Visualization Of Focusing-refocusing Cycles During Filamentation In Baf_2

摘要

Filamentation occurs within a 1.5 cm-long crystal of BaF_2 during the propagation of intense, ultrashort (40 fs) pulses of 800 nm light; a systematic study as a function of incident power enables us to extract quantitative information on laser intensity within the condensed medium, the electron density and the six-photon absorption cross section. At low incident power, a single filament is formed within the crystal; two or more filaments are observed along the direction transverse to laser propagation at higher incident powers. Further, due to fluorescence from six-photon absorption (6PA), we are able to map the intensity variation in the focusing-refocusing cycles along the direction of laser propagation. At still higher incident powers, we observe splitting of multiple filaments. By measuring the radius (L_(min)) of single filament inside BaF_2, we obtain estimates of peak intensities (Imax) and electron densities (ρ_(max)) to be 3.26 × 10~(13) Won~(-2) and 2.81 × 10~(19) cm~(-3), respectively. Use of these values enables us to deduce that the 6PA cross-section in BaF_2 is 0.33 × 10~(-70) cm~(12) W~(-6) s~(-1).