We report on an investigation of a passively mode-locked picosecond ytterbium-doped fiber laser with a repetition rate close to 1 MHz. The mode-locking operation was induced by a butt-coupled semiconductor saturable absorber mirror (SESAM) and stabilized in the normal dispersion regime by means of spectral filtering of a narrow bandwidth (0.1 nm) fiber Bragg grating (FBG). A pulse duration of about 50 ps with maximum output power of 20 mW at 1064 nm were achieved after amplification in the double-pass fiber preamplifier. This compact and reliable all-fiber laser operating at 1064 nm is intended to seed bulk amplifiers in a hybrid fiber/solid-state configuration. Employing a two-stage Nd:YVO4 amplifier, we obtained 10 W average output power, which preserved both the quasi-diffraction limited beam quality and spectral purity of the seeder. Second harmonic generation (SHG) with 50% conversion efficiency was demonstrated in type-II potassium titanyl phosphate (KTP) and type-I angle phase matched lithium triborate (LBO) crystal. Furthermore, a space independent numerical model was developed in order to study the dependence of intracavity pulse energy on the main design parameters of the master oscillator (cavity length, FBG bandwidth, SESAM modulation depth) within the stability range (single pulse per round trip in CW mode-locking operation) of the fiber laser master oscillator.
© 2013 Optical Society of AmericaPDF Article