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

Abstract

Abstract 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.