1 MHz,273 W average power Ytterbium-doped rodtype fiber chirped pulse amplification system

Ytterbium-doped ultrafast fiber lasers are widely used in scientific research, industrial processing, medical diagnosis, and other fields due to their excellent beam quality and high output power. The larger mode area allows the fiber to deliver higher pulse peak power. The commercial rodtype Ytterbium-doped fiber with a core diameter of 85 μm produced by NKT in Denmark can produce ultra-short pulses of the order of 100 watts and 100 microjoules. Based on this rod-type fiber, we constructed a chirped-pulse amplification (CPA) system which uses high-efficiency transmission gratings and temperature-tunable chirped fiber Bragg grating (CFBG) to compensate for dispersion. We investigate the effect of input powers on the amplified power and pulse compression quality, and find that higher input power slows down gain saturation and improve amplification efficiency. At input powers of 20W and 30W, we obtained output powers of 305W and 323W respectively, with an amplification efficiency of about 80%. To reduce the accumulation of nonlinear phase shift, we employ circular polarization amplification. At low output powers (less than 160 W), the effect of nonlinear phase accumulation on the compressed pulse is negligible, and increasing the input power increases the amplification efficiency. When the output power exceeds 200 W, the increased accumulation of nonlinear phase shift degrades the pulse compression quality, which implies that the input power should be appropriately reduced to the power range between 5 W and 20 W. With an input power of 20W and a pump power of 429W, the output power can reach 305W. After pulse compression using a diffraction-grating pair, this rod-type fiber CPA system delivers 1 MHz, 264 fs pulses with 273 W average power. These results provide an important experimental basis for performance optimization of high-power and high-energy ultrafast fiber lasers.