  We demonstrate a compact watt-level all polarization-maintaining (PM)
femtosecond fiber laser source at 1100 nm. The fiber laser source is seeded by
an all PM fiber mode-locked laser employing a nonlinear amplifying loop mirror.
The seed laser can generate stable pulses at a fundamental repetition rate of
40.71 MHz with a signal-to-noise rate of >100 dB and an integrated relative
intensity noise of only ~0.061%. After two-stage external amplification and
pulse compression, an output power of ~1.47 W (corresponding to a pulse energy
of ~36.1 nJ) and a pulse duration of ~251 fs are obtained. The 1100 nm
femtosecond fiber laser is then employed as the excitation light source for
multicolor multi-photon fluorescence microscopy of Chinese hamster ovary (CHO)
cells stably expressing red fluorescent proteins.
