The remote detection of gas phase molecules remains a challenge. Laser filamentation can be used to enhance the cross section for Raman scattering of gas phase molecules on the order of 106–fold through impulsive excitation of vibrational modes of motion. The filament self shortens from 50 fs to <10 fs through the nonlinear processes of Kerr lensing, multiphoton ionization and self steepening. This pulse is short enough to coherently excite all Raman active modes of a medium including trace molecules in the gas phase. A probe pulse passing through the medium acquires measurable Raman sidebands from the macroscopic time-dependent polarization. The principals of the method will be presented along with applications to signature molecules.
© 2012 Optical Society of AmericaPDF Article