摘要： 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 and fundamental spectroscopy such as studies of C60. 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, it has the disadvantages of low throughput and limited-bandwidth, which present challenges for sensitive, broadband detection at high time resolution. In this work, we overcame the challenges of a VIPA spectrometer by developing a direct frequency comb spectrometer in the 8.5 μm region using an immersion grating. A preliminary demonstration was reported at 4 μm in this conference two years ago. The spectrometer provides the capability to perform precise spectroscopy of transient and large molecules in the long mid-infrared region.