Abstract
AbstractFourier‐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.
Highlights
Fourier-transform infrared spectroscopy (FTIR) has been widely used in a variety of fields as a simple and robust tool for label-free molecular analysis
We develop 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
Dual-comb spectroscopy (DCS) with two mutually coherent frequency combs based on the MIR laser sources significantly improved the frequency accuracy and spectral resolution down to ~100 MHz (~0.003 cm-1) [6,7,8,9,10], benefiting precision molecular analysis
Summary
Fourier-transform infrared spectroscopy (FTIR) has been widely used in a variety of fields as a simple and robust tool for label-free molecular analysis. To obtain a high SNR within a short measurement time, reducing spectral resolution and/or bandwidth is required according to the above-mentioned trade-off relation One approach for this is DCS with MIR comb sources with higher repetition rates of ~10 GHz - ~100 GHz (which corresponds to instrumental spectral resolutions of ~0.3 cm-1 - ~3 cm-1) such as quantum cascade lasers [16], interband-cascade lasers [17], micro-resonators [18] and electro-optic modulators[19]. Demonstrations of MIR-DCS with those frequency comb sources have shown the scan rate of up to about 1 MHz [20,21,22] and used for measuring fast phenomena such as protein reactions [23], liquid flow [24] and hightemperature gaseous reaction [25] with their high temporal resolution These DCS spectrometers are promising approaches, they require exotic comb sources with limitations imposed by the low pulse energy, limited spectral tunability, and/or low spectral flatness. We measure gas-phase molecular absorption with a higher spectral resolution and relatively narrower MIR spectra at a spectral acquisition rate of 12 kHz by adjusting the spectral resolution and bandwidth to keep the high SNR (measurement time)
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