Broadband THz-TDS with 5.6 mW average power at 540 kHz using organic crystal BNA

We demonstrate efficient optical rectification in the organic crystal BNA (N-benzyl-2-methyl-4-nitroaniline), driven by a temporally compressed, commercially available industrial Yb-laser system operating at 540 kHz repetition rate. Our THz source reaches 5.6 mW of THz average power driven by 4.7 W, 45 fs pulses and the resulting THz-TDS combines a very broad bandwidth of 7.5 THz and a high dynamic range of 75 dB (in a measurement time of 70 s). The conversion efficiency at maximum THz power is 0.12%. To the best of our knowledge, this is the highest THz power so far demonstrated with BNA, achieved at a high repetition rate, and enabling to demonstrate a unique combination of bandwidth and dynamic range for THz-spectroscopy applications.