Low-repetition-rate, high pulse energy all-polarization-maintaining Er-doped fiber laser mode-locked with a nonlinear amplifying loop mirror

We demonstrate a low repetition rate mode-locked Er-doped fiber laser using an all-polarization-maintaining (PM) nonlinear amplifying loop mirror. Stable single pulse generation had a pulse energy of 4 nJ and a repetition rate as low as 1.96 MHz. A section of standard single mode PM fiber was used to compress the output pulses from 2.5 ps down to 660 fs, being nearly transform-limited. The robust mode-locking design and all-PM cavity make this fiber laser stable and compact. The output average power fluctuation is within 0.17% over 10 h. Therefore, this source is ideally suitable for high pulse energy applications, such as micro-machining and nonlinear microscopy through further amplification.