Cone emission induced by femtosecond excitation in rubidium vapor

Abstract

We studied the emission from dense rubidium vapor under 100-fs pulsed laser excitation in the 730--820 nm range. Self-focusing along with a conical emission (CE) was observed for the excitation in the blue wing of $D2$ atomic resonance. Self-defocusing occurred for the red-wing excitation. This is in accordance with the theory of the intensity dependent nonlinear refraction index. In the case of the CE observation, our experimental results are attributed to the self-phase modulation of the laser beam interacting with the near-resonant atomic medium.