Laser with high quality, stable output beam, and long life high conversion efficiency non-linear crystal

A pulse multiplier comprising:

• a laser system for generating an input laser pulse, the laser system comprising:
• a light source;
• an annealed, frequency-conversion crystal having a length approximately equal to a smaller of twice a Rayleigh range in a non-walk-off direction and a length of twice a beam waist radius in a walk-off direction divided by a walk-off angle in radians;
• a housing to maintain an annealed condition of the crystal during standard operation at a low temperature;
• first beam shaping optics configured to receive a beam from the light source and focus the beam to an elliptical cross section at a beam waist in or proximate to the crystal;
• and
• a harmonic separation block to receive an output from the crystal and generate therefrom the input laser pulse and at least one undesired frequency beam;
• a polarizing beam splitter that receives the input laser pulse;
• a wave plate for receiving light from the polarized beam splitter and generating a first set of pulses and a second set of pulses, the first set of pulses having a different polarization than the second set of pulses;
• and
• a set of mirrors for creating a ring cavity including the polarizing beam splitter and the wave plate, wherein the polarizing beam splitter transmits the first set of pulses as an output of the pulse multiplier and reflects the second set of pulses into the ring cavity.