Laser pulse train management with an acousto-optic modulator

Photo injector laser systems for linac based Free Electron Lasers (FELs) sometimes have the capability of generating pulse trains with an adjustable length. For example, the currently installed laser at the Photo Injector Test Facility at DESY, Zeuthen Site (PITZ) can generate pulse trains containing up to 800 pulses. Repetition frequencies are 10 Hz for the pulse trains and 1 MHz for the pulses within a train, respectively [1]. Mostly due to thermal effects caused by absorption in amplifier and frequency doubling crystals, pulse properties are changing slightly within a pulse train and also shot-to-shot, depending on the pulse train length. To increase stability and repeatability it is desirable to run the laser under constant conditions. To achieve this while still being able to freely choose pulse patterns a pulse picker can be installed at the laser output to sort out unwanted pulses. A promising candidate for this functionality is an acousto-optic modulator which currently is being tested at PITZ. First experimental results will be presented and discussed towards the possibility of including this device into an FEL photo injector.