Enhanced efficiency of UV second harmonic and sum frequency generation from copper vapor lasers

The authors have generated over 460-mW output power at 255.1 and 271.2 nm with a wall-plug efficiency of 0.016% and 300 mW at 289.1 nm with a wall-plug efficiency of 0.0008%. Using an off-axis unstable resonator matched to the plasma-tube geometry and gain characteristics along with focusing lenses with reduced achromatic and spherical aberration has allowed the highest efficiencies for nonlinear UV generation from a CVL (copper vapor laser) reported to date. Current UV output powers are limited by crystal damage which may be reduced by modifying the delivery optics.<
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