Fourier transform spectroscopy in the vibrational fingerprint region with a birefringent interferometer

We introduce a birefringent interferometer for Fourier transform (FT) spectroscopy in the mid-infrared, covering the vibrational fingerprint region (5-10 mu m, 1000-2000 cm(-1)), which is crucial for molecular identification. Our interferometer employs the crystal calomel (Hg2Cl2), which combines high birefringence (n(e)-n(o)approximate to 0.55) with a broad transparency range (0.38-20 mu m). We adopt a design based on birefringent wedges, which is simple and compact and guarantees excellent delay accuracy and long-term stability. We demonstrate FTIR spectroscopy, with a frequency resolution of 3 cm(-1), as well as two-dimensional IR (2DIR) spectroscopy. Our setup can be extended to other spectroscopic modalities such as vibrational circular dichroism and step-scan FT spectroscopy. (C) 2017 Optical Society of America