ABSTRACT
Spectral broadening of 0.3 ps 515 nm laser pulse in a highly Raman-active BaWO4 crystal and fused silica demonstrates significantly different behavior with the incident pulse energy. While the broadening in fused silica is fairly symmetric with respect to the pump laser pulse wavelength, the Stokes wing broadening in the BaWO4 crystal is 2 times wider than that of anti-Stokes wing, the former demonstrating a step-like increase with the pulse energy. To the best of our knowledge, the obtained data are the first clear evidences of the following facts: (i) stimulated Raman scattering with sufficiently high efficiency of conversion to Stokes components slows down spectral broadening induced by self-phase modulation, and (ii) the mechanism of Kerr nonlinearity, which is responsible for self-phase modulation in BaWO4, is of orientational nature. The nonlinear refraction coefficient and its decay time following from our experiments with BaWO4 were estimated as n2≈6.4.10-15cm2/W and τNL≈0.35ps.
ABSTRACT
The influence of plasma channel length on an angular terahertz (THz) radiation distribution is experimentally studied for the channel formed under filamentation of an ultrashort laser pulse. It is shown that the angular distribution of the THz emission depends only on laser intensity in the filament and plasma density of the plasma channel and does not depend on the plasma channel length. A qualitative explanation of the THz emission screening by the filament plasma channel is proposed.