Rapid mechanical scanning at 8 kHz for in-flow mid-IR field-resolved spectroscopy

High-speed vibrational spectroscopy is a sensitive label-free approach for molecular fingerprinting in dynamic and non-repetitive systems. Field-resolved mid-IR spectroscopy based on electro-optic sampling (EOS) offers broad bandwidth and high dynamic range, but reducing the technical complexity of high-speed implementations remains challenging. Here, we demonstrate the use of a galvanometer scanner resonant at 4 kHz for high-speed EOS of mid-IR pulses with a single-scan acquisition time of 125 μs. Interferometric delay tracking and reconstruction provide femtosecond-level timing precision and spectra compatible with those of conventional slow-scan, lock-in measurements. We validate the operational functionality of the EOS resonant scanner by monitoring dimethyl sulfone concentration in water in a flow-through cuvette in real time. This approach offers advantages in reducing technical complexity, improving cost-effectiveness, and enabling flexible selection of the scanning speed.