Abstract

The pump-to-signal conversion efficiency of the optical parametric amplifiers (OPA) is usually limited to about 20% and further amplification is accompanied by the degrading pulse and beam quality. Typically, the limiting factor here is the back-conversion process that (for Gaussian pulsed-beams) commonly starts at the full on-axis pump depletion. Back-conversion can be suppressed by eliminating the idler wave from the interaction before the pump wave is depleted. This was previously achieved by employing non-collinear pump recycling schemes [1] and idler absorbtion [2]. Nevertheless, when compared to the currently exploited standard solutions, these approaches tend to either consume a lot of space, demand exotic materials or lack tunability. In this work we propose and experimentally test a polarization-based idler elimination scheme for the suppression of the back-conversion in femtosecond OPA that is simple, compact, requires relatively inexpensive tools and preserves the wavelength tunability of the light source. This is achieved by using two consecutive crystals (see Fig. 1a.) cut for different nonlinear interaction types (type-I and type-II) in the same amplification stage. Idler wave, generated in the first crystal, cannot participate in the second interaction, because its polarization state is not supported by the nonlinear process. The enhanced idler amplification can also be achieved by rotating the type-II crystal for an interaction that satisfies the phase-matching conditions for o-polarized idler wave (see Fig. 1a.). We used a delay crystal in between the amplification crystals that compensates the temporal walk-off between pump and signal. This approach was tested by boosting the energy of the pre-amplified and temporally stretched white-light continuum.

© 2023 IEEE