Influence of absorption spectrum width of nanorods on TPA of femtosecond laser pulse

Abstract

We investigate a femtosecond pulse propagation in the medium, containing nanorods, with taking into account the dependence of TPA from the aspect ratio of nanorods. The influence of detuning between the central frequency of the absorption spectrum and the central frequency of spectrum of the laser pulse is considered as well as the dependence of the absorption spectrum on the aspect ratio of nanorods. We consider two important cases: formation of pure absorptive grating and formation of both absorptive and refractive gratings due to detuning of central frequency of wave packet from central frequency of absorption spectrum. Under the weak absorption we found out the acceleration of light or slowing of light (fast light or slow light) in comparison with light propagation in the linear medium. Using spatial-temporal analogy, one can see that this phenomenon is similar to the displacement of the laser beam centre in moving medium under thermal response or under thermal response and evaporation of clouds and fogs. The direction of the motion is perpendicular to the direction of incident laser beam. We found out also the soliton formation under neglecting of the nonlinear absorption: a depletion of laser energy is close to zero.