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  • LASERS AND MASERS  (6)
  • 1
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    Infrared-pumped third-harmonic and sum-frequency generation in diatomic molecules (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Using molecular hydrogen as a model system, we present a calculation which demonstrates the feasibility of efficient third-harmonic and sum-frequency generation of IR laser radiation by diatomic molecular gases. A conversion efficiency of 10% without phase matching is achievable with a modest laser intensity of about 20 MW/sq cm. In addition to a two-photon resonance, the efficient conversion depends on a mechanism which makes use of virtual vibronic transitions exclusively. Possible methods for phase matching are also suggested.
    Keywords: LASERS AND MASERS
    Type: Applied Physics Letters; 27; July 15
    Format: text
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  • 2
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    IR pumped third-harmonic generation and sum-frequency generation in diatomic molecules (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The potential efficiency of using nonlinear up-conversion techniques for the high efficiency type lasers (CO,CO2, and chemical) is assessed. Results indicate that: the small pump photon energy necessitates the use of molecular media for conversion if resonance enhancement is to be used and that molecular systems present several problems. These difficulties include: their levels are complex; their transition probabilities are often unknown; and the oscillator strengths among vibrational levels in the ground electronic state of a molecule are much smaller than those among electronic states of an atom, thus limiting the magnitude of nonlinear interactions. It is shown that this problem can be eliminated by making use of vibronic transitions which, being primarily electronic transitions have much larger matrix elements and efficient conversion can be achieved with molecular systems.
    Keywords: LASERS AND MASERS
    Type: 2d NASA Conf. on Laser Energy Conversion; p 81-87
    Format: application/pdf
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  • 3
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    Velocity measurements by laser resonance fluorescence (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The photonburst correlation method was used to detect single atoms in a buffer gas. Real time flow velocity measurements with laser induced resonance fluorescence from single or multiple atoms was demonstrated and this method was investigated as a tool for wind tunnel flow measurement. Investigations show that single atoms and their real time diffusional motion on a buffer gas can be measured by resonance fluorescence. By averaging over many atoms, flow velocities up to 88 m/s were measured in a time of 0.5 sec. It is expected that higher flow speeds can be measured and that the measurement time can be reduced by a factor of 10 or more by careful experimental design. The method is clearly not ready for incorporation in high speed wind tunnels because it is not yet known whether the stray light level will be higher or lower, and it is not known what detection efficiency can be obtained in a wind tunnel situation.
    Keywords: LASERS AND MASERS
    Type: NASA-CR-163971
    Format: application/pdf
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  • 4
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    Third-order nonlinearities in molecular hydrogen - Two-photon resonance enhanced third-harmonic generation and Raman scattering (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Effects of quantum mechanical interferences on third-order susceptibilities in molecules are studied. First principle calculations for molecular hydrogen are presented and shown to agree with results derived from experimental stimulated Raman gain and spontaneous Raman cross-section data. 10 percent third-harmonic conversion efficiency in H2 at 1 atm without phase matching should require a 150 MW per sq cm at 4.81 microns. As little as 5.9-MW power is sufficient when the beam is properly focused. Resonance Raman scattering (RRS) is proposed for experimentally investigating the interference effects, which tend to reduce the strength of third-order nonlinear susceptibilities.
    Keywords: LASERS AND MASERS
    Type: IEEE Journal of Quantum Electronics; QE-13; Sept
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  • 5
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    Two-frequency lidar technique for mesospheric Na temperature measurements (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper describes a new two-frequency lidar for measuring Na temperature profiles. The laser oscillator is tuned to the two operating frequencies by observing the Doppler-free structure of the Na D2 fluorescence spectrum in a vapor cell. The lidar technique and initial observations of the temperature profile between 82 and 102 km are described. Absolute temperature accuracies at the Na layer peak of better than + or - 3 K with a vertical resolution of 1 km and an integration period of approximately 5 min were achieved.
    Keywords: LASERS AND MASERS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 929-932
    Format: text
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  • 6
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    Optical Stark effect in the four-wave mixing and stimulated Raman spectra of N2 (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The influence of the optical Stark effect on spectral line shapes in four-wave-mixing Raman spectroscopy (FWMRS) and stimulated Raman spectroscopy (SRS) is investigated experimentally and theoretically. Using an experimental setup capable of rapid alternation between the simultaneous measurement of coherent Stokes Raman spectroscopy and inverse Raman spectroscopy at low and high intensities, together with a sophisticated frequency reference scheme, it was possible to perform a rather direct comparison between Stark-broadened and non-Stark-broadened spectra of both classes of Raman spectroscopies. The results demonstrate that SRS spectra show more Stark shift and broadening than their FWMRS counterparts. A discrepancy with theoretical results is pointed out, and an attempt is made to explain it.
    Keywords: LASERS AND MASERS
    Type: Physical Review A - General Physics, 3rd Series (ISSN 0556-2791); 40; 6983-699
    Format: text
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