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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Performance of efficient Q-switched diode-laser-pumped Nd:YAG and Ho:YLF lasers for space applications

Solid-state lasers pumped by continuous-wave diode lasers can be Q-switched to obtain high peak power output pulses. The dependence of laser-pulse energy, average output power, peak power, and pulse width on pulse-repetition frequency in Q-switched Nd:YAG and Ho:YLF lasers is determined and compared. At low pulse repetition rates, the much longer upper-stage lifetime in Ho:YLF gives a distinct advantage. At higher pulse rates, the overall laser efficiency and the stimulated emission cross section are more important parameters, leading to an advantage for Nd:YAG. The results are of significance for designing lasers for use in space optical communications and remote sensing systems.

Marshall, W. K.↗
NASA NTRS1988

Increased effective barrier heights in Schottky diodes by molecular-beam epitaxy of CoSi2 and Ga-doped Si on Si(111)

Increasing the effective Schottky-barrier height of epitaxial CoSi2/Si(111) diodes by the use of thin, highly doped Si layers in close proximity to the metal-semiconductor interface has been studied. Intrinsic Si, Si doped by coevaporation of Ga, and epitaxial CoSi2 layers have all been grown in the same molecular-beam epitaxy system. Current-voltage and photoresponse characterization yield barrier heights ranging from 0.61 eV for a sample with no p(+) layer to 0.89 eV for a sample with a 20-nm-thick p(+) layer. These results are compared to theoretical values based on a one-dimensional solution of Poisson's equation under the depletion approximation.

Fathauer, R. W.↗
NASA NTRS1988

Fast frequency tuning and phase locking of diode-pumped Nd:YAG ring lasers

A diode-pumped single-mode monolithic Nd:YAG ring-laser oscillator has been built which can be tuned piezoelectrically over several tens of MHz in a few microsecs. Frequency stability over 1 msec is better than 500 Hz. Two lasers have been electronically phase locked for periods of minutes with a phase noise of 29 mrad rms.

Kane, Thomas J.↗
NASA NTRS1989

Tunable diode laser measurements of absolute line strengths in the 2nu2 band of N2O near 8 microns

The absolute intensities of five rotational transitions in the 2nu2 band of N2O near 8 microns have been measured with a tunable-diode laser-spectrometer. Measurements were reproducible within an average deviation of about 3 percent, and the experimental and calculated line strengths differed by only 1.5 percent. An analysis of the line strengths has yielded a band strength of S(v) = 6.98 + or - 0.26/sq cm per atm at 296 K. The band and line strengths are in excellent agreement with two recently reported values obtained by using Fourier transform-IR spectroscopy.

Tang, Lai-Wa↗
NASA NTRS1989

Tunable diode laser measurements of line widths in the nu1-fundamental band of (N-14)2(O-16) at atmospheric temperatures

A tunable diode-laser spectrometer and a low-temperature absorption cell have been employed to measure the N2-broadened and O2-broadened half-widths of rotational lines in the nu1 fundamental band of (N-14)2(O-16) at 185, 235, 263, and 295 K. The temperature dependence of the line widths has been observed to be practically identical, thereby leading to the suggestion that air-broadening would exhibit the same dependence.

Varanasi, P.↗
NASA NTRS1989

2.07-micron CW diode-laser-pumped Tm,Ho:YLiF4 room-temperature

Continuous-wave action is obtained at 2.07 microns from a 2-mm-long Tm-sensitized Ho:YLiF4 crystal at room temperature when longitudinally pumped by a pair of diode-laser arrays. Laser output power at 300 K is 26 mW, with a 30-percent slope efficiency and a lasing threshold of 108 mW. A maximum output power of 187 mW is obtained from a 4-mm-long crystal at 77 K, with a 67 percent slope efficiency. A preliminary demonstration of cavity Q switching produced 165 microJ of pulse energy at a repetition rate of 100 Hz.

Hemmati, Hamid↗
NASA NTRS1989

Phase-front measurements of an injection-locked AlGaAs laser-diode array

The phase-front quality of the primary spatial lobe emitted from an injection-locked gain-guided AlGaAs laser-diode array is measured by using an equal-path, phase-shifting Mach-Zehnder interferometer. Root-mean-square phase errors of 0.037 + or - 0.003 wave are measured for the single spatial lobe, which contained 240-mW cw output power in a single longitudinal mode. This phase-front quality corresponds to a Strehl ratio of S = 0.947, which results in a 0.23-dB power loss from the single lobe's ideal diffraction-limited power. These values are comparable with those measured for single-stripe index-guided AlGaAs lasers.

Cornwell, Donald M., Jr.↗
NASA NTRS1989

Frequency fluctuations of a diode-pumped Nd:YAG ring laser

The spectral density of the frequency fluctuations of a diode-pumped single-mode monolithic Nd:YAG ring laser was measured by locking a Fabry-Perot resonator to the laser frequency. The fluctuations approach the limit due to spontaneous emission (the Schawlow-Townes limit) at frequencies above 80 kHz. The inherent frequency stability of these lasers makes them attractive as a potential light source for gravitational-wave interferometers.

Fritschel, Peter↗
NASA NTRS1989

Frequency stability of a tunable diode laser mounted in a compact Stirling cycle cooler

A tunable diode laser (TDL) has been operated with a compact lightweight closed-cycle Stirling cooler. The laser linewidth has been measured near 80 K and found to be about half of that when using more massive closed-cycle coolers. Novel applications include balloon-borne and aircraft-adapted instruments, where size, weight, and power requirements place stringent demands on necessary TDL cooling systems.

Durso, Santo S.↗
NASA NTRS1990

Self-Aligned Guard Rings For Schottky-Barrier Diodes

Proposed self-aligned guard ring increases active area of Schottky-barrier infrared detector. Concept developed for silicide Schottky-barrier diodes in which platinum silicide or iridium silicide Schottky-contacts provide cutoff wavelengths of about 6 or 10 micrometers. Grid of silicon dioxide doped with phosphorus etched on silicon wafer, and phosphorus from grid diffused into substrate, creating n-type guard rings. Silicide layers formed in open areas of grid. Overlap of guard rings and silicide layers small.

Lin, True-Lon↗
NASA NTRS1989

Optical communication with semiconductor laser diode

This interim report describes the progress in the construction of a 220 Mbps Q=4 PPM optical communication system that uses a semiconductor laser as the optical transmitter and an avalanche photodiode (APD) as the photodetector. The transmitter electronics have been completed and contain both GaAs and ECL III IC's. The circuit was able to operate at a source binary data rate from 75 Mbps to 290 Mbps with pulse rise and fall times of 400 ps. The pulse shapes of the laser diode and the response from the APD/preamplifier module were also measured.

Davidson, Frederic↗
NASA NTRS1990

Direct detection optical intersatellite link at 220 Mbps using AlGaAs laser diode and silicon APD with 4-ary PPM signaling

A newly developed 220 Mbps free-space 4-ary pulse position modulation (PPM) direct detection optical communication system is described. High speed GaAs integrated circuits were used to construct the PPM encoder and receiver electronic circuits. Both PPM slot and word timing recovery were provided in the PPM receiver. The optical transmitter consisted of an AlGaAs laser diode (Mitsubishi ML5702A, lambda=821nm) and a high speed driver unit. The photodetector consisted of a silicon avalanche photodiode (APD) (RCA30902S) preceded by an optical interference filter (delta lambda=10nm). Preliminary tests showed that the self-synchronized PPM receiver could achieve a receiver bit error rate of less than 10(exp -6) at 25 nW average received optical signal power or 360 photons per transmitted information bit. The relatively poor receiver sensitivity was believed to be caused by the insufficient electronic bandwidth of the APD preamplifier and the poor linearity of the preamplifier high frequency response.

Sun, Xiaoli↗
NASA NTRS1989

A modified equivalent-width technique for diode-laser line strength measurements

A modified equivalent-width method is introduced that improves the accuracy of spectral line strength measurements using diode lasers. This method differs from the standard method in that no attempt is made to calculate the true equivalent width in order to determine the line strength. Instead, the line strength is derived directly from a measurement of the area under the line close to the line center and ignore the normal correction terms. Tests with actual spectra and simulations indicate that this method is accurate to better than 1 percent with lines broadened by up to 50 percent by the laser instrument function.

Strow, L. Larrabee↗
NASA NTRS1990

Active frequency stabilization of a 1.062-micron, Nd:GGG, diode-laser-pumped nonplanar ring oscillator to less than 3 Hz of relative linewidth

Results are presented on the frequency stabilization of two diode-laser-pumped ring lasers that are independently locked to the same high-finesse interferometer. The relative frequency stability is measured by locking the lasers one free spectral range apart and observing the heterodyne beat note. The resultant beat note width of 2.9 Hz is consistent with the theoretical system noise-limited linewidth and is approximately 20 times that expected for shot-noise-limited performance.

Day, T.↗
NASA NTRS1989

Optomechanical design considerations in the development of the DDLT laser diode collimator

A laser diode collimator objective was developed in support of the Direct Detection Transceiver program. Close attention to optomechanical design issues including athermalization, alignment, selection of materials, mounting of elements, and hermetic sealing of the assembly was necessary to insure that the desired optical performance was maintained in space deployment.

Kampe, Thomas U.↗
NASA NTRS1990

Heterodyne spectrophotometry of ozone in the 9.6-micron band using a tunable diode laser

Tunable diode laser heterodyne spectrophotometry (TDLHS) has been used to make extremely high resolution (0.0003/cm) solar spectra in the 9.6-micron ozone band. Observations have shown that a signal-to-noise ratio of 120:1 (about 30 percent of theoretical) for an integration time of 1/8 s can be achieved at a resolution of 0.0013 wave numbers. The spectral data have been inverted to yield a total column amount of ozone, in good agreement with that measured at the nearby NOAA ozone monitoring facility in Boulder, Colorado. Line positions for several ozone lines in the spectral region 996-997/cm are reported. Recent improvements have produced a signal-to-noise ratio of 95:1 (about 40 percent of theoretical) at 0.0003/cm and extended the range of wavelengths which can be observed.

Mcelroy, C. T.↗
NASA NTRS1990

Intensity noise in diode-pumped single-frequency Nd:YAG lasers and its control by electronic feedback

The power spectrum of the relative intensity noise (RIN) of single-frequency diode-pumped Nd:YAG lasers is observed to be shot-noise limited at frequencies above 20 MHz for a photocurrent of up to 4.4 mA. Relaxation oscillations result in noise 60-70 dB above shot noise at a few hundred kHz. These relaxation oscillations have been suppressed using electronic feedback.

Kane, Thomas J.↗
NASA NTRS1990

Efficiency of Nd laser materials with laser diode pumping

For pulsed laser-diode-pumped lasers, where efficiency is the most important issue, the choice of the Nd laser material makes a significant difference. The absorption efficiency, storage efficiency, and extraction efficiency for Nd:YAG, Nd:YLF, Nd:GSGG, Nd:BEL, Nd:YVO4, and Nd:glass are calculated. The materials are then compared under the assumption of equal quantum efficiency and damage threshold. Nd:YLF is found to be the best candidate for the application discussed here.

Barnes, Norman P.↗