Highly efficient optical parametric chirped-pulse amplification based on BiB3O6 and β-BaB2O4 crystals at low pump intensity

► We measured the gain characteristics of two important nonlinear crystals, BiBO and BBO. ► We report a very high signal gain in a two-stage OPCPA using both BiBO and BBO. ► A signal gain of 1.13 × 107 was obtained at a low pump intensity of 260 MW/cm2. ► This signal gain is the highest at low pump intensities less than 300 MW/cm2.