Pulse compression in a mid-infrared synchronously pumped optical parametric oscillator.

摘要

Short pulse tunable sources in the mid-infrared optical region have been an indispensible tool of research for several years. Yet the complexity of these systems limits their usefulness in many applications. In this study, pulse compression in a synchronously pumped optical parametric oscillator (SPOPO) is investigated as an alternative to these systems. Although pulse compression has been known for several years, a full understanding of the process has not been developed. This has inhibited its full exploitation. In this work, a search of the input parameter space is conducted in order to illucidate the mechanisms involved in pulse compression. The experiments conducted correlated compression to the input energy, optical parametric oscillator (OPO) wavelengths, and OPO cavity length detuning. The 10 ps pump pulses from a pulsed Nd:YAG laser interact in the parametric oscillator to generate infrared output pulses as short as 400 fs---a 20 fold compression. Experiments indicate that the compression varies directly with the input energy and inversely with the signal-idler group velocity mismatch (GVM) across the 2.5--4.0mum spectral range. It is also found that the cavity detuning length affected the dynamics of the nonlinear interaction.{09}To gain physical insight into the experimental findings, numerical modeling is employed. Using nominal values for the input parameters, it is found that the model predicts the compression within about 30% and accurately predicts the input energy and signal-idler GVM trends. This agreement is then the basis for employing the model to extract physical insight into the compression mechanism. The dependence of compression on the signal-idler GVM is found to be more than an order of magnitude stronger than the signal-pump GVM usually thought to be responsible for the pulse compression. The model further predicts that using a 1 ps pump source should yield pulses on the order of 50 fs and that strong pulse compression could also be observed in other mid-infrared nonlinear crystals. Additionally the model is used to investigate the limits of compression with respect to increasing input energy and decreasing signal-idler GVM.