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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

High resolution atmospheric spectroscopy using a diode laser heterodyne spectrometer

Ultrahigh resolution (0.007 per cm) atmospheric solar absorption spectra that have been obtained from a tunable infrared heterodyne radiometer are discussed. The radiometer was developed for ground based observations in the 8-12 micron region, and tunability is achieved through the use of Pb-salt semiconductor laser local oscillators. Spectra have been obtained in a piecewise fashion from 9.1 to 11.1 microns using laser emission modes that exhibit characteristics suitable for local-oscillator operation. Spectra showing absorption features of HNO3, O3, CO2, and H2O are presented along with comparisons of experimental and synthetic spectra calculated using a line-by-line atmospheric transmission model.

Hoell, J. M., Jr.↗
NASA NTRS1982

Terraced-heterostructure large-optical-cavity AlGaAs diode laser - A new type of high-power CW single-mode device

A new terraced lateral wave confining structure is obtained by liquid phase epitaxy over channeled substrates misoriented perpendicular to the channels' direction. Single spatial and longitudinal mode CW operation is achieved to 50 mW from one facet, in large spot sizes (2 x 7.5 micron, 1/e squared points in intensity) and narrow beams (6 deg x 23 deg), full width half-power). At 70 C ambient temperature CW lasing is obtained to 15 mW from one facet. Weak mode confinement in an asymmetric lateral waveguides provides discrimination against high-order mode oscillation.

Botez, D.↗
NASA NTRS1983

Electrolytic Sharpening of Diode-Contact Whiskers

Phosphor bronze wire pointed without highly-toxic chemical reagents. Phosphor bronze wire to be pointed affixed to metal post held by fixture, such as pin vise. Fixture moved axially by micrometer allows precise control of position of end of wire with respect to surface of pointing solution. Solution consists of 4 weight percent sulfamic acid crystals in deionized water. Dissolution current adjusted via the autotransformer setting.

Green, G.↗
NASA NTRS1984

Low-Noise Submillimeter-Wave Diode

Low noise achieved without usual high resistance. Barrier of p-type material placed between metal anode and heavily-doped gallium arsenide. Ntype epitaxial layer eliminated. Barrier prevents quantum tunneling of electrons between semiconductor and metal. Higher breakdown structure provided.

Mattauch, R. J.↗
NASA NTRS1982

Holograms for laser diode: Single mode optical fiber coupling

The low coupling efficiency of semiconductor laser emissions into a single mode optical fibers place a severe restriction on their use. Associated with these conventional optical coupling techniques are stringent alignment sensitivities. Using holographic elements, the coupling efficiency may be increased and the alignment sensitivity greatly reduced. Both conventional and computer methods used in the generation of the holographic couplers are described and diagrammed. The reconstruction geometries used are shown to be somewhat restrictive but substantially less rigid than their conventional optical counterparts. Single and double hologram techniques are examined concerning their respective ease of fabrication and relative merits.

Fuhr, P. L.↗
NASA NTRS1984

Optical communication with laser diode arrays

The performance of a direct-detection optical communication system in which the laser transmitter sends short optical pulses of selected nonoverlapping center frequencies is analysed. This modulation format, in which a single light pulse is sent in one of M time slots at one of N optical center frequencies, is referred to as color coded optical pulse position modulation (CCPPM). The optimum energy-efficiency of this system, as measured by the channel capacity in nats per photon, exceeds that of ordinary optical pulse position modulation which uses a pulsed laser of fixed optical frequency. Reliable communication at optimal energy efficiency is easily achieved through the use of modest block length Reed-Solomon codes with the code words represented as CCPPM symbols.

Davidson, F.↗
NASA NTRS1984

Lead salt diode lasers and development of tunable solid state lasers for remote sensing

Extensive studies of the output characteristics of single quantum well lead-telluride lasers developed at the General Motors Research Laboratories were carried out. Threshold currents, output powers and line structures were measured as a function of temperature. Very low-current lasing thresholds, record high operating temperatures and over 30% tuning ranges were achieved. Excellent reproducibilities, good far-field patterns and reasonable linewidths (approx. 500 kHz) were found.

Freed, C.↗
NASA NTRS1983

Automated control and data acquisition for a tunable diode laser heterodyne spectrometer

This paper describes the hardware and software design, development, and implementation of the control and data electronics of a laser heterodyne spectrometer instrument being built at NASA Langley Research Center for a technology demonstration. Functional partitioning, applied at all levels of hardware and software, has been found to provide expedient design, development, and testing of the instrument. The instrument is composed of distributed microprocessor-based units. A master/slave protocol is presented which can be simulated by a terminal for unit checkout. All but one of the units are implemented using a set of core boards, plus unique boards where necessary. This design has led to reduced hardware development, reduced parts inventory, and replication of software modules, while providing the flexibility needed for a development instrument. The development tools and documentation guidelines are discussed.

Shull, T. S.↗
NASA NTRS1983

Heterodyne frequency measurements and frequency calibration standards for tunable diode lasers

New frequency calibration tables are required to keep abreast of the resolution attainable by currently available tunable lasers. One key to the generation of tables with requisite accuracy involves accurate heterodyne frequency measurements; another key consists of reliable fitting and analysis. Coordinated activity in NBS involves selection of suitable molecular calibration candidates, their frequency measurement and analysis, and dissemination of the results in the form of frequency calibration tables. Current status of these efforts is described.

Wells, J. S.↗
NASA NTRS1984

Controlled fundamental supermode operation of phase-locked arrays of gain-guided diode lasers

Uniform semiconductor laser arrays tend to oscillate in a superposition of their supermodes, thus leading to large beam divergence and spectral spread. Discrimination among the supermodes in phase-locked arrays is discussed theoretically. It is shown that supermode discrimination in gain-guided arrays, in favor of the fundamental supermode, is made possible by the near-field interference patterns which result from the complex optical fields of the gain-guided lasers. A fundamental supermode operation is demonstrated, for the first time, in GaAlAs/GaAs gain-guided laser arrays. This is achieved by control of the current (gain) profile across the array by means of individual laser contacts.

Kapon, E.↗
NASA NTRS1985

Damping Relaxation Oscillations in Laser Diodes

Proposed semiconductor laser modulated at frequencies up to near its resonant frequency more efficiently than older devices. New laser uses two different effective carrier lifetimes: one for dc and lowfrequency operation and another for operation near resonant frequency. Laser part of bipolar transistor with capacitor that serves as ac short circuit.

Katz, J.↗
NASA NTRS1985

Measurements of vector fields with diode array

A polarimeter was designed for high spatial and spectral resolution. It consists of a quarter-wave plate alternately operating in two positions for Stoke-V measurements and an additional quarter-wave plate for Stokes-U and -Q measurements. The spatial range covers 75 arcsec, the spectral window of about 1.8 a allows the simultaneous observations of neighboring lines. The block diagram of the data processing and acquisition system consists of five memories each one having a capacity of 10 to the 4th power 16-bit words. The total time to acquire profiles of Stokes parameters can be chosen by selecting the number of successive measurements added in the memories, each individual measurement corresponding to an integration time of 0.5 sec. Typical values range between 2 and 60 sec depending on the brightness of the structure, the amount of polarization and a compromise between desired signal-to-noise ratio and spatial resolution.

Wiehr, E. J.↗
NASA NTRS1984

Space-charge behavior of 'Thin-MOS' diodes with MBE-grown silicon films

Basic theoretical and experimental characteristics of a novel 'Thin-MOS' technology, which has promising aspects for integrated high-frequency devices up to several hundred gigahertz are presented. The operation of such devices depends on charge injection into undoped silicon layers of about 1000-A thickness, grown by molecular beam epitaxy on heavily doped substrates, and isolation by thermally grown oxides of about 100-A thickness. Capacitance-voltage characteristics measured at high and low frequencies agree well with theoretical ones derived from uni and ambipolar space-charge models. It is concluded that after oxidation the residual doping in the epilayer is less than approximately 10 to the 16th/cu cm and rises by 3 orders of magnitude at the substrate interface within less than 100 A and that interface states at the oxide interface can be kept low.

Lieneweg, U.↗
NASA NTRS1985

Coupled-mode analysis of gain and wavelength oscillation characteristics of diode laser phased arrays

The lasing wavelengths and gain characteristics of the modes of phase-locked arrays of channel-substrate-planar (CSP) lasers are presented. The gain values for the array modes are determined from complex coupling coefficients calculated using the fields of neighboring elements of the array. The computations show that, for index guided lasers which have nearly planar phase fronts, the highest order array mode will be preferred. The 'in-phase' or fundamental mode, which produces only one major lobe in the far-field radiation pattern, has the lowest modal gain of all array modes. The modal gain differential between the highest order and fundamental modes is less than 10/cm for weak coupling between the elements.

Butler, J. K.↗