TRAPATT oscillations in a p-i-n avalanche diode
P-i-n avalanche diode trapped plasma avalanche triggered transit /TRAPATT/ oscillations characteristics and voltage waveform under square wave driving current, using computer program
Parker, D.↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Ogo 5 magnetic-field data near the earth's bow shock - A correlation with theory.
Magnetic-field data obtained in the earth's bow-shock region with a high-resolution triaxial fluxgate magnetometer aboard the Ogo 5 satellite have been correlated with a theory of Tidman and Northrop (1968). These authors have shown that either of two hypotheses about the nature of low-frequency magnetic waves could be invoked to explain previous observations. We have observed exponentially decaying upstream waves that are consistent with only one of these hypotheses. This observation allows use of the theory to infer the local shock velocity and frequency of driving currents within the shock. This method of finding the shock velocity is less sensitive to errors in the plasma parameters than is the method based on the Rankine-Hugoniot relations.
Guha, J. K.↗
Concepts of magnetospheric convection
The paper describes the basic theoretical notions of convection applicable to magnetospheres in general and discusses the relative importance of convective and corrotational motions, with particular reference to the comparison of the earth and Jupiter. The basic equations relating the E, B, and J fields and the bulk plasma velocity are given for the three principal regions in magnetosphere dynamics, namely, the central object and its magnetic field, the space surrounding the central object, and the external medium outside the magnetosphere. The notion of driving currents of magnetospheric convection and their closure is explained, while consideration of the added effects of the rotation of the central body completes the basic theoretical picture. Flow topology is examined for the two cases where convection dominates over corotation and vice versa.
Vasyliunas, V. M.↗
Single-mode laser studies: Design and performance of a fixed-wave length source and coupling of lasers to thin-film optical waveguides
A module developed for the generation of a stable single wavelength to be used for a fiber optic multiplexing scheme is described. The laser is driven with RZ pulses, and the temperature is stabilized thermoelectrically. The unit is capable of maintaining a fixed wavelength within about 6 A as the pulse duty cycle is changed between 0 and 100 percent. This is considered the most severe case, and much tighter tolerances are obtainable for constant input power coding schemes. Using a constricted double heterostructure laser, a wavelength shift of 0.083 A mA is obtained due to laser self-heating by a dc driving current. The thermoelectric unit is capable of maintaining a constant laser heat-sink temperature within 0.02 C. In addition, miniature lenses and couplers are described which allow efficient coupling of single wavelength modes of junction lasers to thin film optical waveguides. The design of the miniature cylinder lenses and the prism coupling techniques allow 2 mW of single wavelength mode junction laser light to b coupled into thin film waveguides using compact assemblies. Selective grating couplers are also studied.
Ladany, I.↗
Theory of plasma waves in the auroral E region
A general theory is developed for both electrojet waves and ion cyclotron and current convective waves observed above 120 km altitude. Previously defined electrojet instability theories are extended to encompass the effects of the magnetic field on ions and the presence of field-aligned currents. The ion-cyclotron (E) waves are assumed produced by the two-stream instability in regions dominated by ion magnetization effects. Field-aligned and cross-field currents drive the E waves, which have displayed threshold drift velocities (TDV) sensitive to conditions at altitudes with effective electron/ion and anomalous electron collision frequencies. The electron density gradients in the region affect the magnitude of the TDV for waves on scales of tens of meters. Recombinational damping increases the TDV for marginal damping of two-stream E waves and establishes a TDV for excitation of large-scale gradient drift waves which propagate nearly perpendicularly to the magnetic field and may have only 10-20 m wavelengths.
Fejer, B. G.↗
High voltage power supply
A high voltage power supply is formed by three discrete circuits energized by a battery to provide a plurality of concurrent output signals floating at a high output voltage on the order of several tens of kilovolts. In the first two circuits, the regulator stages are pulse width modulated and include adjustable ressistances for varying the duty cycles of pulse trains provided to corresponding oscillator stages while the third regulator stage includes an adjustable resistance for varying the amplitude of a steady signal provided to a third oscillator stage. In the first circuit, the oscillator, formed by a constant current drive network and a tuned resonant network included a step up transformer, is coupled to a second step up transformer which, in turn, supplies an amplified sinusoidal signal to a parallel pair of complementary poled rectifying, voltage multiplier stages to generate the high output voltage.
Ruitberg, A. P.↗
Monitoring The Atmosphere By Diode-Laser Spectroscopy
Report describes state of art of tunable-diode-laser second-harmonic spectroscopy applied to measurements of concentrations of trace constituents of atmosphere. Combination of temperature, composition, and drive-current tuning, wavelengths of tunable diode lasers varied over infrared range of 3 to 30 micrometer, containing spectral lines of many molecules of interest in atmospheric research.
Loewenstein, Max↗
Exospheric temperatures during solar cycle 22
An analysis is conducted of the orbital decay of the Long Duration Exposure Facility (LDEF) satellite in order to develop an empirical model of the solar radio flux at 10.7 cm and of the exospheric temperature driving current atmospheric-density models at high radio fluxes. The Jacchia-Lineberry (1982) atmospheric model is used to fit a set of orbit semimajor axis observations to a predicted set whose only free variable was the exospheric temperature. A comparison of the exospheric temperatures with those predicted by the Jacchia (1977) model indicates increasing divergences above 1100 K, suggesting needed modifications to the model.
Badhwar, Gautam D.↗
Self-consistent analysis of lattice-matched and pseudomorphic quantum-well emission transistors
A self-consistent analysis of the quantum-well emission transistor (QWET) is presented allowing an exact calculation of the device quantum properties. Poisson's and Schroedinger's equation are solved numerically using a finite-difference method on a self-consistent basis. Pseudomorphic AlGaAs/InGaAs designs with 15-20 percent excess In are suggested for improving the device performance. Design with doping in various parts of the QWET are also studied. This analysis reveals that the device performance is less optimistic than previously predicted by analytic approaches. By introducing the pseudomorphic channel principle, while maintaining a reasonably low Al content for the gate and collector layers, it is, however, possible to obtain satisfactory performance. Optimum pseudomorphic designs showed high current driving capability (200,000 A/sq cm), high transconductance (3S/mm), and small intrinsic delay time (2 ps).
Hong, Kyushik↗
Phase stability of injection-locked beam of semiconductor lasers
An experiment on the phase stability of an injection locked beam was done by using AlGaAs semiconductor lasers. The coherence of two beams from master and slave lasers was measured by interference between the beams in the Twymann-Green interferometer. The phase change of the output beam of the slave laser as a function of the driving current was measured in a Mach-Zehnder interferometer consisting of the master and slave lasers, and a value of 2.5 radians/mA was obtained.
Kwon, Jin Hyuk↗
Improved Circuit For Hot-Film Anemometer
Circuit suitable for automation or computer control of setup and operation. Hot-film or hot-wire anemometer circuit features individual current drives for two arms of wheatstone bridge, plus other features that provide improved calibration and automated or computer-controlled operation.
Gray, David L.↗
Development of simplified external control techniques for broad area semiconductor lasers
The goal of this project was to injection lock a 500 mW broad area laser diode (BAL) with a single mode low power laser diode with injection beam delivery through a single mode optical fiber (SMF). This task was completed successfully with the following significant accomplishments: (1) injection locking of a BAL through a single-mode fiber using a master oscillator and integrated miniature optics; (2) generation of a single-lobed, high-power far-field pattern from the injection-locked BAL that steers with drive current; and (3) a comprehensive theoretical analysis of a model that describes the observed behavior of the injection locked oscillator.
Davis, Christopher C.↗
High bandwidth electro-optic technology for intersatellite optical communications
The research and development of electronic and electro-optic components for geosynchronous and low earth orbiting satellite optical high bandwidth communications at the NASA-Goddard Space Flight Center is reviewed. Intersatellite optical communications retains a strong reliance on microwave circuit technology in several areas - the microwave to optical interface, the laser transmitter modulation driver and the optical receiver. A microwave to optical interface is described requiring high bandwidth electronic downconverters and demodulators. Electrical bandwidth and current drive requirements for the laser modulation driver for three laser alternatives are discussed. Bandwidth and noise requirements are presented for optical receiver architectures.
Krainak, Michael A.↗
Final Design and Integration of Micro-Chip Inductive Edge Sensors for the Seven Segment Demonstrator. Testing of Integrated Edge Sensors in Test Packages
The contractor attended the critical design review and evaluated the presentations of other team members and presented data on the inductive edge sensor. The prototype micro-chip inductive edge sensor was evaluated, and devices were found to have a number of characteristics which made them unsuitable for installation on the seven segment demonstrator. The amplifier bandwidth was too low, the output drive current was too small, and there is an interaction between the digital circuitry and the amplifier that causes the amplifier to stop functioning. Therefore, the inductive edge sensors were not installed on the seven segment demonstrator. The contractor has participated in instruction, problem analysis, and provided technical assistance to NASA and its contractors for the development of 8 hexagonal mirror faceplates with electronics and edge sensors.
Karpinsky, John↗
Single Frequency, Pulsed Laser Diode Transmitter for Dial Water Vapor Measurements at 935nm
We report a tunable, single frequency, narrow linewidth, pulsed laser diode transmitter at 935.68nm for remote sensing of atmospheric water vapor. The transmitter consists of a CW, tunable, external cavity diode laser whose output is amplified 2OdB using a tapered diode amplifier. The output is pulsed for range resolved DIAL lidar by pulsing the drive current to the diode amplifier at 4kHz with a .5% duty cycle. The output from the transmitter is 36OnJ/pulse and is single spatial mode. It maintains a linewidth of less than 25MHz as its wavelength is tuned across the water vapor absorption line at 935.68nm. The transmitter design and its use in a water vapor measurement will be discussed.
Switzer, Gregg W.↗
Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices
We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction to the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion or quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.
Biegel, Bryan A.↗
Hierarchical Statistical 3D ' Atomistic' Simulation of Decanano MOSFETs: Drift-Diffusion, Hydrodynamic and Quantum Mechanical Approaches
When MOSFETs are scaled to deep submicron dimensions the discreteness and randomness of the dopant charges in the channel region introduces significant fluctuations in the device characteristics. This effect, predicted 20 year ago, has been confirmed experimentally and in simulation studies. The impact of the fluctuations on the functionality, yield, and reliability of the corresponding systems shifts the paradigm of the numerical device simulation. It becomes insufficient to simulate only one device representing one macroscopical design in a continuous charge approximation. An ensemble of macroscopically identical but microscopically different devices has to be characterized by simulation of statistically significant samples. The aims of the numerical simulations shift from predicting the characteristics of a single device with continuous doping towards estimating the mean values and the standard deviations of basic design parameters such as threshold voltage, subthreshold slope, transconductance, drive current, etc. for the whole ensemble of 'atomistically' different devices in the system. It has to be pointed out that even the mean values obtained from 'atomistic' simulations are not identical to the values obtained from continuous doping simulations. In this paper we present a hierarchical approach to the 'atomistic' simulation of aggressively scaled decanano MOSFETs. A full scale 3D drift-diffusion'atomostic' simulation approach is first described and used for verification of the more economical, but also more restricted, options. To reduce the processor time and memory requirements at high drain voltage we have developed a self-consistent option based on a thin slab solution of the current continuity equation only in the channel region. This is coupled to the Poisson's equation solution in the whole simulation domain in the Gummel iteration cycles. The accuracy of this approach is investigated in comparison with the full self-consistent solution. At low drain voltage only single solution of the nonlinear Poisson equation is sufficient to extract the current with satisfactory accuracy. A pilot version of a hydrodynamic 'atomistic' simulator has been developed in order to study the effect of the nonequilibrium, non local transport in decanano MOSFETs on the random dopant induced current fluctuations. For the first time we have also applied the density gradient approach in 3D to investigate the effect of the quantum confinement on the threshold voltage fluctuations. The developed 'atomistic' simulation techniques have been applied to study various fluctuation resistant MOSFET architectures including epitaxial and delta doped devices.
Asenov, Asen↗
New Submount Requirement of Conductively Cooled Laser Diodes for Lidar Applications
New submount technology is essential for the development of conductively cooled high power diode laser. The simulation and experimental results indicate that thermal conductivity of submount for high power laser-diode must be at least 600 W/m/k or higher for stable operation. We have simulated several theoretical thermal model based on new submount designs and characterized high power diode lasers to determine temperature effects on the performances of laser diodes. The characterization system measures the beam power, output beam profile, temperature distribution, and spectroscopic property of high power diode laser. The characterization system is composed of four main parts: an infrared imaging camera, a CCD camera, a monochromator, and a power meter. Thermal characteristics of two commercial-grade CW 20-W diode laser bars with open heat-sink type were determined with respect to the line shift of emission spectra and beam power stability. The center wavelength of laser emission has a tendency to shift toward longer wavelength as the driving current and heat sink temperature are increased. The increase of heat sink temperature decreases the output power of the laser bar too. Such results lay the guidelines for the design of new submount for high power laser-diodes.
Mo, S. Y.↗