We demonstrate that a femtosecond-laser filament in both molecular and atomic gases is birefringent for a copropagating probe pulse. Any input-probe polarization is decomposed into two orthogonal components, the optical axis being in the pump polarization direction. In molecular gases, the birefringence is mainly due to the delayed rotational molecular-wave packet; the probe pulse thus experiences several revivals in time. The two probe components end up spatially separated in the far field. In atomic gases such as argon, the effect is weaker and is attributed to the instantaneous electronic cross-phase modulation.
© 2009 Optical Society of America
Original Manuscript: December 16, 2008
Revised Manuscript: March 24, 2009
Manuscript Accepted: March 30, 2009
Published: April 27, 2009
Claude Marceau, Yanping Chen, Francis Théberge, Marc Châteauneuf, Jacques Dubois, and See Leang Chin, "Ultrafast birefringence induced by a femtosecond laser filament in gases," Opt. Lett. 34, 1417-1419 (2009)