Conical emission properties associated with atmospheric self-focussing femtosecond pulse propagation

Summary form only given. Numerous groups have demonstrated that tabletop high peak power femtosecond lasers are capable of inducing nonlinear self-focused propagation in atmosphere at 800 nm. The phenomenon unfailingly exhibits (1) light concentration in long single or multiple filaments of the order of 150 /spl mu/m diameter and tens of meters in length; (2) conical emission associated with these filaments has a considerably wider spectral content than the original laser pulse. Conical emission became apparent after the filaments were formed. While the divergence angle of these conical emissions has been studied, unfortunately there is no reasonable model proposed that can qualitatively describe (Brodeur et al, 1996; Nibbering et al, 1996) even the most basic features such as divergence angles of the different colors. Furthermore, the color ordering of these conical emissions can be changed upon changing the chirp of the launched pulse. In this paper, we present conical emission data to show its behavior as the pulse is chirped. In addition, we also present the spectral distribution of the conical emissions and how it depends on chirp. Finally, we compare our result with numerical result of Gaeta (Phys. Rev. Lett. vol. 84, pp. 3582-3585, 2000).