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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Pulse compression inside an actively AM mode-locked Nd:YAG laser using a liquid Kerr cell

A mode-locked Nd:YAG laser capable of generating pulses substantially shorter than the present limit of 30-50 ps, while retaining the stability of active mode locking, would be a useful development. This study presents a simplified theoretical analysis and a preliminary experimental verification of the use of an optical Kerr cell as a passive lossless pulse compressor inside a Q-switched and actively mode-locked YAG laser. The theoretical model indicates possible compression to as short as about 5 ps in a typical low-power Nd:YAG laser. The preliminary experimental results show substantial pulse compression via the predicted mechanism, though still not below about 30 ps. The technique appears capable, however, of pulse compression to substantially shorter values without the instabilities, statistical fluctuations, or energy losses associated with saturable-absorber mode locking.

Duerinckx, A. J.↗
NASA NTRS1980

Episodic mantle differentiation - Nd and Sr isotopic evidence

A study of Nd and Sr isotopic composition of clinopyroxenes separated from two hydrous and four anhydrous ultramafic nodules is presented. Correlation of Nd-143/Nd-144 with Sm/Nd suggests that a second partial melting occurred about 560 m.y. ago resulting in LREE enrichment of a part of the anhydrous mantle. The isotopic data for anhydrous nodules show that oceanic type mantle underlies at some continental areas. It is concluded that the separation of subcontinental mantle regions from an initially chondritic reservoir may occur in discrete episodes, and that different histories of depletion and/or enrichment will produce isotopically distinct mantle reservoirs.

Stosch, H. G.↗
NASA NTRS1970

The Nd-Rh system

Phase diagram of Nd-Rh system determined by powder X ray diffraction, metallography and differential thermal analysis methods

Raman, A.↗
NASA NTRS1971

Space qualified Nd:YAG laser (phase 1 - design)

Results of a design study and preliminary design of a space qualified Nd:YAG laser are presented. A theoretical model of the laser was developed to allow the evaluation of the effects of various parameters on its performance. Various pump lamps were evaluated and sum pumping was considered. Cooling requirements were examined and cooling methods such as radiation, cryogenic and conductive were analysed. Power outputs and efficiences of various configurations and the pump and laser lifetime are discussed. Also considered were modulation and modulating methods.

Foster, J. D.↗
NASA NTRS1973

LED pumped Nd:YAG laser development program

The results of a development program for light emitting diode (LED) pumped Nd:YAG lasers are described. An index matching method to increase the coupling efficiency of the laser is described. A solid glass half-cylinder of 5.0 by 5.6 centimeters was used for index matching and also as a pumping cavity reflector. The laser rods were 1.5 by 56 millimeters with dielectric coatings on both end surfaces. The interfaces between the diode array, glass cylinder, and laser rod were filled with viscous fluid of refractive index n = 1.55. Experiments performed with both the glass cylinder and a gold coated stainless steel reflector of the same dimensions under the same operating conditions indicate that the index matching cylinder gave 159 to 200 percent improvement of coupling efficiency over the metal reflector at various operating temperatures.

Farmer, G. I.↗
NASA NTRS1973

Simultaneous Q-switching and mode-locking in the CW Nd:YAG laser

The theory of transient mode-locking for an active modulator in a laser with a homogeneously broadened line is presented. The theory is applied to simultaneously Q-switched and mode-locked Nd:YAG lasers and good agreement between theory and experiment is obtained. The main conclusion is that under usual Q-switched operating conditions the mode-locking process does not have sufficient time to build up to steady-state conditions. We also present a method to overcome this problem by allowing the laser to prelase before the Q-switch is opened. Mode-locked pulses whose width approaches the steady-state value are obtained. The transient mode-locking theory presented here also applies to actively mode-locking TEA CO2 lasers and to other types of simultaneously pulsed and mode-locked lasers.

Kuizenga, D. J.↗
NASA NTRS1976

Diode pumped Nd:YAG laser development

A low power Nd:YAG laser was constructed which employs GaAs injection lasers as a pump source. Power outputs of 125 mW TEM CW with the rod at 250 K and the pump at 180 K were achieved for 45 W input power to the pump source. Operation of the laser, with array and laser at a common heat sink temperature of 250 K, was inhibited by difficulties in constructing long-life GaAs LOC laser arrays. Tests verified pumping with output power of 20 to 30 mW with rod and pump at 250 K. Although life tests with single LOC GaAs diodes were somewhat encouraging (with single diodes operating as long as 9000 hours without degradation), failures of single diodes in arrays continue to occur, and 50 percent power is lost in a few hundred hours at 1 percent duty factor. Because of the large recent advances in the state of the art of CW room temperature AlGaAs diodes, their demonstrated lifetimes of greater than 5,000 hours, and their inherent advantages for this task, it is recommended that these sources be used for further CW YAG injection laser pumping work.

Reno, C. W.↗
NASA NTRS1977

Length controlled stabilized mode-lock ND:YAG laser

A method and apparatus for stabilizing the amplitude and repetition rate of mode-locked Nd:YAG laser pulses by controlling the laser length through a feedback loop are described. The end mirror of the laser is mounted on a piezoelectric crystal which is dithered at a low frequency. A portion of fundamental 1.06 micrometer laser radiation is converted into its second harmonic frequency, and the average power of the second harmonic frequency is detected by an integrating detector. The amount of the power of the second harmonic frequency depends on the match between the optical length of the laser cavity and the mode-lock frequency. The length is controlled by a feedback loop which phase compares the output of the second harmonic detector to the piezoelectric crystal dither signal.

Sigfred, J.↗
NASA NTRS1976

Mode-locked frequency doubled Nd:YAG laser

The design, fabrication, test, and delivery of two mode-locked, frequency doubled Nd:YAG laser systems are described. Each system was comprised of two units, the laser head and optics on an Invar plate and the electronics control unit in a relay rack chassis panel. Laser number one operated at a repetition rate of 400 MHz and was designed for use in an optical communication system. Laser number two operated at 200 MHz repetition rate and was designed for optical ranging and target signature experiments. Both lasers had a pulse width of 200 ps at the 10% amplitude points at 1.064 micrometer wavelength (150 ps at 0.532 micrometers) with an amplitude stability of + or - 4%. Output power exceeded the design goals.

Brookman, J. S.↗
NASA NTRS1979

The Sr and Nd isotopic record of Apollo 12 basalts - Implications for lunar geochemical evolution

Alkali, alkaline earth, and rare earth element data are reported for several Apollo 12 basalts which are representative of the four Apollo 12 magma types. Results confirm the heterogeneity of the lunar mantle and show that the Sm/Nd ratio of at least the Apollo 12 ilmenite basalts was decreased by 13-24% during magma genesis. In addition, whole mare basalt Sm-Nd data are not collinear on an isochron diagram; thus it is no longer possible to explain these data via mixing of 'primitive material' and 'early differentiates' as in the hybridization and assimilation models.

Nyquist, L. E.↗
NASA NTRS1980

Analysis of mode-locked and intracavity frequency-doubled Nd:YAG laser

The paper presents analytical and computer studies of the CW mode-locked and intracavity frequency-doubled Nd:YAG laser which provide new insight into the operation, including the detuning behavior, of this type of laser. Computer solutions show that the steady-state pulse shape for this laser is much closer to a truncated cosine than to a Gaussian; there is little spectral broadening for on-resonance operation; and the chirp is negligible. This leads to a simplified analytical model carried out entirely in the time domain, with atomic linewidth effects ignored. Simple analytical results for on-resonance pulse shape, pulse width, signal intensity, and harmonic conversion efficiency in terms of basic laser parameters are derived from this model. A simplified physical description of the detuning behavior is also developed. Agreement is found with experimental studies showing that the pulsewidth decreases as the modulation frequency is detuned off resonance; the harmonic power output initially increases and then decreases; and the pulse shape develops a sharp-edged asymmetry of opposite sense for opposite signs of detuning.

Siegman, A. E.↗