THz Characterization and Generation of Temperature-Controlled Organic Crystal BNA

THz time domain spectroscopy (THz-TDS) based on nonlinear conversion and detection in $\chi^{(2)}$ crystals is well-established in the scientific community and is also increasingly adopted in industrial scenarios. In this context, organic crystals are an increasingly popular choice to generate THz radiation with large bandwidth and high conversion efficiency. One commonly accepted compromise to make is that their poor thermal properties results in damage and low average power tolerance. Nevertheless, it was recently shown that organic crystals are suitable under carefully controlled conditions for pumping with high-power, Yb-based laser sources operating at 1030-nm using HMQ-TMS and BNA [1]–[3]. However, to the best of our knowledge no attempt was made so far to actively temperature-control the crystals as a path to improve their thermal properties and enable stronger pumping powers; additionally, there was no report of temperature-dependent properties of these crystals. In this paper, we present both THz generation experiments using actively-cooled BNA in combination with a high-average power 1030 nm Yb-based fs-laser and present temperature-dependent (80K - 300K) refractive index and absorption data for BNA for the first time. Our data shows increased THz field strength (+25%), clearly corresponding to a reduced THz absorption at low temperatures, providing one important ingredient for future optimization of high-power broadband THz sources.