Field-Resolved Infrared Spectroscopy using a Broadband Achromatic Interferometer

The concept of infrared electric-field resolved spectroscopy (FRS) involves the separation of the molecular response of the sample from an ultra-short excitation pulse in time, thereby decreasing the influence of technical noise on measurement sensitivity. It allows to reach a wider dynamic range for detection in comparison to time-integrating intensity measurement techniques such as Fourier-transform infrared (FTIR) spectroscopy [1]. We aim to extend this separation concept to the spatial domain, thereby reducing the residual effect of technical noise of the excitation in FRS further, extending the detection dynamic range and improving the ability of FRS to distinguish minute differences in the molecular constitution of biological samples. Differential molecular fingerprinting (dMF) is one such approach where the source excitation noise is cancelled through destructive interference between the two arms of an interferometer [2], [3]. When a sample is placed in one of the arms, its pure molecular response is observed in the destructive port of the interferometer which constitutes the differential signal, while the superposed source excitation is nullified (red and blue in Fig. 1a). In our experiment, we combined for the first time dMF with field resolved spectroscopy in the mid-infrared (MIR) region.