Highly-stable monolithic femtosecond Yb-fiber laser system based on photonic crystal fibers.

A self-starting, passively stabilized, monolithic all-polarization- maintaining femtosecond Yb-fiber master oscillator / power amplifier with very high operational and environmental stability is demonstrated. The system is based on the use of two different photonic crystal fibers. One is used in the oscillator cavity for dispersion balancing and nonlinear optical limiting, and another one is used for low-nonlinearity final pulse recompression. The chirped-pulse amplification and recompression of the 232-fs, 45-pJ/pulse oscillator output yields a final direct fiber-end delivery of 7.3-nJ energy pulses of around 297 fs duration. Our laser shows exceptional stability. No Q-switched modelocking events were detected during 4-days long observation. An average fluctuation of only 7.85 x 10(-4) over the mean output power was determined as a result of more than 6-hours long measurement. The laser is stable towards mechanical disturbances, and maintains stable modelocking in the temperature range of at least 10 - 40 (0)C.