1 kHz, 10 mJ Yb:CaGdAlO₄ Amplifier

High energy femtosecond laser systems provide the experimental basis for pumping variety of optical processes, ranging from high harmonics, terahertz science, and optical parametric amplification. [1], [2]. Yb:CaGdAlO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>, serving as a host laser crystal, has emerged as an especially suitable option for high energy, short pulse amplifier. It features a remarkably smooth and broad gain bandwidth of 70 nm with a flat-top shape for cr-polarization[3]. This unique characteristic not only enables a reduction in gain narrowing effects but also contributes to high energy output. In this paper, we reported a pulsed pump, two-stage, dual-pass Yb:CaGdAlO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> amplifier. The front seed is a 1 kHz, 6.5 mJ Yb:CaGdAlO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> dual-crystal regenerative amplifier. In the first stage, a two-pass amplifier is employed to suppress self-oscillation, The mode diameters of the seed and the pump are both 540 μm. In the case of the double-pass configuration without pumping, the seed laser has 5.56 mJ remaining after reabsorption loss. At a pump power of 250 W with a pump duty cycle of approximately 42%, it has been achieved that the pulse energy reaches up to 9.9 mJ, the laser beam ellipse is greater than 0.9. In the second stage, the mode diameter of the seed and pump laser on the Yb:CaGdAlO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> crystal are 600 μm and 540 μm. It is also pumped by a quasi-continuous pump with a pump duty cycle of approximately 42%. This pumping mechanism offers sufficient amplification. As a result, when seeded with the 7 -mJ output from the first stage, the amplifier can extract 10.8 mJ of energy with pump power at 250 W. The spectrum of 10.8 mJ was centered at 1039 nm and show a full width at half maximum of 6.2 nm. Using a double-pass, Single-grating compressor, the pulses can be compressed to 310 fs.