We numerically and experimentally demonstrate a Yb-doped fiber ultrashort pulse generator based on self-phase modulation and alternating spectral filtering, operating at a wavelength of 1060 nm and providing a stable ultrashort pulse train. Pulses with energy up to 2.8 nJ were generated experimentally and were limited only by available pump power.

Results of numerical and experimental investigations of the simple fiber CPA system seeded by nearly bandwidth-limited pulses from the picosecond oscillator are presented. We utilized self-phase modulation in a stretcher fiber to broaden the pulse spectrum and dispersion of the fiber to stretch pulses in time. During amplification in the ytterbium-doped CCC fiber, gain-shaping and self-phase modulation effects were observed, which improved pulse compression with a bulk diffraction grating compressor. After compression with spectral filtering, pulses with the duration of 400 fs and energy as high as 50 µJ were achieved, and the output beam quality was nearly diffraction-limited.

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We demonstrate an efficient technique for the second harmonic generation (SHG) of the broadband radiation based on the temperature gradient along a nonlinear crystal. The characteristics of Type I non-critical phase-matched SHG of broadband radiation in the LiB(3)O(5) (LBO) crystal with the temperature gradient imposed along the crystal were investigated both numerically and experimentally. The frequency doubling efficiency of the broadband pulsed fiber laser radiation as high as 68% has been demonstrated.

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