Spectrotemporal dynamics of a picosecond OPO based on chirped quasi-phase-matching

We report on the first experimental investigation of the spectral dynamics of a synchronously pumped optical parametric oscillator (OPO) by use of dispersive Fourier transformation. For standard pumping rates, we observe a reproducible steady-state pulse-to-pulse spectrum. However, at high pumping levels, the OPO delivers pulse trains with nontrivial oscillatory spectral patterns. So as to benefit from a tailored broadband gain spectrum, the investigated OPO contains a chirped quasi-phase matching (QPM) nonlinear crystal. We explore the specific impacts of using such a remarkable parametric amplification medium where nonlinearly coupled frequencies vary with position. Depending on the QPM chirp rate sign, a red- or blue-shift of the emitted wavelength occurs when the OPO is switched on, leading to different spectral steady-states. These singular spectrotemporal dynamics are evidenced and explained for the first time.