Ultrabroadband phase-matching optical-parametric chirped-pulse amplification with a diverged pump beam

Akahane, Yutaka; Ogawa, Kanade; Aoyama, Makoto; Harimoto, Tetsuo*; Yamakawa, Koichi

We have demonstrated ultrabroadband optical-parametric chirped-pulse amplification around 1000 nm wavelength with diverged pump beam. In experiment, seed signal pulse with over 400 nm bandwidth and about 1 ps duration, which was broadened by photonic-crystal fiber, and pump pulse with 510 nm center wavelength, 1.1 ps duration and 1 mJ energy, which was generated by cryogenically-cooled Yb:YLF pump laser were overlapped in BBO crystal with 1.2 deg internal crossing angle. The divergence of the pump beam was adjusted by a pair of collimating lenses (f1 = +560 nn, f2 = -560 mm) inserted before BBO crystal. With 1.6 mrad divergence of pump beam, we have observed 400 nm ultrabroadband amplified signal, which is twice of our previous OPCPA experiment with collimated pump beam. Parametric gain with 76 GW/cm was measured as high as 1.210 in this experiment, which is sufficient for intense few-cycle laser pulse generation with this scheme.