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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

A variable-data-rate, multimode quadriphase modem.

This paper describes the design and performance of a highly versatile modulator and demodulator recently developed to facilitate the evaluation of various digital communications links. The modem is capable of either PSK or QPSK operation and can accommodate a very wide range of continuously tunable data rates (1 kbps to 30 Mbps in each of two channels). In the QPSK mode, operation is possible using either a single serial data stream (single channel operation) or using two mutually independent, unrelated, and asynchronous data streams (dual-channel operation). Integrate and dump detectors are used at the demodulator for regeneration of the data stream(s). Measurements indicate that the performance of the overall system (including the bit detectors) is within 2 dB of the theoretically optimum performance of either PSK or QPSK at any rate within the range of rates provided by the modem, and is within 1 dB of theoretical over most of the range of rates.

Allen, R. W.↗
NASA NTRS1973

Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation

Work continued on a number of projects aimed at the generation of tunable visible, infrared, and ultraviolet light; and on the control of this light by means of novel mode-locking and modulation techniques. Progress is summarized for the following projects: (1) the transient modelocking of the Nd:YAG laser and application of short optical pulses; (2) studies of the sodium-xenon excimer laser; (3) development of techniques for vacuum ultraviolet holography; and (4) studies of multiple photon pumped xenon and argon excimer lasers.

Harris, S. E.↗
NASA NTRS1973

Optical and infrared masers

Ongoing research progress in the following areas is described: (1) tunable infrared light sources and applications; (2) precision frequency and wavelength measurements in the infrared with applications to atomic clocks; (3) zero-degree pulse propagation in resonant medium; (4) observation of Dicke superradiance in optically pumped HF gas; (5) unidirectional laser amplifier with built-in isolator; and (6) progress in infrared metal-to-metal point contact tunneling diodes.

Source record↗
NASA NTRS1973

Recent progress in the hydrographic applications of a N2/Ne laser

Laboratory and field measurements have been performed on the transmission/scattering characteristics of a pulsed neon laser as a function of water turbidity. These results have been used to establish the criteria for an airborne laser bathymetry system. Extensive measurements have been made of laser induced fluorescence using a pulsed tunable dye laser. Feasibility has been demonstrated for remote detection and possible identification of various types of algae and oils. Similar measurements made on a wide variety of organic dyes have shown this technique to have applications in remote measurement of subsurface currents, temperature, and salinity.

Hickman, G. D.↗
NASA NTRS1975

Communications and navigation

The use of a computer simulation to quantitatively measure the distortion on a standard video test signal which experiences frequency modulation, filtering, and frequency demodulation is discussed. The process is applied to frequency modulated television systems for use with the ATS-F spacecraft. A block diagram of the system is presented. The characteristics of a millimeter wave space communication system are analyzed. The application of the Omega position location equipment (OPLE) for a global rescue net is reported. The development of a high speed photodetector for the neodynium yag laser system is discussed and the characteristics of the system are explained. The effects of gas pressure on waveguide laser tunability are examined.

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NASA NTRS1975

Planetary investigation utilizing an imaging spectrometer system based upon charge injection technology

An intrinsic silicon charge injection device (CID) television sensor array has been used in conjunction with a CaMoO4 colinear tunable acousto optic filter, a 61 inch reflector, a sophisticated computer system, and a digital color TV scan converter/computer to produce near IR images of Saturn and Jupiter with 10A spectral resolution and approximately 3 inch spatial resolution. The CID camera has successfully obtained digitized 100 x 100 array images with 5 minutes of exposure time, and slow-scanned readout to a computer. Details of the equipment setup, innovations, problems, experience, data and final equipment performance limits are given.

Wattson, R. B.↗
NASA NTRS1975

Recent advances in the applications of pulsed lasers in the hydrosphere

Laboratory and field measurements have been performed on the transmission/scattering characteristics of a pulsed neon laser as a function of water turbidity. These results have been used to establish the criteria for an airborne laser bathymetry system. Extensive measurements have been made of laser induced fluorescence using a pulsed tunable dye laser. Feasibility has been demonstrated for remote detection and possible identification of various types of algae and oils. Similar measurements made on a wide variety of organic dyes have shown this technique to have applications in remote measurements of subsurface currents, temperature and salinity.

Hickman, G. D.↗
NASA NTRS1975

Sensitivity limits of an infrared heterodyne spectrometer for astrophysical applications

A discussion and an evaluation of the degradation in sensitivity is given for a heterodyne spectrometer employing a HgCdTe photodiode mixer and tunable diode lasers. The minimum detectable source brightness is considered as a function of the mixer parameters, transmission coefficient of the beam splitter, and local oscillator emission powers. The degradation in the minimum detectable line source brightness which results from the bandwidth being a function of the line width is evaluated and plotted as a function of the wavelength and bandwidth for various temperature to mass ratios. It is shown that the minimum achievable degradation in the sensitivity of a practical astronomical heterodyne spectrometer is approximately 30. Estimates of signal-to-noise ratios with which infrared line emission from astronomical sources of interest may be detected are given.

Abbas, M. M.↗
NASA NTRS1974

A 1.4-4-micron high-energy angle-tuned LiNbO3 parametric oscillator

The performance characteristics of a widely tunable infrared source that can be rapidly and conveniently angle tuned over the entire 1.4-4.4 micron range are reported. It is significant that the source requires only one set of optics and a single LiNbO3 crystal to tune the entire range. Conversion efficiencies of 15% and an operating amplitude stability of better than 3% have been demonstrated. The availability of large 15-mm-diam by 5-cm-long 47-deg cut LiNbO3 crystals makes possible oscillator operation at up to 2 J of 1.06-micron input pulse energy.

Herbst, R. L.↗
NASA NTRS1975

Stimulated Stokes emission with a dye laser - Intense tuneable radiation in the infrared

Tunable stimulated Stokes emission is generated at approximately 2.9 microns in barium vapor with an oscillator-amplifier dye laser. The conversion efficiency is as high as 40% and the energy output as high as 30 mJ. The emission is tuneable over about 100 wavenumbers. At high vapor pressures the tuning profile is markedly asymmetric.

Carlsten, J. L.↗
NASA NTRS1975

Source self-mixing in the detection of extended incoherent sources

We consider the self-beating of incoherent light from an extended source at a wideband photomixer. The intermediate frequency mean squared current is found to be proportional to the product of the direct detected source power and the power within the IF bandpass about the optical frequency and within the heterodyne field of view. Thus the ratio of the heterodyne signal to self-beating power is proportional to the ratio of local oscillator power to direct detected power. This ratio is usually large for systems employing efficient local oscillators that generate shot-noise-limited operation. In less efficient systems, such as those employing tunable diode lasers, the effects of self-mixing may be significant.

Cohen, S. C.↗
NASA NTRS1975

Effects of focusing on third-order nonlinear processes in isotropic media

Third-order nonlinear processes in isotropic media have been successfully used for tripling the efficiency of high-power laser radiation for the production of tunable and fixed-frequency coherent vacuum UV radiation and for up-conversion of IR radiation. The effects of focusing on two processes of this type are studied theoretically and experimentally.

Bjorklund, G. C.↗
NASA NTRS1975

Resonant Doppler velocimeter

Narrow linewidth tunable lasers augur a new kind of laser Doppler velocimetry employing resonant absorption and fluorescence from trace atomic species rather than scattering from particles. This technique may provide better turbulence and small volume information than present velocimetry.

Miles, R. B.↗
NASA NTRS1975

An infrared heterodyne radiometer for high-resolution measurements of solar radiation and atmospheric transmission

A tunable, Dicke-switched, infrared heterodyne radiometer (IHR) has been designed, fabricated, tested, and used to observe solar radiation and determine the atmospheric transmissivity in the 9-11-micron spectral band. The IHR provides a spectral resolution of 0.0067 reciprocal cm, a minimum detectable power level of 2.9 times ten to the minus twenty-third power W/Hz, and a temperature resolution of less than 1 K for a source temperature of 1000 K, an IF predetection bandwidth of 100 MHz, and an integration time of 30 s. Detailed design equations and measured IHR performance are presented. The IHR was used to make solar and atmospheric transmission measurements, and a vertical-path atmospheric attenuation of 2.3 dB has been established under favorable weather conditions. The attenuation of solar radiation due to cloud cover and haze has also been investigated.

Peyton, B. J.↗
NASA NTRS1976

Water vapor lidar

The feasibility was studied of measuring atmospheric water vapor by means of a tunable lidar operated from the space shuttle. The specific method evaluated was differential absorption, a two-color method in which the atmospheric path of interest is traversed by two laser pulses. Results are reported.

Ellingson, R.↗
NASA NTRS1976

Exploratory laser experiments

Experiments are described which were undertaken to explore the application of various dye laser methods for generating laser pulses which could be tuned over H2O absorption lines in the visible and near infrared. Specific topics discussed include: operation of a long pulse dye laser with a tunable, narrow band output at high energies near the 5915 A water vapor absorption bands; assembly and operation of a short duration dye laser near the 5915 A water vapor absorption bands; construction of a dye laser to be pumped to operate in the red and near infrared; and preliminary studies of the beam divergence of the output of the a laser-pumped system. Results are summarized.

Source record↗
NASA NTRS1976

Sensitivity limits of an infrared heterodyne spectrometer for astrophysical applications

A discussion and an evaluation of the degradation in sensitivity are given for a heterodyne spectrometer employing a HgCdTe photodiode mixer and tunable diode lasers. The minimum detectable source brightness is considered as a function of the mixer parameters, transmission coefficient of the beam splitter, and local oscillator emission powers. The degradation in the minimum detectable line source brightness that results from the bandwidth being a fraction of the line width is evaluated and plotted as a function of the wavelength and bandwidth for various temperature to mass ratios. It is shown that the minimum achievable degradation in the sensitivity of a practical astronomical heterodyne spectrometer is about 30. Estimates of SNRs with which IR line emission from astronomical sources of interest may be detected are given.

Abbas, M. M.↗