THz Power Scaling Up to 1.6 Mw in Fiber-Coupled ASOPS THz TDS with a 1 GHz Dual-Comb Laser

Fiber-coupled terahertz (THz) time-domain spectroscopy (TDS) systems often employ photoconductive antennas (PCAs) as THz emitters due to their high IR-to-THz conversion efficiency. However, their THz power has been constrained to about 1 mW, as fiber-based pulse delivery limits the excitation power to under 60 mW at typical fiber laser repetition rates around 100 MHz. Here, we report the first THz TDS setup that overcomes this limitation by operating at an elevated repetition rate of 1 GHz. We show that the conversion efficiency of InGaAs:Rh-based PCAs is preserved at this one-order-of-magnitude higher repetition rate, resulting in a record emitted THz power of 1.58 ± 0.08 mW for fiber-coupled THz emitters. This significant improvement is enabled by an ultrafast dual-comb optical parametric oscillator operating at 1 GHz repetition rate, delivering two trains of 200 fs pulses centered at 1.55 μm wavelength with up to 650 mW average power. Further pulse compression to 86 fs is achieved using a 2.6 m long fiber delivery to the PCAs, combining dispersion-compensating and standard polarization-maintaining fibers. Using this setup, we demonstrate THz TDS utilizing asynchronous optical sampling at a scan rate of 414 Hz with a peak dynamic range of up to 92 dB at 20 GHz frequency resolution, and 79 dB at 1.1 GHz frequency resolution in 113 seconds integration time.