High-Speed Fourier-Transform Infrared Spectroscopy with Phase-Controlled Delay Line

Fourier-transform infrared spectroscopy (FTIR) is the golden standard of mid-infrared (MIR) molecular spectroscopic analysis through optically encoded vibrational signatures. Michelson-type FTIR and MIR dual-comb spectrometers allow us to simultaneously investigate multiple molecular species via the broadband and high-resolution spectroscopic capabilities. However, these are not applicable to high-speed measurements due to the low temporal resolution which is fundamentally limited by the signal-to-noise ratio (SNR). In this study, a high-speed FTIR spectroscopy technique called phase-controlled Fourier-transform infrared spectroscopy (PC-FTIR) that has the capability to measure MIR absorption spectra at a rate of above 10 kHz is developed. PC-FTIR demonstrates the high scan rate with a high SNR for various spectral bandwidths by arbitrarily adjusting the instrumental spectral resolution. As a proof of principle demonstration, high-speed mixing dynamics of two liquids is measured at a rate of 24 kHz. MIR spectra of gas-phase molecules are also measured with higher spectral resolution at a rate of 12 kHz. This high-speed MIR spectrometer could be used especially for measuring non-repetitive fast phenomena and acquiring a large amount of spectral data within a short time.