The pump source starts with a customized Yb-fiber laser (Yacto, YF-FL-50-100-IR) emitting 1030 nm pulses with a duration of 260 fs at 500 kHz repetition rate. A small fraction of pulse energy ~8 μJ is focused into a 15-mm-long YAG crystal generating a stable white light spanning from 1.1 to 1.9 μm in the near-infrared region. An 8-mm-long anti-reflection coated KTP crystal cut at θ = 44.5°, φ = 0° for type II PM is used in the OPA. The idler wavelength is tunable from 2.4 to 2.8 μm by twisting the PM angle. The output power of the idler wave is measured up to 500 mW by using a 15 W pump. The pulse duration of idler wave is characterized as 320 fs with some uncompensated dispersion inherited from the OPA system, through a home-built interferometer autocorrelator.
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