Compact acousto-optic imaging spectro-polarimeter for mineralogical investigations in the near infrared.

Abstract

Spectral imaging in the near infrared is a promising method for mineralogy analysis, in particular well-suited for airless celestial objects or those with faint atmospheres. Additional information about structure and composition of minerals can be obtained using spectral polarimetry with high spatial resolution. We report design and performance of laboratory prototype for a compact near infrared acousto-optic imaging spectro-polarimeter, which may be implemented for remote or close-up analysis of planetary surfaces. The prototype features telecentric optics, apochromatic design over the bandwidth of 0.8-1.75 µm, and simultaneous imaging of two orthogonal linear polarizations of the same scene with a single FPA detector. When validating the scheme, reflectance spectra of several minerals were measured with the spectral resolution of 100 cm-1 (10 nm passband at 1 µm). When imaging samples, the spatial resolution of 0.6 mm at the target distance of one meter was reached. It corresponds to 100 by 100 diffraction-limited elements resolved at the focal plane array (FPA) for each of the two light polarizations. A similar prototype is also being designed for the spectral range from 1.7 to 3.5 µm. This type of the spectro-polarimeter is considered as a potential reconnaissance and analysis tool for future planetary or moon landers and rovers.