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Proceedings Paper

Atmospheric absorption versus deep ultraviolet (pre-)resonance in Raman lidar measurements
Author(s): Hans D. Hallen; Adam H. Willitsford; Ryan R. Neely III; C. Todd Chadwick; C. Russell Philbrick
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Paper Abstract

The Raman scattering of several liquids and solid materials has been investigated near the deep ultraviolet absorption features corresponding to the electron energy states of the chemical species present. It is found to provide significant enhancement, but is always accompanied by absorption due to that or other species along the path. We investigate this trade-off for water vapor, although the results for liquid water and ice will be quantitatively very similar. An optical parametric oscillator (OPO) was pumped by the third harmonic of a Nd:YAG laser, and the output frequency doubled to generate a tunable excitation beam in the 215-600 nm range. We use the tunable laser excitation beam to investigate pre-resonance and resonance Raman spectroscopy near an absorption band of ice. A significant enhancement in the Raman signal was observed. The A-term of the Raman scattering tensor, which describes the pre-resonant enhancement of the spectra, is also used to find the primary observed intensities as a function of incident beam energy, although a wide resonance structure near the final-state-effect related absorption in ice is also found. The results suggest that use of pre-resonant or resonant Raman LIDAR could increase the sensitivity to improve spatial and temporal resolution of atmospheric water vapor measurements. However, these shorter wavelengths also exhibit higher ozone absorption. These opposing effects are modeled using MODTRAN for several configurations relevant for studies of boundary layer water and in the vicinity of clouds. Such data could be used in studies of the measurement of energy flow at the water-air and cloud-air interface, and may help with understanding some of the major uncertainties in current global climate models.

Paper Details

Date Published: 13 May 2016
PDF: 11 pages
Proc. SPIE 9832, Laser Radar Technology and Applications XXI, 983210 (13 May 2016); doi: 10.1117/12.2224149
Show Author Affiliations
Hans D. Hallen, North Carolina State Univ. (United States)
Adam H. Willitsford, Johns Hopkins Univ. (United States)
Ryan R. Neely III, North Carolina State Univ. (United States)
C. Todd Chadwick, North Carolina State Univ. (United States)
C. Russell Philbrick, North Carolina State Univ. (United States)

Published in SPIE Proceedings Vol. 9832:
Laser Radar Technology and Applications XXI
Monte D. Turner; Gary W. Kamerman, Editor(s)

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