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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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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The 1.1 micrometer and visible emission semiconductor diode lasers

In (AlGa)As, the first of three alloy systems studied, Continuous Wave (CW) operation was obtained at room temperature at a wavelength as low as 7260 A. Reliability in this system was studied in the incoherent mode. Zinc doped devices had significant degradation, whereas Ge or Ge plus Zi doped devices had none. The Al2O3 facet coatings were shown to significantly reduce facet deterioration in all types of lasers, longer wavelength units of that type having accumulated (at the time of writing) 22,000 hours with little if any degradation. A CL study of thin (AlGa)As layers revealed micro fluctuation in composition. A macro-scale fluctuation was observed by electroreflectance. An experimental and theoretical study of the effect of stripe width on the threshold current was carried out. Emission below 7000 A was obtained in VPE grown Ga(AsP) (In,Ga)P with CW operation at 10 C. Lasers and LED's were made by LPE in (InGa) (AsP). Laser thresholds of 5 kA/cm2 were obtained, while LED efficiences were on the order of 2%. Incoherent life test over 6000 hours showed no degradation.

Ladany, I.↗
NASA NTRS1980

Far-field radiation pattern of tunable diode lasers

Technique rapidly determines far-field spatial energy distribution. Method takes about 3 minutes. It is optically simple and is economical, using standard laboratory parts and equipment. It records automatically without operator control and is easily adaptable to computer control of input instructions and computer treatment of output data. Degree of data resolution is limted only by width of recorder pen, and data are repeatable.

Lash, T. J.↗
NASA NTRS1980

Advances in tunable diode laser technology

The improvement of long-term reliability, the purification of mode properties, and the achievement of higher-temperature operation were examined. In reliability studies a slow increase in contact resistance during room temperature storage for lasers fabricated with In-Au or In-Pt contacts was observed. This increase is actually caused by the diffusion of In into the surface layer of laser crystals. By using a three layered structure of In-Au-Pt or In-Pt-Au, this mode of degradation was reduced. In characterizing the mode properties, it was found that the lasers emit in a highly localized, filamentary manner. For widestripe lasers the emission occurs near the corners of the junction. In order to achieve single-mode operation, stripe widths on the order of 8-10 micrometers are needed. Also, it was found that room temperature electroluminescence is possible near 4.6 micrometers.

Lo, W.↗
NASA NTRS1982

Line intensities from band and diode laser measurements: Neutrino 4 of CH4

The experimental data and theoretical work on the 7.7 micron band of methane are reviewed. This band is particularly relevant in studies of the atmospheres of Jupiter, Saturn and the other outer planets. Methane spectra taken from the infrared spectrometer (IRIS) aboard Voyager, and a temperature profile derived by inverting those data, both for hydrogen and methane are presented.

Fox, K.↗
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 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

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.↗