A Prototype Slitless Spectrograph with a Composite Grism

We report the results of laboratory studies of the main optical properties of the slitless spectrograph developed for a small telescope with a 0.5 m-diameter primary mirror and a focal ratio of \(1:6.8\). The spectrograph operates in the 450–950 nm wavelength interval and has a field of \(35\overset{\prime}{.}6\times 7\overset{\prime}{.}2\). Its distinctive feature is the use of a composite grism subdivided into two subapertures with independently optimized parameters. Measurements show that the use of such a grism makes it possible to achieve a spectral resolving power \(R\) from 461 to 1041 with the grating diffraction efficiency as high as 45\(\%\). We demonstrate that our solution provides better optical characteristics compared to the classical grism and that our measurements agree well with the results of modeling.