We report a very high signal gain of 1.13 × 10 7 at a low pump intensity of 260 MW/cm 2 in a two-stage optical parametric chirped-pulse amplifier (OPCPA), which is used as a pre-amplifier for a short-pulse front-end Nd: glass high-energy laser system. A signal energy of 0.17 nJ was amplified to 2 mJ with a central wavelength of 1053 nm and a repetition rate of 10 Hz using the OPCPA with a 15 mm-long BBO crystal at optical parametric amplifier (OPA) stage 1 and a 12 mm-long BiBO crystal at OPA stage 2.
