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Compact high-resolution spectrometer using two plane gratings with triple dispersion.

We demonstrate a compact high-resolution spectrometer scheme using two plane gratings. In this approach, the rays are first diffracted by a fixed grating, then incident on a rotating grating at the Littrow diffraction angle, and are finally diffracted and reflected back to the fixed grating again. Thus, triple dispersion (TD) occurs during measurement, increasing the resolution. The formulae of this compact high-resolution spectrometer are rigorously derived. A design simulation with two gratings of 1050 lines/mm is performed and discussed. In addition, a prototype of this spectrometer has been built and tested. Its spectral resolution reaches a precision of 36 pm.