Continuously tunable sub-ns ytterbium-doped MOPA system for frequency conversion

Our setup is based on supercontinuum source amplified by Yb-fiber amplifiers. The supercontinuum delivers 100 mW between 800 and 1300 nm with linearly polarized pulses of 900 ps, and a repetition rate of 20 kHz. Because of the low spectral power density of the supercontinuum, the system architecture is based on a dual-stage fiber amplifier to amplify the weak seed source. The tunability is achieved by means of an Acousto-Optic Tunable Filter (AOTF) with a filtering resolution of 10 nm. The diffracted beam is pre-amplified in a 5 m long Ytterbium Doped PM Double Clad fiber. For the power amplifier, pre-amplified pulses (~150 mW average power between 1040-1000nm) are coupled into a 1.2 m long Yb-doped Polarizing Double Clad fiber with a core diameter of 40 μm and cladding diameter of 200 μm backward pumped with a fiber coupled high-power laser diode of a 200 μm fiber (NA 0.22). The fundamental amplified laser beam is frequency converted in a SHG unit based on a 12 mm long critically phase-matched LBO.