Type-I walk-off compensated second and fourth harmonic generation of Nd:YAG laser radiation from a Li2B4O7 crystal

A type-I walk-off compensation (WOC) arrangement has been made for the second harmonic generation (SHG) and the fourth harmonic generation (FOHG) of commercially available e-switched Nd:YAG laser radiation, for the first time, using two identically cut Li2B4O7 crystals. The enhancement of the conversion efficiencies has been realized in the WOC arrangement by a factor of 2.71 for the SHG and 2.65 for the FOHG relative to the double-crystal non-walk-off arrangement. The absolute values of the conversion efficiencies obtained for WOC SHG and FOHG are 3.52% and 3.56% respectively, applying input power densities for the fundamental and second harmonic of the Nd:YAG laser beam at only 28.3 MW cm(-2) and 11.7 MW cm(-2), respectively.