases, liquids, and solids1-17). The basic principles and the theory of the PA effect are now well established18–21). The primary source of the acoustic signal is the periodic heat flow from the sample to the surrounding gas, as the sample enclosed within a gas cell is cyclically heated by the absorption of chopped light. The periodic flow of this heat into the gas cell produces pressure fluctuations which are detected by a sensitive condenser microphone as an acoustic signal. The present research applies the technique of PA spectroscopy to the detection of the optical and infrared(IR) radiation itself. In PA energy conversion process, the thermal properties of the sample play an important role. Therefore this PA optical and IR detector can be classified as the thermal detector. The operation principle of this detector is different from those of presently available optical and IR detectors22-24). The sketch of PA optical and IR detector is shown in Fig. 1.
Photoacoustic Detection of Polarization-Dependent Nonlinear Optical Effects in Crystals
Authors: Bae Y. , Song J.J. , Kim Y.B.
Published: February 2023

Using photoacoustic detection technique, we have investigated two-photon absorption (TPA) effects in oriented single crystals, ZnS (hexagonal), ZnO and SrTiO3, with particular attention to the dependence of TPA on the frequency and polarization of the incident laser beam.
Particle Dynamics in Concentrated Settling Hard-Sphere Suspensions
Authors: Xue J.-Z. , Chaikin P.M. , Herbolzheimer E. , Rutgers M.A. , Russel W.B.
Published: February 2023

When the particles in a suspension are denser than the suspending solvent, their motions are controlled by sedimentation as well as the customary diffusion due to stochastic thermal fluctuations. As the particle concentration is increased, many-body hydrodynamic interactions strongly reduce the settling and diffusion[1,2]. Specifically, in a uniform concentrated suspension, the motion of the particles induces a compensating back flow of solvent which increases the average drag (i.e., reduces the diffusion and settling rates). However, the drag on any given particle is determined by the instataneous configuration of its neighbors. Therefore, the particles settle with a distribution of velocities, both vertically and horizontally, which on long time scales causes the particle to drift randomly. Recent computer simulations[3,4] and direct observations at low volume fraction in quiescent sedimentation experiments[5] show that the particles settle on the order of 100 interparticle distances before the microstructure rearranges sufficiently to decorrelate the particle velocities. Consequently, even in the absence of thermal fluctuations, on long time scales the particle motions become stochastic with an effective “diffusion” coefficient which is much larger than that due to Brownian motion.
Contaminant Characterization Through Light Scattering Angular Correlation
Authors: Videen Gorden , Pellegrino Paul , Pinnick R.G. , Ngo Dat
Published: February 2023

Recently, there has been a great deal of interest in light scattered by host droplets containing inclusions.1-5 One characteristic of such a system is a fluctuation in the scattered intensity. The nature of these fluctuations is not clear. They have been attributed to inclusions passing through regions of strong and weak electric fields within the host, like the hot-spot,1 and also to interference of the individual inclusions contained within the host droplet.4,5 The latter attributions of the scatter were used in previous photon-correlation analyses to determine the characteristics of the inclusions. However, the results of these analyses were not conclusive. We develop a novel technique for analyzing the scattering system in which we examine correlations between the signals at two scattering angles.
Morphological Characterization of Aggregates of Smoke Aerosols as Recognized by Light Scattering and Absorption Measurements
Authors: di Stasio S. , Massoli P.
Published: February 2023

Laser diagnostics and radiative heat transfer investigations on flame soot particulates appears to be seriously influenced by the a priori uncertainties connected to the lack of knowledge about the physical and chemical properties of the media under test. Both the uncertainty about soot refractive index [1] and [2],[3] morphology are demonstrated to substantially influence the effectiveness of optical in-situ scattering / absorption measurements.
Light Scattering by Radially Inhomogeneous Spheres to Study Droplet Evaporation
Authors: Massoli P.
Published: February 2023

In the last years, many optical systems, based on the measure of the properties of elastically scattered light, have been developed to determine in non intrusive way the velocity, the size and the optical properties of single droplets inside sprays. The Lorenz-Mie theory [1], which is strictly valid for homogeneous spheres, is usually used as base of these techniques. However, in real sprays, due to the heating of the droplets, the real part n of the refractive index of the liquid phase changes for the reduction of its density, while the imaginary part k increase if absorbing species are formed inside the droplets [2]. In these cases the Lorenz-Mie theory is not adequate and more sophisticated models to interpret the light scattering by inhomogeneous sphere must be employed.
Some Fundamentals of Surface Fluctuation Spectroscopy
Authors: Mann J. Adin.
Published: February 2023

The technology of surface light scattering spectroscopy1 involves hardware issues in measuring accurately the surface elevation ζq(t), autocorrelation function
Rq(t)def¯¯ζ
q
*(0)ζ
q
(t) or the corresponding spectrum,
G
q
(ω)=F^ς*
q
(0)ς
q
(t)[ω] where q is the wave number of the capillary wave spectrum and ω the frequency. Major issues include the optimization of the optical signal to noise, minimization of environmental noise and deconvolution of Rq(t) from the instrument function. This last issue is of special interest when measuring scattering from small patches wherein qσ < 20, σ is the Gaussian beam width parameter, as is the case when used with Brewster angle microscopy in overlapping footprints.
Diffuse Backscattering of Linearly Polarized Light from Biological Cell Suspensions
Authors: Hielscher Andreas H. , Mourant Judith R. , Bigio Irving J.
Published: February 2023

That polarization effects in scattered light can yield useful information about biological material has been shown as early as 1976, when Bickel et al. announced a “new biophysical tool".[1] Surprisingly, very few authors have used this new tool. Only a couple of studies exist that are concerned with polarization of forward scattered and transmitted light. [2-4] However, there are many biomedical applications where only backward scattered light is available for diagnostics, as, for example, in most endoscopic procedures. Recently Wang et al. addressed this issue for the first time by reporting angular variations of intensity in the diffuse- backscattered polarized light around the polarized-light input point.[5] In this study we investigate in detail the effects of particle sizes and concentration on the diffuse backscattering of linearly polarized light. We demonstrate that different particle size and concentrations lead to differences in the spatial pattern of backscattered light when viewed through a polarizer. These differences can be explained by Rayleigh and Mie theory, and can be used to characterize biomedical cells and tissues.
Spatial Modulational Instability in a Quadratic Medium: Theory and Experiment
Authors: Baboiu D.-M. , Fuerst R. , Lawrence B. , Torruellas W. E. , Stegeman G. I.
Published: February 2023

The stability of wave propagation has always been a major concern in nonlinear optics. The breakup of an intense monochromatic beam in a Kerr-type self-focusing medium was among the first nonlinear optical effects observed and is well-understood for third order nonlinear materials[1]. In geometries with two transverse dimensions, the nonlinear Schrodinger leads to catastrophic self-focusing (blow-up instability). Furthermore, one-dimensional solutions, when used in a geometry with two transverse dimensions, will also be subject to a large class of perturbations which lead to instabilities. Recently new origins for self-focusing effects have been observed in media with quadratic nonlinearities involving the strong coupling between a fundamental (FW) and a second harmonic (SH) beam.[2] The spatial instability properties of such a coupled two-beam system have not yet been investigated to date. Here we report a combined experimental and theoretical investigation of this phenomenon for quasi-one-dimensional beam inputs in a quadratic medium, KTP, near its phase-matching condition for second harmonic generation (SHG).
Fiber Optics Surface Light Scattering Spectrometer(FOSLSS)
Authors: Tin Padetha , Meyer William V. , Rogers R. , Mann J.A. , Cheung H. M. , Taylor T.
Published: February 2023

We have developed a surface light scattering spectrometer completely designed with optical fiber components only. To the best of our knowledge, this is the first demonstration of non-invasive measurement of the surface tension and viscosity of simple liquid/vapor interfaces with the fiber optics based sensor system.
Singular Value Inversion Applied to the Doppler Velocimetry Kernel
Authors: Rarity J. G. , Pike E. R. , Brown R. G. W.
Published: February 2023

We use a generalised matrix diagonalisation approach to obtain the singular system of the photon correlation laser Doppler-difference velocimetry kernel. We demonstrate inversion of simulated and real velocimetry data and compare this technique with earlier inversion methods using cubic spline based orthogonal functions.
Prism-Cell Laser Light-Scattering Spectrometer
Authors: Chu Benjamin , Xu Renliang
Published: February 2023

A prism-cell laser light-scattering (PCLLS) spectrometer capable of measuring the angular distribution of time-averaged scattered intensity at small scattering angles (2°≲ θ ≲ 13° at λo = 632.8 nm and n = 1.33, corresponding to 4600 cm" ≲ K ≲ 30000 cm-1, with K, λo and n being the magnitude of the scattering vector, the wavelength of light in vacuo and the refractive index of the scattering medium, respectively) by means of a linear intensified photodiode array (PDA) detector and simultaneous determination of intensity-intensity time correlation functions at two different scattering angles using two photomultiplier tube (PMT) detectors and associated digital photon correlators is described. The unique prism light-scattering cell also permits measurements of the refractive index of the scattering medium to better than one part in 106. The use of high quality optical glass in the entrance window and in the exit prism of the light-scattering cell for the incident laser beam, together with an aperture after the entrance window and in the scattering medium, results in a substantial reduction of the parasitic scattering along the light path. With the PDA and one of the PMTs mounted on a rotating arm, the angular ranges of our PCLLS spectrometer are limited mainly by optical geometry. For typical dilute aqueous solutions or suspensions, self-beating light-scattering measurements down to a scattering angle of 2° have been achieved. Measurements of self-beating linewidths for a polymer solution undergoing coil-to-globule transition are reviewed and some signal-to-noise ratio considerations for particle sizing in polymer solutions are presented.
Applications of Photon Correlation Techniques to Fermions
Authors: Silverman M. P.
Published: February 2023

The intensity correlation of fermion beams provides a novel interferometric approach, hitherto largely unexplored, to the investigation of the wave-like attributes, exchange symmetry, and interaction with potentials of multifermion states. Predicted quantum interference effects derive from the indistinguishability of particles as well as from the spatial separation of particle paths.
Electric Field-induced Decrease of Exciton Lifetime in GaAs Quantum Wells
Authors: Kash J.A. , Mendez E.E. , Morkoc H.
Published: February 2023

Previously1, it has been shown that c.w. photoluminescence (PL) at helium temperatures for excitons confined in quantum wells decreases sharply (i.e. is quenched) when an electric field is applied perpendicular to the layers. It was suggested there that the decrease might be due to spatial separation of the electrons and holes under the influence of the electric field. This separation would reduce the electron-hole spatial overlap, thus increasing the exciton radiative lifetime. In order to examine the luminescence quenching in more detail, we have measured the exciton PL decay directly.
The Permeable Base Transistor*
Authors: Murphy R. A.
Published: February 2023

The permeable base transistor (PBT) was conceived in 19791 and the first devices were fabricated shortly thereafter2. Numerical simulations predicted usable gains in the EHF frequency range3 and high speed performance in a logic circuit4. A three-dimensional drawing of a GaAs PBT showing a cutaway region is shown in Figure 1. The unique feature of a PBT is the thin tungsten grating of submicrometer periodicity (3200 Angstroms in the devices we have fabricated) embedded in the single-crystal GaAs. The tungsten grating separates the emitter layer from the collector layer and forms the base of the transistor. Because the tungsten forms a Schottky barrier with the GaAs, the voltage on the metal can be used to control the current flowing from the collector the emitter. The critical length of the control region is determined by the metallization thickness and the depletion width around the tungsten. Hence it can be made quite short, giving rise to the PBT's high frequency and high speed properties. In the device of Figure 1 proton bombardment is used to isolate and define the device and to provide insulating regions on which to fabricate contact pads.
Transmission Line Designs With a Measured Step Response of 3ps Per Centimeter
Authors: Kryzak Charles J. , Faris Sadeg M. , Meyer Kevin E. , Mourou Gerard A.
Published: February 2023

In order to effectively exploit the speed-high and high sensitivity potential of both superconducting and electro-optics technologies, proper generation, coupling and propagation of signals with bandwidths in excess of 100 Gigahertz is required. We report on extensive theoretical and experimental investigations of transmission lines of various configuration that was undertaken in order to find an optimum transmission medium which satisfies the ultra-wide bandwidth requirements. The investigation included various substrate thickness and dielectric constants as well as conductor material. We concluded that it is possible to realize transmission line designs capable of supporting bandwidths in excess of 100 Gigahertz if careful attention is paid to the generation and coupling of the ultra-wide bandwidth waveforms, i.e., taking into consideration the radiation and polarization of the fields set up by the generator as well as impedance matching between the generator and the line.
Ultrafast Optical Electronics: From Femtoseconds to Terahertz
Authors: Auston D. H. , Cheung K. P. , Valdmanis J. A. , Smith P. R.
Published: February 2023

The use of optical techniques to generate and measure fast electronic events is a challenging approach to high speed electronics with many important potential advantages relative to conventional electronic instrumentation.
Picosecond Pulse Generation in GaAlAs Lasers at a Repetition Rate of 18GHz
Authors: Lau K.Y. , Yariv A.
Published: February 2023

Significant progress has been made recently in operating semiconductor laser diodes at very high frequencies. The development of ultrafast semiconductor laser diodes [1] have extended the -3dB direct modulation bandwidth to above 10GHz. It will be shown in this paper that in addition to being useful as optical transmitters of microwave signals up to X-band frequencies, the recently developed ultra-high speed laser can be used to generate picosecond pulses at a frequency of 18GHz. The laser used is a window buried heterostructure laser on semi-insulating substrate[1]. The presence of the window near the end facet alleviates the problem of catastrophic damage and enable the laser to operate at very high optical power densities. The tight optical and electrical confinement along the length of the laser cavity (except at the window region) enables maximum interaction between the photon and electrons to take place and results in a very high direct modulation bandwidth. The -3dB direct modulation bandwidth of this device operating at 14mW is 12GHz. The intrinsic modulation response at 16GHz is approximately 13dB below the midband value. This loss in modulation efficiency can be compensated by coupling the laser to an external cavity of the appropriate length. The external cavity is composed of a short length of standard graded index multimode fiber of 50 μm core diameter, with a high refractive index hemispherical lens attached to one end of the fiber to facilitate coupling. The far end of a fiber is cleaved and is butted to a gold mirror. This induces a very sharp resonance in the modulation response of the laser. When the laser is driven on resonance by a microwave source whose power output is > 10dBm the optical modulation depth approaches unity and the optical waveform becomes pulse-like. Using an optical second harmonic generation autocorrelator the optical pulse width is found to be 12ps(FWHM). This, in effect, is active mode-locking of a laser diode at a repetition rate of 17.5GHz.
Cross Modulation of Light in SI Semiconductor Materials In the presence of Electric fields
Authors: Walpita L. M. , Chang W. S. C. , Wieder H. H. , Van Eck T.
Published: February 2023

Various optical devices are currently being investigated for optical signal processing and communication[1,2]. In this paper we will discuss cross modulation of light observed in semiconductor materials. This effect could potentially be used to obtain optical logic functions such as AND gate.
An Ultrafast Diffusion-Driven Detector
Authors: Kostenbauder A.G. , Siegman A.E.
Published: February 2023

Numerous fast semiconductor photodetectors have been developed in the last decade. These devices have used short carrier lifetimes1,2 or large electric fields and small geometries3,4 to produce fast impulse responses. In contrast to these methods of making fast photodetectors, we propose a photovoltaic device whose operating speed is due to diffusion of carriers. This device involves interfering light waves to form a grating of photoexcited carriers with a sinKx spatial dependence. Such a distribution will decay with a time constant of (DK2)−1, where D is the material’s diffusion constant. Because K can be made very large, the response time can be extremely short. If the grating is formed in silicon, for example, with optical beams of 1 μm wavelength having antiparallel k-vectors, then the diffusion-driven detector response time will be 0.25 psec.
Kilovolt Sequential Waveform Generation by Picosecond Optoelectronic Switching in Silicon
Authors: Chang C. S. , Rhee M. J. , Lee Chi H. , Rosen A. , Davis H.
Published: February 2023

Several methods for generating the RF sequential waveform have been demonstrated [1,2]. A frozen wave generator, a simple and efficient device [2], consists of many segments of transmission lines connected by switches in series. When the switches in the generator are closed simultaneously, the “frozen waves” which are charged inside the segments of the transmission line will be brought out sequentially. We have demonstrated in the previous paper [3] the generation, using three silicon switches, of a sequential pulse of two and one half cycles (250 MHz) having a rise time in picoseconds region. However, due to the limited high voltage handling capability of the switches, previous experiments [1,2,3] are not easily extended to the kilovolt applications.
A New Optoelectronic CW Microwave Source
Authors: Clark C.J. , Chauchard E.A. , Webb K. , Zaki K. , Lee C.H. , Polak-Dingles P. , Hung H-L.A. , Huang Ho C.
Published: February 2023

Ultrafast switching utilizing picosecond photoconductors finds many applications, including optoelectronic sampling and characterization of high speed electronic devices [1]. One of the major areas of applications that has not been explored is in microwave and millimeter-wave generation and control. The jitter-free switching characteristic of these devices is very promising since the microwave or millimeter wave signals can be generated in complete time synchronization with the exciting optical pulses. The time synchronization opens the way to unique applications.
Longitudinally Localized Optical Carrier Injection for Femtosecond Transport Studies
Authors: Downer M.C. , Reitze D.H. , Zhang T.R.
Published: February 2023

A new generation of microelectronic devices will be based on ballistic and quantum tunneling transport processes, which involve transit times on a femtosecond scale across submicron semiconductor layers. Fundamental experimental studies of these phenomena will require the use of femtosecond optical techniques to inject and probe carriers locally, just as analogous picosecond techniques have been used in studying slower transport processes in thicker layers1,2. However, because optical absorption (and therefore carrier injection) depths at near band gap wavelengths (typically 1μm.) greatly exceed the thickness of the semiconductor layers in which most femtosecond transport phenomena occur (typically .01 to 0.1 μm.), adequate spatial resolution to observe these processes directly has not been achievable. We introduce a new technique for optically injecting carriers of any desired energy within the first few hundred angstroms of the surface of a semiconductor layer with femtosecond time resolution, so that the evolution of femtosecond transport processes can be resolved.
Optical Reading of InGaAs Modulation Doped Field Effect Transistor
Authors: Bar-Joseph I. , Chemla D. S. , Klingshirn C. , Miller D. A. B. , Kuo J. M. , Chang T. Y.
Published: February 2023

We present the first observation of absorption quenching in a semiconductor quantum well by electrical control of the carrier density. We have observed this novel effect at room temperature in a single modulation-doped InGaAs quantum well which was used as the conducting channel of a field effect transistor (FET). The effect is extremely large and we have used it for direct optical determination of the state of the FET.
Photoemissive Testing of High-Speed Electrical Waveforms
Authors: Weiner A. M. , Marcus R. B. , Lin P. S. D. , Abeles J. H.
Published: February 2023

Photoemissive sampling was recently introduced as a new, contactless method for probing high-speed electrical waveforms on circuits and devices on any semiconductor [1-3]. Previously the best temporal resolution achieved was limited to 40-psec. In this paper we describe photoemissive sampling measurements which demonstrate a temporal resolution below 7-psec.
Electro-Optic Sampling of High-Speed, InP-Based Integrated Circuits
Authors: Wiesenfeld J. M. , Tucker R. S. , Antreasyan A. , Burrus C. A. , Taylor A. J.
Published: February 2023

We report the application of electro-optic sampling[1-3] to measurements of waveforms internal to a high-speed InP integrated circuit. This is possible because InP is an electro-optic material with electro-optic coefficient comparable to that of GaAs. Waveforms and propagation delays through a two stage InGaAs/InP metal-insulator-semiconductor FET (MISFET) inverter circuit[4,5] have been measured. The observed propagation delay through an individual FET is 21±7 ps. The measurement uses an electro-optic sampling system based on a 1.3 μm InGaAsP injection laser[3] that is gain-switched. This work extends to InP-based circuits previously developed techniques for non-invasive sampling using the electro-optic effect in GaAs[2].
Multigigahertz Logic Based on InP-MISFET’s Exhibiting Extremely High Transconductance
Authors: Antreasyan A. , Garbinski P. A. , Mattera V. D. , Temkin H.
Published: February 2023

InP metal4nsulator-semiconductor field-effect transistors (MISFET) offer significant potential in high-speed digital circuits1 and high-frequency power devices2. This is due to the high saturation velocity and mobility of electrons in InP. In addition, metal-semiconductor field-effect transistors cannot be realized on Ga0.47In0.53 As as a result of the low Schottky barrier. The fabrication of InP MISFET’s has turned out to be difficult in the past3 due to the formation of surface defects at the dielectric-semiconductor interface. In this paper we report a novel, high-speed, ultra high transconductance Ga0.47In0.53 As / InP MISFET. The devices exhibit a propagation delay of 25 ps/stage and extrinsic dc transconductances as high as 320 mS/mm for a gate length of 1 μm. These are to our knowledge the highest transconductance and the lowest propagation delay measured with an FET on an InP substrate. High-speed digital circuits based on these MISFET’s are capable of operating at 5 GHz.
Picosecond Photoconductive Transcievers
Authors: DeFonzo Alfred P. , Lutz Charles R. , Jarwala Madhuri
Published: February 2023

Recent studies [1,2,3] of electromagnetic transients from gap discontinuities in microstrip structures driven by picosecond and subpicosecond photoconductive currents indicate a potential for using optical means for generating and detecting milllimeter waves. It has been demonstrated [ ]that short coherent burst of radiation with wavelength components in the millimeter and submillimeter range can be used to perform fundamental studies of materials suitable for a variety of uses including: electro-optic samplers, modulators and millimeter wave circuits. It is desirable to have more sophisticated antenna elements than gap discontinuities that can provide a greater degree of control of the space and time distribution of photoconductively generated and detected radiation. To be of general use, it is also desirable that such antennas be of a size comparable to other device elements found in integrated millimeter wave cicuits and be fabricated on standard substrate materials using planar technology.
Picosecond switching in Josephson tunnel junctions
Authors: Sobolewski R. , Dykaar D.R. , Hsiang T.Y. , Mourou G.A.
Published: February 2023

In this work we have followed our earlier attempts to apply the electro-optic sampler to superconducting electronics,1 and developed a fully cryogenic electro-optic sampler by integrating and immersing in superfluid helium both the photo-conductive switch and the birefringent lithium tantalate sensor. The ultimate temporal response of the system2 as determined by measuring the transient onset of photoconductivity in a GaAs switch was less than 400 fs. The system was arranged in to two different configurations and used to probe the switching of a 30 × 30 μm2 Josephson tunnel junction.
Carrier Lifetime vs. Ion-Implantation Dose in Silicon on Sapphire
Authors: Doany F. E. , Grischkowsky D. , Chi C.C.
Published: February 2023

The generation of subpicosecond electrical pulses has recently been demonstrated using fast photoconductive switches driven by short laser pulses [1]. In these measurements electrical pulses on the order of 0.6 ps were obtained by shorting a charged transmission line fabricated on an ion-implanted silicon-on-sapphire (SOS) wafer. The major factors determining the shape and duration of these electrical pulses were the laser pulsewidths, the circuit characteristics of the photoconductive gaps and the transmission line, and the carrier lifetime of the semiconductor [2]. Since laser pulses shorter than 100 fs are routinely obtained from colliding-pulse-modelocked dye lasers, the laser pulsewidth can be made negligible compared to the generated electrical pulse. In addition, the limiting factors on the time response due to the circuit reactance may be eliminated if the capacitance of the generation site is reduced to negligible amounts. Under these conditions the duration of the electrical pulse would be mainly determined by the carrier lifetime in the ion-implanted SOS. However, no systematic measurements of this lifetime are available.
High Speed Opto-Isolator for Radar Applications
Authors: Anthes J.P. , Garcia P. , Lau K.Y. , Ury I.
Published: February 2023

We have designed, fabricated and tested a high speed opto-isolator utilizing state-of-the-art optoelectronic components operating at frequencies up to 6 GHz. This opto-isolator will be an indispensible component in modem radar systems and is used for preventing frequency-pulling of a low power oscillation due to reflected signals.
A Simple Technique to Generate or Gate Microwave Pulses with Picosecond Speeds
Authors: Margulis W. , Grivitskas V. , Adomaitis E. , Dobrovolskis Z. , Krotkus A.
Published: February 2023

A number of articles have recently been published (1-4) where microwave signals are switched and controlled by means of a ps photoconductor illuminated by a mode-locked laser pulse. The advantages of such an approach over conventional electronic circuitry include higher speeds, excellent timing and high power capability. Here we describe a simple arrangement which makes it possible to both switch an arbitrary number of cycles from a microwave generator (case 1), as well as to shape microwave pulses from a dc bias source (case 2), with easily adjustable frequency and duration. To that end we use a ps photoconductor with a PEPS (5), which controls the pulse produced.
Modulation Efficiency Limited High Frequency Performance of the MODFET
Authors: Foisy M.C. , Huang J.C. , Tasker P.J. , Eastman L.F.
Published: February 2023

Epilayer design for the MODFET is frequently performed using the depletion approximation [1,2]. The work of authors such as Ponse et. al. and Stern and Das Sarma have provided tools by which electron distributions and capacitances can be calculated without this assumption [3,4]. They demonstrate that for two dimensional electron gas (2DEG) sheet concentrations significantly below the saturation saturation value, free and bound electrons are present in the supply layer. Because these electrons must be modulated with the 2DEG electrons, the gate capacitance is increased while the transconductance is decreased [5]. The unity current gain frequency, fT, is thus decreased.
Timing Jitter in Repetitively Pulsed Semiconductor Lasers
Authors: Yuan Ruixi , Taylor Henry F.
Published: February 2023

Timing jitter can limit the accuracy of data obtained by optical sampling using repetitively pulsed semiconductor lasers. When the optical sampling is used for real-time analog-to-digital conversion, for example, the maximum allowable jitter is typically 20-40 times less than the maximum permissible pulse width1. Timing jitter in semiconductor lasers has been studied experimentally2,3, but a predictive model has not heretofore been available.
Picosecond Pulse Generation and Sampling with GaAs Monolithic Integrated Circuits
Authors: Marsland R. A. , Madden C. J. , Valdivia V. , Rodwell M. J. W. , Bloom D. M.
Published: February 2023

We have developed a GaAs nonlinear transmission line pulse generator capable of producing a 6 V, 1.6 ps falltime electrical transient. We have also developed a monolithic diode sampling bridge which, when driven by a nonlinear transmission line, has a bandwidth in excess of 128 GHz.
Investigation of Picosecond Time-Resolved Photoluminescence in Gallium Arsenide with 3-μm Spatial Resolution
Authors: Louis Thomas A.
Published: February 2023

A novel instrument has recently been developed for picosecond time-resolved photoluminescence (TRPL) investigation of GaAs with 3 μm spatial resolution : the Photoluminescence Lifetime Microscope Spectrometer (PLμS). The PLμS is based on time-correlated single photon counting (TCSPC) with a single photon avalanche diode (SPAD) detector. Sensitivity of the PLμS, especially in the near infrared wavelength region (800-1000nm), is several orders of magnitude better than for synchroscan streak cameras. A signal-to-noise ratio of better than 1000:1 is typically obtained from a GaAs sample region of 3 μm diameter at room temperature and at excess carrier densities (at peak excitation) as low as 1015cm-3. As a result of the very low optical power requirements, a pulsed diode laser can be used as the excitation source. All signals are conveniently handled via optical fiber, which makes the PLμS a unique instrument for routine assessment of semiconductor materials and devices in an industrial environment.
Spectral Filtering of Relaxation Oscillations in Injection-Current-Modulated Diode Lasers
Authors: Basu Santanu , May Paul G. , Halbout Jean-Marc
Published: February 2023

Spectrally resolved pulse shapes from injection current modulated Fabry-Perot diode lasers have been obtained using a streak camera. The results indicate that the relaxation oscillations are spectrally separated from the primary pulse. Spectral filtering was carried out to produce single-longitudinal-mode output free of relaxation oscillations.
High-Speed Lightwave Systems
Authors: Gnauck Alan H.
Published: February 2023

The status of multigigabit direct-detection lightwave systems is reviewed, with an emphasis on the potential and limitations of present system components.
Picosecond GaAs-Based Photoconductive Optoelectronic Detectors
Authors: Smith F. W. , Le H. Q. , Frankel M. , Diadiuk V. , Hollis M. A. , Dykaar D. R. , Mourou G. A. , Calawa A. R.
Published: February 2023

Picosecond photoconductive-switch performance was demonstrated with a novel material deposited by molecular beam epitaxy at low substrate temperatures using Ga and As4 beam fluxes. For a photoconductive-gap switch fabricated on a coplanar transmission line, the speed is 1.6 ps (full width at half maximum) and the voltage response is 10 to 100 times greater than that of conventional photoconduc­tive switches. Since LT GaAs is compatible with GaAs device and IC technologies, this photoconduc­tive switch may find extensive use in high-speed device and circuit testing.
20-ps Resolution Single-Photon Solid-State Detector
Authors: Ghioni M. , Lacaita A. , Cova S. , Ripamonti G.
Published: February 2023

Single Photon Avalanche Diodes (SPADs) are avalanche photodiodes specifically designed for reverse bias operation above the breakdown voltage (Geiger-mode operation), and used for detecting single optical photons. Studies were performed to relate the attainable timing resolution to the device geometry and operating conditions. A new silicon device structure was designed in order to obtain improved timing performance with respect to previous SPADs.

Extensive tests were carried out in order to ascertain the timing resolution of the device in time-correlated photon counting. The SPAD timing resolution, in terms of its full-width at half­maximum (FWHM) contribution to the overall instrumental response width, is 20 ps with the detector cooled to -65 C, and 28 ps at room temperature. This is the highest resolution so far reported for solid-state single-photon detectors.

Among vacuum tubes, comparable results are obtained only with special microchannel-plate photomultipliers (MCP-PMT). With the excellent timing resolution of the SPAD and the well-known advantages of Time Correlated Photon Counting systems (high sensitivity, linearity etc.), various applications are foreseen in areas so far dominated by streak cameras.
Photocurrent-Voltage Characteristics of Ultrafast Photoconductive Switches
Authors: Moss S. , Knudsen J. , Bowman R. , Adams P. , Smith D. , Herman M.
Published: February 2023

We report measurements of photocurrent-voltage characteristics of ultrafast photoconductive switches fabricated on gallium arsenide, silicon with a buried oxide layer, and silicon-on-sapphire.
Characterization of Optically Pulsed Millimeter-Wave Antennas
Authors: Lutz Charles R. , DeFonzo Alfred P.
Published: February 2023

We describe experiments in which optoelectronic sampling techniques are used to investigate the transient response of integrated millimeter wave antenna elements. The internal device characteristics are analyzed by performing wide bandwidth time domain reflectometery measurements over a frequency span exceeding 200 GHz. In addition, we demonstrate a novel approach to measuring the transient far-field radiation patterns emitted from these devices. The far-field patterns in both the E and H Planes are observed to consist of single forward directed lobes which are shown to have a cosine-squared dependence.
Electric-Field Dependence of the Tunneling Escape Time of Electrons from a Quantum Well
Authors: Norris T. B. , Song X. J. , Wicks G. , Schaff W. J. , Eastman J. , Mourou G. A.
Published: February 2023

Using time-resolved photoluminescence we have directly measured the rate at which electrons tunnel from a quantum well through a thin barrier in the presence of an applied electric field.
Electron Tunneling Time Measured by Photoluminescence Excitation Correlation Spectroscopy
Authors: Jackson M. K. , Johnson M. B. , Chow D. H. , Soderstrom J. , McGill T. C. , Nieh C. W.
Published: February 2023

The tunneling time for electrons to escape from the lowest quasi-bound state in the quantum wells of GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures with barriers between 16 Å and 62 Å has been measured at 80 K using photoluminescence excitation correlation spectroscopy. The decay time for samples with barrier thicknesses from 16 Å (≈ 12 ps) to 34 Å (≈ 800 ps) depends exponentially on barrier thickness, in good agreement with calculations of electron tunneling time derived from the energy width of the resonance. Electron and heavy-hole carrier densities are observed to decay at the same rate, in contrast to resonance-width calculations that indicate that heavy-hole tunneling times should be much longer than those for electrons. Reasons for this observation are discussed. Similar measurements in biased structures showing negative differential resistance are described.
Phonons and Phonon Interactions in Layered Semiconductors
Authors: Mahler G. , Kriman A. M. , Ferry D. K.
Published: February 2023

Continuum models are developed which describe the optical as well as the acoustic displacements in polar media, including corrections to the harmonic approximation. These lead to simple phonon modes in locally isotropic media, and confirm a previously conjectured dispersion relation. They are used to study phonon lifetimes and the effects of heterostructure confinement. It is found that the lifetime of confined LO phonons decaying into delocalized acoustic phonons is substantially independent of size of the confining region.
Two-Dimensional Field Mapping of GaAs Microstrip Circuit by Electro-optic Sampling
Authors: Li Ming G. , Chauchard Eve A. , Lee Chi H. , Hung Hing-Loi A.
Published: February 2023

Electro-optic sampling is a useful technique to study the electric field distribution in a GaAs microstrip circuit.[1] It has an extremely wide bandwidth capability and, can perform the measurement without physical or electrical contact to the device. However, most of the results of the experiments that had been reported were only point measurement; measuring the electric field at one particular point or discrete locations in the circuit. For some applications, this measurement does not provide adequate information. Two dimensional field distribution can be easily measured by electro-optic sampling because of its noncontact feature. W. Donaldson performed a 2-dimensional measurement with a 2-dimensional diode array[2]. After the polarized incoming light interacted with the electric field, the image of the reflected light which carried the field distribution information was focused on to a 2-dimensional diode array. The acquired data were then displayed on a computer monitor. This method has very good temporal resolution, but very low sensitivity. It requires a high power laser and can only measure strong electric field. These limit its application, making the method unsuitable for characterizing a regular GaAs device.
GaAs Based Very Fast Optoelectronics
Authors: Kamiya Takeshi
Published: February 2023

Adding to the success of optoelectronics in fiber-optic transmission and optical recording, there still remains a challenging peak of optical information processing. Introduction of optical technology in the field of information processing will be justified when the intrinsic properties of optical media such as very fast response (1) and parallelism (2) are fully exploited. A series of fundamental researches have been made along the line of all optical processing, where replacement of all the electronic devices with optical devices should help getting rid of RC time constant constraints. This approach, however, turned out to be rather futuristic, in the sense that there still remain too many premature components yet to be developed before the total ultrafast pure optical signal processing system will be brought to reality.
Femtosecond Spatio-Temporal Field Measurements in GaAs Quantum Wells
Authors: Knox W.H. , Doran G.E. , Cunningham J. , Goodnick S.M.
Published: February 2023

The exciton in quantum wells is a sensitive detector of electric fields. This field response has been used recently to detect ultrafast electrical transients in ultra-thin quantum well coplanar striplines with time resolution as fast at 180 fs [1]. In these experiments, it is found that the field in the gap is not uniform [2]. In such as case, it is interesting to use the spatial resolution of the excitonic electroabsorption effect to obtain space-time resolved electrical transient information. In the experiments, we use an infrared CPM dye laser operating at 820 nm wavelength [3], which is coincident with the exciton energy. The pump beam is focused into a 10 micron coplanar stripline which is patterned on the sample. The sample consists of a 0.4 micron thick layer of GaAs-AlGaAs quantum wells and a 0.35 micron thick AlGaAs stop etch layer. The substrate is etched out, leaving a 0.75 micron thick free-standing film. This structure has interesting high frequency propagation characteristics such as propagation speed of 82 % the speed of light, and low dielectric loss, radiation losses and modal dispersion [1,4]. The pump beam creates an ultrafast electrical transient which propagates in the coplanar stripline (Figure 1, inset). We probe the signal by focusing a delayed probe pulse through the stripline further down the line at the desired distance. In the present case, we investigate the spatial distribution of the field transient, as viewed by the quantum well excitons, which give a microscopic reading of the conditions in the structure. Figure 1 shows a result of focusing the probe beam to a 1 micron diameter spot and scanning the time delay at various positions in the gap.
Transient Absorption of Low-Temperature-MBE-Grown GaAs
Authors: Norris T.B. , Sha W. , Schaff WJ. , Song X.J.
Published: February 2023

MBE growth of GaAs is normally performed at a substrate temperature around 600 °C. It has recently become apparent, however, that GaAs grown at lower temperatures (LT GaAs) has some very interesting and useful properties. The material was first grown as a buffer layer to eliminate backgating in GaAs MESFET's, taking advantage of the high resistivity of this material [1]. Subsequently the LT GaAs was investigated as a photoconductive detector, where a response recovery of as short as 600 fs was observed [2]. The promise of this material for fast photoconductive devices has motivated a study of the carrier dynamics in LT GaAs. Gupta et al. [3] have investigated the time-resolved reflectivity of LT GaAs in an attempt to determine the carrier lifetime. Their sample was excited and probed high in the conduction band (at 620 nm), however, so interpretation of the results is not entirely straightforward. Therefore, we have performed transient absorption spectroscopy of the band-edge region of LT GaAs to directly determine the carrier dynamics.
Strained-Layer Electronics and Optoelectronics
Authors: Myers David R.
Published: February 2023

Strained-layer epitaxy involves more than the dislocation-free growth of dissimilar materials: effective strained-layer epitaxy exploits lattice-mismatch-induced strain to fine-tune material properties. This paper describes strained-layer epitaxy and describes its application to electronic and optoelectronic device to improve performance.
Optimisation of packaged, actively mode-locked 1.5 μm InGaAsP diode laser for >10 Gbit/s OTDM transmission systems
Authors: Marshall I.W. , Constantine P.D. , Lowery A.J. , Cooper D.J. , Elton D.
Published: February 2023

Work on transatlantic communications systems has already shown [1] that the maximum bit-rate/distance product for any system length is always obtained by transmitting well spaced transform limited pulses (solitons), e.g. 20 ps pulses for 10 Gbit/s transmission over 5000 km [2]. In a 40 Gbit/s network similar techniques would allow transmission over 1-2000 km using 3-5 ps pulses [3]. The principal barrier to development of such systems has always been the lack of a suitable pulse transmitter, which must produce high power, transform limited ps pulses at GHz rates, and must also be portable and stable for long periods (years). Recently it has been shown that suitable pulses can be generated by optically amplified semiconductor laser sources [4-6], similar to those used in current lightwave transmission systems. Two techniques have been used; gain switching and filtering [4],which is simple to implement but produces substantial pulse to pulse jitter, and mode-locking [5,6], which produces better pulses but is subject to stability problems. In this paper we show for the first time that the mechanical problems associated with external cavity mode-locked lasers can be overcome, without compromising on output pulse quality, by building a packaged cavity, and that the important operating parameters are amenable to external control for long term stability.