High average power amplification of femtosecond pulses based on the Yb:CaYAlO₄ crystal

In this paper, we demonstrated the direct amplification of femtosecond pulses with the Yb:CaYAlO₄ crystal for the first time. A compact and simple two-stage amplifier delivered amplified pulses with the average powers of 55.4 W for σ-polarization and 39.4 W for π-polarization at the center wavelengthes of 1032 nm and 1030 nm, corresponding to 28.3% and 16.3% optical-to-optical efficiencies, respectively. These are to the best of our knowledge the highest value achieved with a Yb:CaYAlO₄ amplifier. Upon using a compressor consisting of prisms and GTI mirrors, a pulse duration of 166-fs was measured. Thanks to the good thermal management, the beam quality (M²) parameters <1.3 along each axis were maintained in each stage.