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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Temperature and humidity profiles in the atmosphere from spaceborne lasers: A feasibility study

Computer simulations of the differential absorption lidar technique in a space craft for the purpose of temperature and humidity profiling indicate: (1) Current technology applied to O2 and H2O lines in the .7 to .8 micrometers wavelength band gives sufficiently high signal-to-noise ratios (up to 50 for a single pulse pair) if backscattering by aerosol particles is high, i.e. profiling accurate to 2 K for temperature and 10% for humidity should be feasible within the turbid lower troposphere in 1 km layers and with an averaging over approximately 100 pulses. (2) The impact of short term fluctuations in aerosol particle concentration is too big for a one laser system. Only a two laser system firing at a time lag of about 1 millisecond can surmount these difficulties. (3) The finite width of the laser line and the quasi-random shift of this line introduce tolerable, partly systematic errors.

Grassl, H.↗
NASA NTRS1977

Measurement of the fundamental vibration-rotation spectrum of ClO

The ClO fundamental absorption band near 850/cm is observed, with a tunable PbSnTe diode laser used as a source of monochromatic radiation. The chlorine monoxide concentration in the absorption tube was measured indirectly via a UV transmission technique. Frequencies and assignments for the ClO lines, and band centers and rotational constants for the ClO fundamental vibration, are tabulated. Diatomic vibration-rotation transitions within and between electronic substates are discussed. The tunable diode laser is valuable for studying the hyperfine structure. The IR spectroscopic technique is developed in order to monitor chlorine monoxide concentration in the stratosphere, since the short-lived ClO is a crucial intermediate participant in reactions involving destruction of stratospheric ozone.

Menzies, R. T.↗
NASA NTRS2011

Low Power Consumption Laser for Next Generation Miniature Optical Spectrometers for Trace Gas Analysis

The air quality of any manned spacecraft needs to be continuously monitored in order to safeguard the health of the crew. Air quality monitoring grows in importance as mission duration increases. Due to the small size, low power draw, and performance reliability, semiconductor laser-based instruments are viable candidates for this purpose. Achieving a minimum instrument size requires lasers with emission wavelength coinciding with the absorption of the fundamental absorption lines of the target gases, which are mostly in the 3.0-5.0 mu m wavelength range. In this paper we report on our progress developing high wall plug efficiency type-I quantum-well GaSb-based diode lasers operating at room temperatures in the spectral region near 3.0-3.5 mu m and quantum cascade (QC) lasers in the 4.0-5.0 mu m range. These lasers will enable the development of miniature, low-power laser spectrometers for environmental monitoring of the spacecraft

distributed feedback laser (DFB↗
DOE OSTI2022

Multi-species temperature and number density analysis of a laser-produced plasma using dual-comb spectroscopy

Dual-comb spectroscopy (DCS) represents a novel method of using absorption spectroscopy as a diagnostic tool for multispecies analysis of excitation temperatures and column densities in laser-produced plasmas (LPPs). DCS was performed on a LPP generated by ablating a multielement alloy containing Nd, Gd, and Fe. Transitions from all three elements were observed in absorption spectra measured from 530.08 to 535.19 nm at seven time-delays from 31 to 250 μs after ablation. The spectra were fit using a nonlinear regression algorithm to determine peak areas, and excitation temperatures and column densities were determined for the three atomic species separately using Boltzmann plots. The measured excitation temperatures of Nd I and Gd I showed good agreement at all time-delays, whereas the Fe I temperature was found to be higher, and the ratios between the column densities varied with delay. The observations are understood via effects of LPP spatial averaging, elemental fractionation, and molecular formation and are compared and contextualized with previous work studying LPPs using other spectroscopic techniques. A brief discussion of the precision and accuracy of the determined excitation temperatures and column densities is also presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1979

Lidar temperature profiling: Performance simulations of Masons method

Several methods of using lasers to measure atmospheric temperature profiles were described. Mason's suggestion was analyzed here to assess its capabilities for various lidar configurations. Temperatures were inferred from a measure of the Boltzmann distribution of rotational states in one of the vibrational bands of O2. Differential absorption was measured using three tunable, narrowband pulsed lasers. The outputs of two were tuned to wavelengths at the centers of absorption lines at either end of a particular branch in the band. The third wave-length was in a region of no absorption; its lidar return measured only the atmospheric backscatter, and therefore allowed calculations of the absorption coefficients at the other two wavelengths as a function of altitude. From the ratio of the two line absorption coefficients plus a priori knowledge of the line parameters, the temperature-altitude profile were calculated.

Schwemmer, G. K.↗
DOE OSTI2020

Yb:Lu 2 O 3 hydrothermally grown single-crystal high-resolution absorption spectra obtained between 8 and 300 K

Here we present new high-resolution absorption data for the important sesquioxide laser material Yb:Lu 2 O 3 for the spectral range of 880–1020 nm, at various temperatures between 8 and 300 K, and for the zero-phonon region from 960 to 990 nm, at temperatures from 8 to 300 K. We have experimentally observed the C 3i (0,1)–(1,3) transition for the first time, located at 880.7 nm at 8 K. Based on high confidence fitting functions to the experimental data, we provide the first complete compilation of all observed electronic and electronic–vibrational transitions. Detailed fitting and plots of the C 2 and C 3i zero-line data show an evolution of the linewidth from being predominantly electronic below about 100 K to being dominated by thermal processes above 100 K. We have also found evidence for a “soft” phase transition between 80 and 100 K that changes the local coordination environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

Pre-resonance Raman spectra of some simple gases

The pre-resonance Raman spectra of SO2, N2O, and H2S were investigated using the 4880 A, 4727 A, and 4579 A lines of the argon ion laser. Although these molecules have electronic absorption bands in the near ultraviolet, none exhibit any pre-resonance enhancement within our experimental error of + or - 10%. Possible explanations taking into account the current theories for resonance Raman are discussed.

Low, P. W.↗
NASA NTRS1974

GaAs laser diode pumped Nd:YAG laser

A 1.5-mm by 3-cm neodymium-ion doped YAG laser rod has been side pumped using a GaAs laser diode array tuned to the 8680-A absorption line, achieving a multimode average output power of 120 mW for a total input power of 20 W to the final-stage laser diode drivers. The pumped arrangement was designed to take advantage of the high brightness of a conventional GaAs array as a linear source by introducing the pump light through a slit into a close-wrapped gold coated pump cavity. This cavity forms an integrating chamber for the pump light.

Conant, L. C.↗
NASA NTRS1975

Heterodyne spectroscopy of astronomical and laboratory sources at 8.5 microns using diode laser local oscillators

The first 8.5 microns infrared heterodyne spectrometer has been constructed using tuneable semiconductor (PbSe) diode lasers and was used to measure absorption line profiles of N2O in the laboratory, as well as black-body emission from the moon and from Mars. Spectral information was recorded over a 200 MHz bandwidth using an 8-channel filter bank. The resolution was 25 MHz (6 millionths of a micron), and the minimum detectable (black-body) power was approximately 1 times 10 to the minus 16th power W for 8 min of integration. The results demonstrate the usefulness of heterodyne spectroscopy for the study of remote and local sources in the infrared.

Mumma, M.↗
NASA NTRS1976

Outlook for metal lasers

Lasers utilizing atomic metallic vapors are considered with emphasis on a double discharge technique and multiply pulsed experiments. Data are presented on the effect of time delay after the first electrical discharge and the effect of lasant temperature along with results of absorption measurements utilizing a 13 mm diameter laser tube. Data obtained from multiply pulsed experiments for discharge diameters varying from 1 to 4 cm indicate that the efficiency increases with the pulsing rate.

Russell, G. R.↗
NASA NTRS1979

Remote measurement of tropospheric ozone

It is shown that a differential absorption lidar employing a pulsed CO2 laser and a direct detection receiver is capable of significantly improving the existing data base on the tropospheric ozone burden. As a ground-based system, the lidar could obtain urban to regional scale O3 measurements with a vertical or horizontal resolution of at least 1 km in the troposphere. As a space-based system, it could obtain global scale coverage of the O3 burden below the stratospheric maximum of O3.

Bufton, J. L.↗
NASA NTRS1979

Effect of rotational excitation on the band oscillator strength of OH

In the study described, a single-frequency tunable CW dye laser was used to obtain accurate absorption measurements of the band oscillator strength for various rotational-electronic lines in some transitions of OH. The band oscillator strength is shown to decrease linearly with the energy of rotational excitation. This decrease is attributed exclusively to the lengthening of the internuclear distance due to rotation.

Wang, C. C.↗
NASA NTRS1981

Temporal correlation measurements of pulsed dual CO2 lidar returns

A pulsed dual-laser direct-detection differential-absorption lidar DIAL system, operating near 10.6 microns, is used to measure the temporal correlation and statistical properties of backscattered returns from specular and diffuse topographic targets. Results show that atmospheric-turbulence fluctuations can effectively be frozen for pulse separation times on the order of 1-3 msec or less. The diffuse target returns, however, yielded a much lower correlation than that obtained with the specular targets; this being due to uncorrelated system noise effects and different statistics for the two types of target returns.

Menyuk, N.↗
NASA NTRS1983

The NASA/Goddard balloon borne lidar system

The present investigation represents a part of a NASA program which is concerned with a study regarding the seriousness of man-made stratospheric ozone depletion. Such a depletion could possibly be caused by exhaust gases of aircraft at high altitudes or the release of chlorofluorocarbons into the lower atmosphere. A balloon-borne optical radar system was employed to conduct ozone measurements in the altitude region from 21 to 36 km and hydroxyl radical measurements in the region from 33 to 36 km. The hydroxyl radical was determined by making use of a procedure which is based on fluorescence induced by laser radiation. The technique of differential absorption lidar (DIAL) was used to measure ozone. According to this technique, two wavelengths are transmitted simultaneously and their backscattered intensities are measured. the obtained results show that optical radar represents an effective tool for stratospheric investigations.

Heaps, W. S.↗
NASA NTRS1984

Laser thermal propulsion

Laser thermal propulsion (LTP) is studied for the case in which laser power is absorbed by a small very high-temperature plasma (about 20,000 K) and transferred to the remainder of the pure hydrogen propellant by radiation and mixing. This concept could lead to the realization of a lightweight orbital transfer vehicle propulsion system having a specific impulse in the range 1000-2000 s. Approximately 12 percent of the input power may be radiated to the thruster walls, and 15 percent of the total propellant flow must be heated to 20,000 K to provide a bulk temperature of 5000 K prior to expansion. Three principal research issues identified are: (1) conditions for hydrogen plasma ignition, (2) control of the plasma position within the laser beam, plasma stability, and plasma absorption efficiency, and (3) characterization of the mixing of the plasma and buffer flows.

Keefer, D.↗
NASA NTRS1985

Tunable diode laser Stark modulation spectroscopy for rotational assignment of the HNO3 7.5-micron band

The technique of Stark modulation spectroscopy for unraveling and assigning rotationally resolved dense molecular spectra has been employed using a tunable diode laser (TDL) source. Doppler-limited absorption and Stark modulation spectra of the HNO3 7.5-micron band near the 1326/cm band origin are presented with preliminary values of the excited-state rovibrational constants derived from both TDL and Bomem Fourier transform IR spectra.

Webster, C. R.↗