We review the operating principles of noncollinear acousto-optic tunable filters (AOTF's), emphasizing the use of two orthogonally polarized beams for narrow-band imaging. Spectral characterization and spectral broadening measurements of commercially available AOTF's agree with theoretical predictions and reveal difficulties associated with imaging noncollimated light. An AOTF imaging spectropolarimeter for ground-based astronomy that uses CCD's has been constructed at NASA Goddard Space Flight Center. It uses a TeO(2) noncollinear AOTF and a simple optical relay assembly to produce side-by-side orthogonally polarized spectral images. We summarize the instrument design and initial performance tests. We include sample spectral images acquired at the Goddard Geophysical and Astronomical Observatory.
The purpose of this investigation is to improve the study of the characteristics of noncollinear acoustooptic tunable filters (AOTFs) used in imaging spectroscopy. Three filters were characterized and the results compared with tuning models to verify that device operation can be reliably predicted in advance. All these devices use tellurium dioxide as the interaction medium and have large geometric apertures for spectroscopic imaging applications in the spectral range 0.5-3.5 microm. The device characteristics that we studied were compared with the results of AOTF models, and the spectral and angular dependence of acoustic frequency and bandpass width for both output polarization states were confirmed by measurements. One of the AOTFs was used as a dispersive element coupled to external imaging optics. We summarize measurements of the basic spectral and imaging characteristics in this configuration.
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