Self-focusing of high-power optical pulses in third harmonic generation under conditions of coherent two-photon interaction with matter

A numerical analysis is made of a self-consistent system of equations describing resonant two-photon interaction between light and a medium. The radiation pulse duration is assumed to be short compared with the phase relaxation time (coherent interaction). Allowance is made for the transverse structure of the fundamental-frequency and third-harmonic pulses. It is found that under certain conditions, the resultant self-focusing increases the efficiency of energy transfer from the pump pulse to the third-harmonic radiation.