Self-focusing in mode-locked neodymium:glass laser oscillators

Self-focusing and self-phase modulation limit the power and distort the output of mode-locked neodymium-glass lasers. Self-focusing alone, only one aspect of the complicated development of pulsed mode-locked oscillation, is considered. Theoretical calculations show that the fundamental transverse mode is not stable in high peak-power laser oscillators. Self-focusing distortion of the transverse intensity distribution limits peak-power density to a few times 10⁸W/cm². At high power the transverse field distribution changes drastically from one cavity transit to the next, and similar changes occur within individual mode-locked pulses.