We report a large peak power enhancement and reduction in pulse width for planar waveguide carbon dioxide lasers. Gain modulation through rf discharge power switching produces trains of laser pulses with peak power levels at up to 38 times the cw power level, with a pulse duration as low as 10 µs. Operation at repetition rates in the kHz region preserves the average power (100 W) of the normal cw/long pulse mode of operation. The laser is shown to operate close to the predicted boundaries dictated by thermal loading of the discharge. © 2001 American Institute of Physics.