Sub-40 fs Pulse Generation in a KTP-based Optical Parametric Oscillator

The demand for femtosecond sources at new wavelengths in the near to mid-infrared together with the emergence of the self-mode-locked Ti:sapphire laser as a convenient pump source has led recently to the development of femtosecond optical parametric oscillators. We report here the operation of a synchronously pumped femtosecond optical parametric oscillator (OPO) based on a 1.5 mm thick crystal of KTP cut for noncritical phase-matching. Pumped by 85 fs pulses from a self-modelocked Ti:sapphire laser the OPO is tunable over the bandwidth of the mirrors from 1.1 -1.3 μm and pump tuning over 100 nm is demonstrated. Our intracavity dispersion-compensated OPO has been operated in both three-mirror and four-mirror standing-wave geometries using single-pass pumping and exploiting a variety of mode-matching configurations. In addition, the observation of soliton generation in the femtosecond OPO is described. A typical spectrum and interferometric autocorrelation of the signal pulses produced in the three-mirror configuration are presented in Figure 1 and correspond to bandwidth-limited 39 fs pulses with intracavity peak powers approaching 1 MW [1]. The shortest pulses are observed when operating at near-zero intracavity GVD.