Influence of ellipticity of nanorods on both TPA of femtosecond laser pulse and transformation of pulse spectrum

Abstract

We investigate the femtosecond pulse propagation in medium with nanorods under the conditions of both changing the ellipticity (aspect ratio) of nanorods and dependence of TPA from aspect ratio of nanoparticles. The relation between the width of nanorods absorption spectrum and width of laser pulse spectrum as well as detuning of central frequency of absorption spectrum from carrier frequency of wave packet is taken into account at analyzing the laser pulse propagation. This detuning leads to appearance of phase grating which can essentially influence on the laser pulse propagation and compensate the action of pure amplitude grating caused by nonlinear absorption. We found that under certain conditions the distortion of laser pulse spectrum is really absent despite action of various nonlinearities. The second very important effect consists in substantial shift of maximal intensity in time domain due to spectrum self-modulation because of induced pure amplitude grating. This leads to light slowing-down. It should be emphasized that this effect is similar to spatial motion of maximal laser intensity at infrared optical radiation propagation in clouds.