Field-Resolved Sample-Modulation Spectroscopy for Mid-Infrared Molecular Fingerprinting

Field-resolved infrared spectroscopy by electro-optic sampling (EOS) provides exceptional dynamic range and sensitivity, with promising applications in biomedical analysis [1], [2]. The current limitation in achievable spectroscopic sensitivity is given by laser fluctuations and drifts during the duration of a measurement. Recently, the acquisition time for a single EOS scan could be reduced to the sub-millisecond regime by introducing modulated dual-oscillator scanning with precise delay calibration [3]. This approach allows to effectively “freeze” low-frequency laser noise. However, quantitative spectroscopic studies typically require a comparison between sample and reference measurement. For liquids, the necessary sample exchange leads to durations of the measurement cycle on the order of 10s of seconds, during which laser drifts accumulate. Here, we show that combining kHz-rate dual-oscillator EOS scanning with Hertz-rate sample-exchange modulation allows to remove the influence of slow laser drifts on spectroscopic comparison measurements.