Generation of short laser pulses

Progress in the technology of ultrashort pulse generation during the last years is outlined. After a short reminder of the basic active/passive mode locking processes and the combined pulse forming action of passive mode locking and gain saturation in the colliding-pulse mode locking arrangement (CPM), the recently developed coupled cavity/additive pulse mode locking (CCM/APM) configurations are reviewed. The Kerr lens mode locking (KLM) process constitutes an important advance towards simplicity and reliability. Its lack of a self-starting property has been of concern, but can finally be overcome by custom-built semiconductor nonlinear absorbers. Reduction of the thermal load of the active materials, higher output efficiencies and much enhanced beam quality result from the use of laser diodes to pump solid state lasers. Synchronisation of the process of picosecond laser pulse generation with an external signal with subpicosecond phase jitter is an important subject. As an illustration the CERN synchro laser system in use at the CLIC test facility for the generation of short electron bunches is presented. Possibilities for future improvements in this system as a consequence of recent technological advances are indicated.