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 seco nd harmonic generation (SHG) and the fourth harmonic generation (FOHG) of c ommercially available e-switched Nd:YAG laser radiation, for the first time , using two identically cut Li2B4O7 crystals. The enhancement of the conver sion 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-wa lk-off arrangement. The absolute values of the conversion efficiencies obta ined 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.