Spectropolarimetric Imaging of Laser-Induced Fluorescence

A compact wavelength and polarization agile acoustooptic tunable filter (AOTF)-based imager is used to obtain both spectral and polarization signatures from laser-induced fluorescence in a solution for the first time. This imager covers the visible to near-IR region from 400 to 800 nm, with a 10-nm spectral resolution at 600 nm, it uses an electronically tunable TeO ₂ AOTF as a bandpass filter, and a nematic liquid crystal variable retarder to change polarization to obtain two orthogonally polarized images at each spectral wavelength. In this experiment, a blocking filter for the laser was not used before the camera. Here we present fluorescence measurement results for a dilute solution of fluorescein in acetone, using a 532-nm laser. Our results showed that for the vertically polarized exciting light, the fluorescence has a spectropolarimetric dependence in agreement with literature. This imager provides a simpler yet powerful tool to facilitate such measurements remotely with ability to extract both spectral and polarization information at each pixel of an extended sample image.