Optical design of an imaging spectrometer utilizing an acousto-optic tunable filter as a disperser

Designing an imaging spectrometer using an AOTF can be a difficult task since there is no software that can simulate the bulk diffraction that takes place in the AOTF material. In this paper we will describe the method used to simulate the effects of the AOTF using a refractive grating halfway along the crystal. Apart from the zero order we also collect the +1 and -1 orthogonally polarized orders produced by the AOTF, gaining additional information that may be used in certain applications. The +1 and -1 order are imaged into the same focal plane, eliminating the need of a separate focal plane for each order and resulting in considerable savings in cost and mass. The whole system is achromatized from 1.2 - 2.4 microns using only two types of glass, one of which is BK7. The system has been designed, built, and tested.