Optimization of line-focusing geometry for efficient nonlinear frequency conversion from copper-vapor lasers

Detailed parametric investigations of line foci for efficient nonlinear frequency conversion of copper-vapor lasers are presented. For a single medium-scale copper-vapor laser (nominally 20 W), the optimum focal geometry for efficient second-harmonic and sum-frequency generation in BBO is to focus a 3.75-mm-diameter beam into the crystal with an f=60 mm cylindrical lens, Using such a focal geometry, UV powers of up to 1.75 W (SHG of the green), 1.2 W (SHG yellow), and 1.5 W (SFG) have been produced with peak instantaneous conversion efficiency of up to 48%. Conversion efficiencies are most sensitive to the F-number of the cylindrical focusing, with the optimum F-number being approximately 16, and are relatively insensitive to the width of the focused beam.