Ultrafast birefringence induced by a femtosecond laser filament in gases.
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.
Centre d'Optique, Photonique et Laser (COPL) and Département de Physique, de Génie Physique et d'Optique, Université Laval, Québec, Québec G1V 0A6, Canada. claude.marceau.2@ulaval.ca
Claude
C
Marceau
Yanping
Y
Chen
Francis
F
Théberge
Marc
M
Châteauneuf
Jacques
J
Dubois
See Leang
SL
Chin