Self-starting Nd:YAG holographic laser oscillator with a thermal grating

Self-starting operation of a self-conjugating loop oscillator is achieved, for the first time to our knowledge, by use of an optically induced thermal hologram in a nonsaturable absorbing medium. Self-Q-switched single-longitudinal-mode pulses of 12-ns duration are obtained in a near-diffraction-limited spatial mode and with an output energy of >250 mJ . Good correction of intracavity phase distortions is obtained, as well as good extraction efficiency in the laser mode volume. It is shown that one has to set an additional nonreciprocal phase-shift element in the loop to ensure resonant operation of the system.