Cryogenically cooled yb: KGW regenerative amplifie

We develop a diode-pumped cryogenically cooled Yb: KGd(WO 4 ) 2 (Yb: KGW) crystal regenerative amplifier (RA). At 77 K, it delivers 1.28 mJ output pulses with 2.9 nm spectral bandwidth and output power stability of 0.7% at a 1 kHz repetition rate. The amplified beam demonstrates near-diffraction-limited quality, exhibiting M² factors of 1.01 and 1.01 in the horizontal and vertical directions, respectively. To our best knowledge, this is the first cryogenically cooled Yb: KGW crystal RA.