Experimental Verification of the Origin of Conical Emission During Filamentation

Summary form only given. In this paper we investigate experimentally the origin of conical emission utilizing pump-probe method. To check the role of four-wave mixing process, we tried to amplify weak probe radiation in filament created by powerful pulse. The 2 mJ 70 fs 800 nm pulse was spitted in two parts. The weak one with energy of 50 muJ was used for generation of white light which was used as probe radiation. The main part created filament in 1 cm fused silica plate. Angles between beams were chosen to satisfy phase-matching conditions of eventual parametric process. We did not observe any amplification. At the instant of temporal overlapping of the pulses, the filament served as a positive lens, decreasing the divergence of probe radiation.