Abstract: The present invention provides a jitter stable electro-optical modulator for modulating a high power, repetitively pulsed laser having an optical risetime (10% to 90%) of the order of nanoseconds. The electro-optical modulator includes a birefringent electro-optical device; a hydrogen thyratron operated at a preselected high pressure and having an "ON" and an "OFF" state; first means responsive to the "ON" state of the thyratron for impressing a first preselected voltage across the birefringent electro-optical device; second means responsive to the "OFF" state of the hydrogen thyratron for impressing a second preselected voltage across the electro-optical modulator at a time coincident with the laser buildup interval; and means for repetitively driving the hydrogen thyratron into the "ON" and the "OFF" states repetitively at a preselected repetition rate.