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An all-fiber optical laser pulse multi-pass stretcher using a chirped fiber Bragg grating (CFBG) is demonstrated. Pulses from a 1 053-nm mode-locked fiber seed oscillator are stretched by multiple passing through a chirped fiber grating set in a fiber regenerative amplifier structure. We stretch the pulse from 16 ps to 1.855 ns after it transmits seven loops in the stretcher. The main factors that affect the stretching results are discussed.

A fiber-based precision synchronization triggering system using fiber pulse stacker combined with high-speed electronics processing technology is presented. The relative timing jitter between two laser pulses achieved with this system is 4.09 ps (rms) in 2 h. The impact of the optical pulse amplitude fluctuation on the timing jitter is effectively reduced by high-speed analog-digital conversion and the reliability of the synchronization measurement system is confirmed.

An all-fiber regenerative amplifier at 1053 nm is demonstrated. The input signal pulse energy is 75 pJ in a 3.5-ns pulse at a 1-Hz repetition rate. At a low level of input pump power of 110 mW, the saturated output energy is 120 nJ with fluctuation less than 2% root mean square (RMS) even the fluctuation of the input pulse be about 15% (RMS). And the signal-to-noise ratio (SNR) is 66 dB. Maximum output energy of 780 nJ with a total gain of more than 40 dB is obtained at pump power of 130 mW. Scaling to higher pulse energy is constrained by stimulated Raman scattering. OCIS codes: 060.2320, 140.3280. doi: 10.3788/COL201210.S20610. As one of the most important components of a highpower laser system, the front end system seeds the subsequent laser system with pulses that have high stability, high beam quality, proper bandwidth, and high signalto-noise ratio (SNR). The output quality of front end determines the output quality of the whole laser system to a large extent. So developing a high-gain and high output stability amplifier with superior beam quality is attractive and important. Fiber optical amplifiers based on rare-earth-doped fibers have been investigated for decades [1 3] because of their inherent compactness, superior beam quality, and stability. Optical pulses with high repetition rate are routinely amplified by one or more staged single-pass rareearth-doped fiber amplifiers. However, the front end of high-power laser system runs in the state of extremely low repetition rate. The low-duty-cycle pulses leave large population inversion in the gain fiber for long durations between pulses, which can lead to serious broadband amplified spontaneous emission (ASE). The ASE competed for the unsaturated gain restricts the gain and degrade the SNR [4] .

We report the generation of an 8.5-nJ chirped pulse from a mode-locked all-fiber Yb-doped laser. Mode-locking is achieved through nonlinear polarization evolution (NPE) along with spectral filtering. The laser delivers 135 mW of average output power with positively chirped 10.9-ps pulses. The pulse repetition rate is 15.9 MHz, which results in an energy of 8.5 nJ per pulse. The externally dechirped pulse duration is 223 fs, and the pulse energy is 6 nJ, which corresponds to the peak power of ~27 kW.