Abstract

The THz region of the electromagnetic spectrum is of great interest for scientific and industrial applications since it enables non-destructive testing and thickness measurements of many materials that are opaque in the visible and infrared. Dual-comb lasers, which achieve rapid and precise optical delay scanning by emitting a pair of pulse trains with slightly different repetition rates, are an ideal solution to address these THz time domain spectroscopy (TDS) applications. Here we demonstrate THz-TDS with Fe-doped photoconductive antennas (PCAs) combined with a GHz Yb-CALGO single-cavity dual-comb laser. The laser, which is based on a spatial multiplexing technique to generate both combs in the same cavity [1], exhibits ultra-low free-running relative timing noise performance while emitting 77-fs pulses at 110 mW average power per comb centered at 1058 nm, at a repetition rate of 1.2 GHz and an adjustable repetition rate difference Δf_rep in the range [-175 kHz, 175 kHz]. With this laser we demonstrate several improvements over traditional THz-TDS systems: (a) fast update rates in the multi-kHz range, (b) reduced system complexity by using a free-running single-cavity dual-comb laser, (c) a favorable scan range of 0.85 ns, and (d) avoid pulse energy limitations of photoconductive antennas (PCAs) for THz generation.

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