A new walk-off compensated multipass scheme for large enhancement of conversion efficiency for fourth harmonic generation

A significant enhancement is treated in the energy of a fourth harmonic generated beam (266 nm) by employing the new technique of walk-off compensated multipass configuration without any change either in the beam parameters or in the intensity of the input fundamental laser radiation. As much as 56% conversion efficiency is obtained in twin lithium tetraborate crystals, even though the effective nonlinear coefficient of the crystal is as low as 1/6th that of KDP. Apart from crystals that have large walk-off angles, low effective nonlinear coefficients, or both, the simple experimental set-up would also be quite suitable for those crystals, especially infrared crystals that have large effective nonlinear coefficients but low laser damage thresholds.