Standoff spectroscopy via remote generation of a backward-propagating laser beam

Philip R. Hemmer, Richard B. Miles, Pavel Polynkin, Torsten Siebert, Alexei V. Sokolov, Phillip Spranglee, Marlan O. Scully

Research output: Contribution to journalArticle

136 Scopus citations

Abstract

In an earlier publication we demonstrated that by using pairs of pulses of different colors (e.g., red and blue) it is possible to excite a dilute ensemble of molecules such that lasing and/or gain-swept superradiance is realized in a direction toward the observer. This approach is a conceptual step toward spectroscopic probing at a distance, also known as standoff spectroscopy. In the present paper, we propose a related but simpler approach on the basis of the backward-directed lasing in optically excited dominant constituents of plain air, N2 and O2. This technique relies on the remote generation of a weakly ionized plasma channel through filamentation of an ultraintense femtosecond laser pulse. Subsequent application of an energetic nanosecond pulse or series of pulses boosts the plasma density in the seed channel via avalanche ionization. Depending on the spectral and temporal content of the driving pulses, a transient population inversion is established in either nitrogen- or oxygen-ionized molecules, thus enabling a transient gain for an optical field propagating toward the observer. This technique results in the generation of a strong, coherent, counter-propagating optical probe pulse. Such a probe, combined with a wavelength-tunable laser signal(s) propagating in the forward direction, provides a tool for various remote-sensing applications. The proposed technique can be enhanced by combining it with the gain-swept excitation approach as well as with beam shaping and adaptive optics techniques.

Original languageEnglish (US)
Pages (from-to)3130-3134
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume108
Issue number8
DOIs
StatePublished - Feb 22 2011

Keywords

  • Air laser
  • Atmospheric surveillance
  • Raman
  • Threat detection

ASJC Scopus subject areas

  • General

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