Nonlinear phenomena in femtosecond laser systems based on Yb : YAG thin-rod amplifiers

Nonlinear effects in a high-power laser amplification system based on thin-rod active elements are experimentally investigated. It is shown that the most important nonlinear effect is the Kerr effect leading to self-focusing and self-phase modulation of laser radiation. The observed luminescence in Yb : YAG crystals in the visible region of the spectrum is caused by the charge transfer luminescence effect, which, in turn, is due to multiphoton absorption of laser radiation. Second-order nonlinearity in the crystal is used to effectively convert femtosecond pulses to second harmonic and sum-frequency waves which exhibit radiations of green and UV spectra.