Lasing of <i>N</i>2+ induced by filamentation in air as a probe for femtosecond coherent anti-Stokes Raman scattering
Xiaodong Zhao, Stefan Nolte, Roland Ackermann
Abstract
We investigated ultrashort pulse filamentation and lasing action of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msubsup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi>N</mml:mi> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math> for pump-probe experiments in gases. Using femtosecond coherent anti-Stokes Raman scattering, the white-light supercontinuum generated in the filament was used to excite ro-vibrational Raman transitions in air, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">C</mml:mi> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">C</mml:mi> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> </mml:mrow> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> </mml:math> . We show that the lasing pulse acts as a probe for the excited levels by detecting the corresponding anti-Stokes Raman spectroscopy signals. This feature may be applied to remote sensing applications, as the temporal and spatial alignment of the probe beam and the filament is intrinsically provided.