Electro-optic frequency comb and dual-comb spectroscopy using free-space ultrafast mid-IR modulators

This talk reports advances in free-space ultrafast mid-infrared modulators exploiting strong light–matter coupling. Operating at room temperature, these devices achieve > 80 % modulation contrast and -3 dB cutoff frequencies up to 15 GHz around 9 μm wavelength. When driven by short (~100 ps) electrical pulse trains, from a single or dual pulse generator, these modulators enable the generation of single- and dual “electro-optic” frequency combs. The accessible bandwidth is up to 20 GHz, with mode spacings down to 10 MHz (limited by the pulser). We perform a proof-of-concept dual-comb spectroscopy experiment using a single modulator and a single quantum cascade laser with a NH₃ cell and a Ge etalon. The results reveal that high-performance mid-IR modulators could be suitable for spectroscopy, frequency comb generation and, in the long term, spatial light modulation.