The YG900 modular Nd:YAG lasers manufactured by the Quantel Group’s Industrial & Scientific Laser Div. are based on an active/passive mode-locked oscillator to provide high repeatability and short pulses. The output coupler is a Fabry-Perot etalon that helps prevent feedback of energy into the oscillator and that protects the optics against damage. Via various etalons, the pulse durations can be changed from 35 to 200 ps. The result of the long stable resonator is a transverse single-mode TEM00 beam. Repetition rates are 10, 20 or 30 Hz, depending upon the model. All four models produce a pointing stability of <20 μrad and an energy stability of 5%, both at 1064 nm. Contrast ratio at 1064 nm is >200:1 for all models, and beam divergence is ≤0.5 mrad.