We report on the design and operation of an optimized version of aQ‐switched, mode‐locked, and cavity‐dumped ruby‐laser oscillator. The modulator window is much narrower than that assumed in conventional active mode‐lock theory, and is shown to yield much shorter pulses than the latter in cases where the number of round trips is restricted. To allow a high‐power pulse (≊1 GW) to evolve in the oscillator, and to allow simple synchronization to a (∼100 ns fixed delay) CO2laser, a limit of 23 round trips was chosen, but similar limits may be imposed by lasers having short‐gain duration as in an excimer laser. Details are given on the single spark gap switching element and Pockels cells, with an analysis of their expected switching speeds, in order to establish the effectiveness of the modulator, as compared to conventional sinusoidally driven active mode lockers. Single pulses of 50–70 mJ are reliably cavity‐dumped after only 100‐ns delay (23 round trips) with pulse length adjustable from 50–100 ps with ±5‐ps stability. Relative timing between the main (CO2) and probe (ruby) pulses allows a measurement accuracy of ±50 ps to be attained.