Research on Yb: CaYAlO4 regenerative amplifier

Attosecond science is one of the driving forces for the development of femtosecond amplifiers of high average power and ultrashort pulse duration. In this article, a theoretical and experimental study on the regenerative amplification based on Yb:CaYAlO4 crystal was carried out for the practical needs of high-repetition-rate attosecond light sources. In the theoretical study, a mode-tunable regenerative cavity with good thermal stability was designed based on the thermal lens calculations of Yb:CaYAlO4 crystal; the amplified output energies and spectra of π and σ polarization of the crystal were calculated. In the experiment that the π-axis of Yb:CaYAlO4crystal was parallel to the laser polarization, the laser amplifier emitted 1.61 mJ pulses at an average power of 16.1 W. Notably, the dip of the π-polarization emission spectrum near 1025.1 nm compensates the gain narrowing of the seed laser during amplification. Thus, the center wavelength and the spectral full width at half maximum of the amplified laser were 1030 nm and 16 nm in respective. Upon using a grating-pair for compression, 149 fs pulses with peak power of 9.5 GW were obtained. In comparison, the σ-polarization emission spectrum of Yb:CaYAlO4crystal is relatively flat in the range of 1000 to 1050 nm, but with a larger gain cross-section. When the laser polarization was parallel to the σ-axis of Yb:CaYAlO4crystal, 2.87 mJ pulses at 10 kHz repetition rate were achieved, with an average power of 28.7 W. In this case, the center wavelength and the spectral full width at half maximum of the amplified laser were 1037 nm and 11 nm respectively. Upon using a grating-pair for compression, 178 fs pulses with peak power of 14.2 GW were obtained. The beam quality factors measured of X-axis and Y-axis of the amplified laser were 1.09 and 1.17 respectively. To the best of our knowledge, this is the highest average power and the maximum pulse energy obtained from the Yb:CaYAlO4 amplifiers. For applications in high-repetition-rate attosecond light sources, terahertz generation and optical parametric amplification, subsequent laser outputs with an average power of 200 W, pulse energy of 20 mJ and pulse duration less than 200 fs are expected to be achieved by adding two stages of traveling-wave amplification.