Direct Frequency Comb Spectroscopy with an Immersion Grating

Direct frequency comb spectroscopy (DFCS) in the mid-infrared region, especially in the long mid-infrared region (>5 μm), is a powerful technique for atmospheric remote sensing [1] and fundamental spectroscopy such as studies of C 60 [2]. DFCS has been demonstrated in Fourier transform spectroscopy, dual-comb spectroscopy, and techniques involving a dispersive spectrometer. Although a dispersive spectrometer with a virtually-imaged phase array (VIPA) can probe transient molecules by recording spectra within 10 μs [3,4], it has the disadvantages of low throughput and limited-bandwidth, which present challenges for sensitive, broadband detection at high time resolution.