Spectral imaging in a programmable array microscope by hadamard transform fluorescence spectroscopy

We report the use of a thin-film transistor (TFT) twisted nematic liquid crystal spatial light modulator (SLM) for Hadamard transform two-dimensional spectral imaging in a fluorescence microscope. The liquid crystal SLM placed in the primary image plane of the microscope generates a set of spatial encoding masks defined by a cyclic S-matrix. The light passing through the mask is relayed by anamorphic optics to the entrance of an imaging spectrograph and detected with a charge-coupled device (CCD) camera. The SLM allows for the convenient generation of arbitrary masks without moving parts. The Hadamard transform approach transmits up to 50% of the light from the image field for multichannel detection, but is subject to transmission Losses in the SLM. The system allows the convenient acquisition of two-dimensional spectral images. We characterized and tested many of the parameters controlling both spatial and spectral resolution, and demonstrated the system in the analysis of both naturally fluorescing and stained biological samples.