Second Harmonic Generation under Strong Influence of Dispersion and Cubic Nonlinearity Effects

Abstract

High intensity contrast ratio (ICR) is required for majority of experiments with strong-field radiation. The demands to temporal intensity profile are determined by task of application of super strong radiation. As a rule, the experiments require ICR as higher as possible. SHG process of powerful femtosecond radiation is known to be an excellent approach to significant enhancement of a temporal intensity profile. The peak power of output radiation of modern laser complexes exceeds the petawatt level (Aoyama, Yamakawa et al. 2003; Lozhkarev, Freidman et al. 2007; Liang, Leng et al. 2007 ; Yanovsky, Chvykov et al. 2008 ) and power density in the radiation is in a range of 10TW/cm2. At such high intensities cubic polarization of frequency doubling media is needed to be taken into consideration. The polarization leads to nonlinear phase accumulation of interacted waves (Razumikhina, Telegin et al. 1984; Choe, Banerjee et al. 1991; Chien, Korn et al. 1995; Ditmire, Rubenchik et al. 1996; Mironov, Lozhkarev et al. 2009) and small-scale self-focusing (SSSF) appearance (Bespalov and Talanov 1966; Rozanov and Smirnov 1980; Lowdermilk and Milam 1981; Kochetkova, Martyanov et al. 2009; Poteomkin, Martyanov et al. 2009). The present research is devoted to demonstration of a possibility of SHG process implementation for ICR enhancement. In the chapter, we present theoretical and experimental results of SHG of output radiation of petawatt level femtosecond laser (Lozhkarev, Freidman et al. 2007). The influence of cubic polarization and dispersion effects are taken into account in the theoretical model. The coincidence of experimental results and the observed theoretical model are thoroughly discussed in section 2. Numerical simulation of SHG process has made it possible to demonstrate the possibility of ICR enhancement. We suggested a technique of additional pulse compression after SHG process. Results of the theoretical explorations are presented in section 3. The model of linear stage of plane wave instability in media with quadratic and cubic nonlinearity is developed. The model is the generalization of the classical theory of beam