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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Tunable cavity resonator with ramp shaped supports

A cavity for a hydrogen maser is described consisting of three parts which provide highly stable mechanical and thermal expansion characteristics for the cavity and ease of tuning. The three parts which are made of a glass ceramic material having a very small thermal expansion coefficient (1) a top plate, (2) a cylinder with three interrupted helical ramps at its bottom, and (3) a base which includes a bottom plate and three ramp lugs on which the helical ramps of the cylinder rest when the cylinder is placed on the base with the bottom plate in the cylinder. Cavity tuning is achieved by rotating the cylinder and thereby raising or lowering it on the base, which results in changing the cylinder volume by changing the distance between the bottom and top plates.

Vessot, R. F. C.↗
NASA NTRS1975

A tunable line filter polychromator for gas temperature measurements using laser Raman scattering

A proprietary laser line filter spectrograph (LLFS) was modified to test for improved remote measurement of atmospheric temperature by Raman spectroscopy of the rotational bands of N2 and O2. Both grating scan measurements with fixed PMT and polychromator image plane PMT scans with fixed grating setting were made using HeNe and Ar(+) lasers. The LLFS was found to have a laser line rejection ratio at 6A from the laser line and provides resolved rotational Raman spectral display at the polychromator exit plane. Spectral resolution is adequate to measure and correct for background in the Stokes spectrum. It is anticipated that this system should allow measurement of gas or atmospheric temperature to + or - 1 C.

Grossman, J. J.↗
NASA NTRS1975

Measurements of SO2 absorption coefficients using a tunable dye laser

High-resolution measurements of SO2 absorption coefficients in the UV are presented in the wavelength interval between 2962 and 3011 A using a frequency-doubled dye laser as the radiation source. These measurements have application to pollution monitoring of SO2 using the differential absorption scattering (DAS) technique. The spectral resolution of the measurements was 0.2 A (determined by the linewidth of the dye laser) and the generated spectra exhibited considerable rotational structure on the (000) double prime to (060) prime, (070) prime, and (080) prime electronic-vibrational transitions. The latter transitions correspond to center wavelengths of 3001.8, 2981.0, and 2962 A, respectively. The laser measurements were obtained with a signal-processing technique which eliminated calibration procedures associated with conventional optical-absorption measurements. Using this technique, the statistical uncertainty associated with measured absorption coefficients has been reduced to less than plus or minus 2% with a wavelength uncertainty of the laser source of plus or minus 0.1 A.

Thompson, R. T., Jr.↗
NASA NTRS1977

Tunable acoustical optical filter

Solid state filter with active crystal element increases sensitivity and resolution of passive and active spectrometers. Filter is capable of ranging through infrared and visible spectra, can be built as portable device for field use, and is suitable for ecological surveying, for pollution detection, and for pollutant classification.

Lane, A. L.↗
NASA NTRS1976

Intensity and pressure dependence of resonance fluorescence of OH induced by a tunable UV laser

The intensity and pressure dependence of the fluorescence spectrum of OH in the presence of N2 and H2O molecules was studied. Saturation of the absorption transition was observed at low pressures, and the corresponding fluorescence signal was found to vary as the square root of the exciting intensity. This observed dependence agreed with the predicted dependence which took into account the presence of laser modes in the spectrum of the exciting radiation. With full laser power incident, a saturation parameter as high as 3 x 10 to the 5th was observed. The fluorescence spectrum was found to peak at 3145 and at 3090 A, with the relative peak intensities dependent upon gas pressures and upon the particular rotational electronic transition used for excitation. It is concluded that vibrational relaxation of the electronically excited OH due to water vapor in the system plays a dominant role in determining the observed fluorescence spectrum.

Killinger, D. K.↗
NASA NTRS1977

Single heterostructure lasers of PbS/1-x/Se/x/ and Pb/1-x/Sn/x/Se with wide tunability

Single-heterostructure diode lasers formed by compositional interdiffusion (CID) and liquid-phase epitaxy (LPE) of lead salts are discussed. The CID technique, which involves creation of a single heterostructure in a pseudobinary compound having binary constituents with different vapor pressures, is reviewed; growth of lead-salt crystals of various compositions is described. Some electrical and optical characteristics, including properties indicative of high internal quantum efficiencies, are given for lasers which employ the CID and LPE diodes. High operating temperatures (i.e., liquid nitrogen levels and above), together with wide tuning ranges (a diode wavelength of 12.7 microns is reported), make the lasers useful in high-resolution spectrometry and advanced trace-gas monitoring systems.

Linden, K. J.↗
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 NTRS1979

Direct measurements of the Gibbs free energy of OH using a CW tunable laser

The paper describes an absorption measurement for determining the Gibbs free energy of OH generated in a mixture of water and oxygen vapor. These measurements afford a direct verification of the accuracy of thermochemical data of H2O at high temperatures and pressures. The results indicate that values for the heat capacity of H2O obtained through numerical computations are correct within an experimental uncertainty of 0.15 cal/mole K.

Killinger, D. K.↗
NASA NTRS1980

Far-field radiation pattern of tunable diode lasers

Technique rapidly determines far-field spatial energy distribution. Method takes about 3 minutes. It is optically simple and is economical, using standard laboratory parts and equipment. It records automatically without operator control and is easily adaptable to computer control of input instructions and computer treatment of output data. Degree of data resolution is limted only by width of recorder pen, and data are repeatable.

Lash, T. J.↗
NASA NTRS1980

Advances in tunable diode laser technology

The improvement of long-term reliability, the purification of mode properties, and the achievement of higher-temperature operation were examined. In reliability studies a slow increase in contact resistance during room temperature storage for lasers fabricated with In-Au or In-Pt contacts was observed. This increase is actually caused by the diffusion of In into the surface layer of laser crystals. By using a three layered structure of In-Au-Pt or In-Pt-Au, this mode of degradation was reduced. In characterizing the mode properties, it was found that the lasers emit in a highly localized, filamentary manner. For widestripe lasers the emission occurs near the corners of the junction. In order to achieve single-mode operation, stripe widths on the order of 8-10 micrometers are needed. Also, it was found that room temperature electroluminescence is possible near 4.6 micrometers.

Lo, W.↗
NASA NTRS1980

Reliability improvements in tunable Pb1-xSnxSe diode lasers

Recent developments in the technology of Pb-salt diode lasers which have led to significant improvements in reliability and lifetime, and to improved operation at very long wavelengths are described. A combination of packaging and contacting-metallurgy improvements has led to diode lasers that are stable both in terms of temperature cycling and shelf-storage time. Lasers cycled over 500 times between 77 K and 300 K have exhibited no measurable changes in either electrical contact resistance or threshold current. Utilizing metallurgical contacting process, both lasers and experimental n-type and p-type bulk materials are shown to have electrical contact resistance values that are stable for shelf storage periods well in excess of one year. Problems and experiments which have led to devices with improved performance stability are discussed. Stable device configurations achieved for material compositions yielding lasers which operate continuously at wavelengths as long as 30.3 micrometers are described.

Linden, K. J.↗