Constant-dispersion grism spectrometer for channeled spectra

A new spectrometer design is presented in which the angular dispersion with respect to wave number is nearly constant. The spectrometer is a type of grism, a series combination of grating and prism, in which the constant parts of the dispersion terms add to one another but the slopes of the dispersions tend to cancel one another. A systematic method is presented for optimizing the grating and prism parameters. A cross-dispersion technique is presented, eliminating overlapping grating orders. A design example is given for the visible region from 0.45 to 0.80 micron with essentially constant wave-number dispersion and a peak transmission of approximately 95 percent. This grism is well suited for measuring channeled spectra as generated by an optical stellar interferometer.