Dual-Oscillator Field-Resolved Infrared Spectroscopy with Individual-Scan Referencing

Field-resolved infrared spectroscopy (FRS) with electro-optic sampling (EOS) has evolved as a powerful alternative to conventional intensity-based infrared absorption measurements [1]. It allows to capture the response field of a molecular sample emitted upon vibrational excitation with an ultrashort infrared pulse, directly in the time domain. The temporal separation of excitation and molecular response enables background-free detection of the sample-specific signal via temporal filtering. In order to additionally reduce the influence of low- frequency noise of the mid-infrared (mid-IR) excitation, ultra-rapid EOS detection at multi-kHz scan rates has been implemented with mechanical [2] and dual-oscillator [3] approaches. Here, we present a dual-oscillator FRS instrument, recording broadband mid- IR EOS traces simultaneously in sample and reference channels, at a scan rate of 4.2 kHz. With full spectroscopic referencing on the individual-scan basis, the system can correct sample measurements for fast fluctuations and long-term drifts of the mid- IR excitation pulses.