Abstract: A solid state laser is provided including a rare earth-doped YAG, YLF, YVO, GSGG, YALO or GdVO oscillator crystal, at least one laser diode pumping source, a Q-switch short pulse generator, a frequency doubling stage and frequency quadrupling or quintupling stages. The frequency quadrupling or quintupling stages include a nonlinear optical crystal such as CLBO, BBO or LBO built into a housing. The housing is sealed off to prevent external moisture and other atmospheric impurities from accessing the crystal at its interior. The housing interior is configured for purging with one or more external inert gases or dry air through valve controls. The housing is equipped with a mechanism for controlling the temperature of the interior of the housing, and consequently for controlling the temperature of the crystal. The temperature controlling mechanism enables heating and cooling of the crystal, as well as maintaining the crystal at a constant selected temperature.