Stable high-energy, high-repetition-rate, frequency doubling in a large aperture temperature-controlled LBO at 515 nm
Jonathan Phillips, Saumyabrata Banerjee, Klaus Ertel, Paul Mason, Jodie Smith, Thomas Butcher, Mariastefania De Vido, Chris Edwards, Cristina Hernandez–Gomez, John Collier
Abstract
We report on frequency doubling of high-energy, high-repetition-rate ns pulses from a cryogenically gas cooled, multi-slab Yb:YAG laser system, using a type-I phase-matched lithium triborate (LBO) crystal. Pulse energy of 4.3 J was extracted at 515 nm for a fundamental input of 5.4 J at 10 Hz (54 W), corresponding to a conversion efficiency of 77%. However, during long-term operation, a significant reduction of efficiency (more than 25%) was observed owing to the phase mismatch arising due to the temperature-dependent refractive index change in the crystal. This forced frequent angle tuning of the crystal to recover the second-harmonic generation (SHG) energy. More than a five-fold improvement in energy stability of SHG was observed when the LBO crystal was mounted in an oven, and its temperature was controlled at 27°C. Stable frequency doubling with 0.8% rms energy variation was achieved at a higher input power of 74 W when the LBO temperature was controlled at 50°C.