Synchronized, independently tunable fs light by pulsed optical parametric oscillators

We report on the generation of powerful, widely tunable fs radiation by parallel operation of two singly resonant optical parametric oscillators. The devices are synchronously pumped by the second harmonic of an additive-pulse modelocked Nd:glass laser, that provides pulse trains of ≈ 2.5 μs and 400 fs pulse duration. As nonlinear crystals in the OPO's we choose BBO specimens (length 5 mm and 5.8 mm, respectively), enabling generation of fs-pulses with further advantages of high damage threshold, high nonlinearity and good optical quality. Small differences of the experimental setup lead to slightly different OPO parameters. For OPO I a single pulse energy of 10 nJ is achieved in a tuning range of 0.9-1.5 μm with a pulse duration of 120 ± 20 fs while OPO II delivers pulses of 200 ± 20 fs in the range 0.7-1.5 μm. Frequency tuning of the OPO's is carried out within a fraction of a second by computer controlled stepping motors, readjusting crystal orientation, cavity length of the OPO and realignment of one resonator mirror. The time jitter is estimated from cross correlation measurements to be ±50 fs offering high temporal resolution in pump-probe investigations.