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.
In this paper, we introduce a detailed study of degradation of the In x Ga 1-x As quantum well (QW) based semiconductor saturable absorber mirror (SESAM) irradiated with picosecond pulses from a fiber laser at a 1064 nm wavelength. In a slow degradation study at a lower incident fluence, the longest operating times of ~4000 h were recorded for two SESAMs with a slow carrier relaxation (τ = 15 ps) in comparison to 1000 h of the fast (τ = 1 ps) SESAM. The nonlinear reflectivity measurements after the long-term tests indicated that the most likely mechanism of SESAM degradation was the modification of the InGaAs QW structure. By reducing a thermal load on the SESAM, an expected lifetime was increased tenfold. At higher saturation levels, SESAMs experienced critical optical damage (COD) after less than 24 h of operation. The most likely mechanism of COD was deduced to be the two-photon absorption in GaAs material. The necessity of slow degradation tests close to the operating conditions of the SESAM was demonstrated.
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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