Comb generation of second and third harmonics at high intensive femtosecond pulse propagation in medium with quadratic and cubic nonlinearities

摘要

SHG is used in many practical applications such as a substance diagnostics, and imaging of various processes as well as for a frequency conversion of an optical pulse. As a rule, the frequency doubling is used also for a generation of the optical wave with tripled frequency by using the mixing of optical radiation with the basic and doubled frequencies. Nevertheless, THG can occur in a medium with cubic nonlinear response and in a medium with quadratic nonlinear response if the incident laser pulse intensity of the basic wave is enough high or if the intensities of the interacting waves increase until such values which are sufficient for occurring the cubic nonlinearity of a crystal. As a consequence, THG may occur. We investigate an efficiency of comb frequency generation if an intensity of the incident femtosecond pulse is sufficiently high . Obviously, one of these generation processes occurs with a big phase mismatching. We investigate comb generation efficiency in a dependence of the phase mismatching between interacting waves and other parameters. As a result, we observe various regimes of comb generation. It should be emphasized that we find out the generation regime with synchronic changing of the maximal intensities of all waves. At the same time, shape of the appearing sub-pulses at these frequencies are similar to Gaussian one. Our consideration is based on computer simulation with taking into account the SOD, phase mismatching, self-and cross-modulation for interacting waves.