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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Optimized Biasing of Pump Laser Diodes in a Highly Reliable Metrology Source for Long-Duration Space Missions

Non Planar Ring Oscillator (NPRO) lasers are highly attractive for metrology applications. NPRO reliability for prolonged space missions is limited by reliability of 808 nm pump diodes. Combined laser farm aging parameter allows comparing different bias approaches. Monte-Carlo software developed to calculate the reliability of laser pump architecture, perform parameter sensitivity studies To meet stringent Space Interferometry Mission (SIM) Lite lifetime reliability / output power requirements, we developed a single-mode Laser Pump Module architecture that: (1) provides 2 W of power at 808 nm with >99.7% reliability for 5.5 years (2) consists of 37 de-rated diode lasers operating at -5C, with outputs combined in a very low loss 37x1 all-fiber coupler

laser communications↗
NASA NTRS1983

Airborne tunable diode laser system for trace gas measurements

Sachse et al. (1976) have reported the development of an airborne tunable diode laser (TDL) system, named the Differential Absorption CO Monitor (DACOM). The absorption path was 10 m long and located in the free airstream along the fuselage of a C-54 aircraft. The present investigation is concerned with a modification of the DACOM instrument. Differences between the new instrument and the original one are related to a replacement of the external absorption path with a White cell. The instrument has the capability to suppress TDL excess noise. The laser refrigerator has been redesigned to permit an alternative method of cooling the TDL when electric power is not available.

Sachse, G. W.↗
NASA NTRS1991

Airborne tunable diode laser sensor for high-precision concentration and flux measurements of carbon monoxide and methane

An airborne tunable diode laser instrument is described that is capable of operating in two measurement modes. One mode provides high precision (0.1 percent CH4; 1 percent CO) measurements of CH4 and CO with a 5 second response time, and a second mode achieves the very fast response time that is necessary to make airborne eddy correlation flux measurements. Examples of data from atmospheric expeditions of the Global Tropospheric Experiment are presented.

Sachse, G. W.↗
NASA NTRS1991

Gaseous oxygen detection using laser diodes

Transitions in the R-branch of the O2 A-band have been observed by modulating IR laser diode temperatures; on the basis of these transitions, O2 concentrations as low as 750 ppm can be determined. The transmission measurement's achievable precision correlates with an O2 concentration uncertainty of only 0.5 percent. Both the concentration and the static temperature of the gas are thereby determinable. Improved optics are being designed to improve these performance figures.

Fox, Curtis W.↗
NASA NTRS1980

New PbSnTe heterojunction laser diode structures with improved performance

Several recent advances in the state-of-the-art of lead tin telluride double heterojunction laser diodes are summarized. Continuous Wave operation to 120 K and pulsed operation to 166 K with single, lowest order transverse mode emission to in excess of four times threshold at 80 K were achieved in buried stripe lasers fabricated by liquid phase epitaxy in the lattice-matched system, lead-tin telluride-lead telluride selenide. At the same time, liquid phase epitaxy was used to produce PbSnTe distributed feedback lasers with much broader continuous single mode tuning ranges than are available from Fabry-Perot lasers. The physics and philosophy behind these advances is as important as the structures and performance of the specific devices embodying the advances, particularly since structures are continually being evolved and the performance continues to be improved.

Fonstad, C. G.↗
NASA NTRS1979

Tunable diode laser measurements of line strengths in the nu4 band of C-12H4

Absolute intensities have been measured, using a diode laser spectrometer for several vibration-rotation lines in the nu4 fundamental of methane. The data have been analyzed, with the inclusion of Coriolis interactions, to obtain a transition moment of (0.0508 plus or minus 0.0015) x 10 to the minus 18th esu cm. This work appears to resolve some earlier difficulties in interpreting measurements and calculations of intensities in nu4 of CH4.

Fox, K.↗
NASA NTRS1980

long wavelength Pb(1-x)Sn(X)Se and Pb(1-x)Sn(x)Te diode lasers as local oscillators

A breadboard heterodyne receiver is described which was used to establish the characteristics of lead salt diode lasers pertinent to their use as local oscillators using laser devices operating in the 15-25 micrometer spectral region. Heterodyne detection efficiency is directly correlated with the transverse mode structure and emphasizes the necessity of stable lowest order mode operation for lasers when used as local oscillators. The results obtained indicate that the continued development of these lasers provide suitable local oscillators for a variety of applications.

Washwell, E. R.↗
NASA NTRS1987

Tunable diode laser measurements of formaldehyde foreign-gas broadening parameters and line strengths in the 9-11-micron region

A tunable diode laser spectrometer has been used to determine pressure broadening coefficients due to collision with the foreign gases air, H2, O2, and N2 in the nu4 and nu6 bands of H2CO between 9 and 11 microns. Absolute line strengths for twenty-eight transitions have also been determined. The broadening coefficients are very similar to theoretical literature values in the cases of air, N2, and O2. The H2-H2CO values are in good agreement with earlier experimental millimeter-wave results.

Nadler, Shachar↗
NASA NTRS1985

Tunable diode laser mesurements of widths of air- and nitrogen-broadened lines in the nu(4) band of C-13H4

Tunable diode laser measurements of air-broadened and N2-broadened halfwidths are reported for 23 lines in the nu(4) band of C-13H4, between 1260 and 1360/cm. For all lines, at least three scans of each of four or more pressures were recorded. The experimental halfwidths presently obtained for C-13H4 are both larger and smaller than the U.S. Air Force Geophysics Laboratory values.

Devi, V. M.↗
NASA NTRS1998

Diode laser absorption sensors for gas-dynamic and combustion flows

Recent advances in room-temperature, near-IR and visible diode laser sources for tele-communication, high-speed computer networks, and optical data storage applications are enabling a new generation of gas-dynamic and combustion-flow sensors based on laser absorption spectroscopy. In addition to conventional species concentration and density measurements, spectroscopic techniques for temperature, velocity, pressure and mass flux have been demonstrated in laboratory, industrial and technical flows. Combined with fibreoptic distribution networks and ultrasensitive detection strategies, compact and portable sensors are now appearing for a variety of applications. In many cases, the superior spectroscopic quality of the new laser sources compared with earlier cryogenic, mid-IR devices is allowing increased sensitivity of trace species measurements, high-precision spectroscopy of major gas constituents, and stable, autonomous measurement systems. The purpose of this article is to review recent progress in this field and suggest likely directions for future research and development. The various laser-source technologies are briefly reviewed as they relate to sensor applications. Basic theory for laser absorption measurements of gas-dynamic properties is reviewed and special detection strategies for the weak near-IR and visible absorption spectra are described. Typical sensor configurations are described and compared for various application scenarios, ranging from laboratory research to automated field and airborne packages. Recent applications of gas-dynamic sensors for air flows and fluxes of trace atmospheric species are presented. Applications of gas-dynamic and combustion sensors to research and development of high-speed flows aeropropulsion engines, and combustion emissions monitoring are presented in detail, along with emerging flow control systems based on these new sensors. Finally, technology in nonlinear frequency conversion, UV laser materials, room-temperature mid-IR materials and broadly tunable multisection devices is reviewed to suggest new sensor possibilities.

Non-NASA Center↗
NASA NTRS1980

Intermode calibration of diode-laser spectra using tandem etalons

The paper deals with an approach which can improve the accuracy of etalon calibration of tunable diode-laser (TDL) spectra in the IR and extend absolute calibration among several isolated modes. Two etalons placed in the laser beam produce a combined fringe pattern that, with the aid of a monochromator mode selector, can be used to establish the number of fringes between any two spectral points separated by a large frequency interval. This technique has been applied to several similar cases for calibration of isolated modes or verification of the identity of lines of known frequency.

Jennings, D. E.↗
NASA NTRS1988

Efficient second harmonic generation of a diode-laser-pumped CW Nd:YAG laser using monolithic MgO:LiNbO3 external resonant cavities

56-percent efficient external-cavity-resonant second-harmonic generation of a diode-laser pumped, CW single-axial-mode Nd:YAG laser is reported. A theory of external doubling with a resonant fundamental is presented and compared to experimental results for three monolithic cavities of nonlinear MgO:LiNbO3. The best conversion efficiency was obtained with a 12.5-mm-long monolithic ring cavity doubler, which produced 29.7 mW of CW, single-axial model 532-nm radiation from an input of 52.5 mW.

Kozlovsky, William J.↗
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↗
DOE OSTI2023

Engineered current-density profile diode laser

The present technology can be used to control the current injection profile in the longitudinal direction of a high-power diode laser in order to optimize current densities as a function of position in the cavity to promote higher reliable output power and increase the electrical to optical conversion efficiency of the device beyond the level which can be achieved without application of this technique. This approach can be utilized, e.g., in the fabrication of semiconductor laser chips to improve the output power and wall plug efficiency for applications requiring improved performance operation.

Leisher, Paul O.↗