Comb-resolved spectroscopy with immersion grating in long-wave infrared.

We have developed a dispersive spectrometer by using a compact immersion grating for direct frequency comb spectroscopy in the long-wave infrared region of 8-10 µm for the first time. A frequency resolution of 460 MHz is achieved, which is the highest reported in this wavelength region with a dispersive spectrometer. We also demonstrate individual comb mode-resolved imaging by cavity filtering and apply this to obtain spectra of both simple and complex molecular spectra. These results indicate that the immersion grating spectrometer offers the next advancement for sensitive, high-resolution spectroscopy of transient and large/complex molecules when combined with cavity enhancement and cooling techniques.