All-normal-dispersion figure-8 and figure-9 femtosecond Yb-doped fiber lasers

The applications of femtosecond lasers are undergoing a period of explosive growth in the laser micromachining market. We demonstrated an all-normal-dispersion figure-8 mode-locked fiber oscillator using a nonlinear amplifying loop mirror, delivering laser pulses with 8.2-nJ pulse energy. The spectral bandwidth of 10 nm is realized at the repetition rate of 10 MHz. The pulse width of the chirped pulses is 6.7 ps and the output pulses can be compressed to below 200 fs. An all-normal-dispersion figure-9 laser is also presented in this letter. The repetition rate of the laser can be improved to 25.7 MHz. Owing to their compact sizes, high stability and superior self-starting ability, the all-normal-dispersion figure-8 and figure-9 lasers have the potential to be used in industrial grade femtosecond laser systems.