12.7 mJ travelling-wave amplifier based on Yb:CALGO crystals at 1 kHz

In this paper, we demonstrate, for what we believe is the first time, a quasi-continuous-wave (QCW), one kilohertz, two-stage, double-pass travelling-wave amplifier based on Yb:CALGO crystals. A compact travelling-wave amplifier delivered an amplified pulse energy of 12.7 mJ at the central wavelength of 1038.1 nm. The amplified spectrum featured a full width at half maximum (FWHM) of 5.8 nm. Using a double-pass single-grating compressor, a pulse duration of 281 fs was measured. Owing to effective thermal management, the amplified laser beam profile exhibited a well-defined Gaussian distribution with a beam ellipticity of 0.92, corresponding to a beam quality factor (M 2 ) < 1.30 in each stage.