Abstract: A circuit is disclosed for controlling the output of a flashlamp used to excite a gain medium. The circuit functions to supply energy to the flashlamp for fixed time intervals to generate repetitive pulses having a uniform duration. The circuit includes a photodetector for generating an output signal which is proportional to the light generated by the flashlamp. During a first phase of the fixed interval, the circuit delivers a first voltage level to the flashlamp. At the end of the first phase, a comparison is made between the output of the flashlamp as measured by the photodetector and a target output level. The circuit also initiates a second, boost phase where the voltage supplied to the flashlamp is increased. The length of the boost phase is selected so that at the end of the fixed interval, the total light output generated by the flashlamp is substantially equal to the desired output level.