Optical rectification of ultrafast Yb lasers: pushing power and bandwidth of terahertz generation in GaP

We demonstrate broadband high-power terahertz (THz) generation at megahertz repetition rates by optical rectification in GaP driven by an ultrafast Yb-based thin-disk laser (TDL) oscillator. We investigate the influence of pulse duration in the range of 50–220 fs and thickness of the GaP crystal on the THz generation. Optimization of these parameters with respect to the broadest spectral bandwidth yields a gap-less THz spectrum extending to nearly 7 THz. We further tailor the driving laser and the THz generation parameters for the highest average power, demonstrating 0.3 mW THz radiation with a spectrum extending to 5 THz. This was achieved using a 0.5 mm thick GaP crystal pumped with a 95 fs, 20 W TDL, operating at 48 MHz repetition rate. We also provide a simple method to estimate the THz spectrum, which can be used for design and optimization of similar THz systems.