Recent advances in tuneable
filters, which can select wavelengths rapidly through software
control, have rendered the time consuming bandpass
method largely obsolete. Acousto-optic Tuneable Filters
(AOTFs) and Liquid Crystal Tuneable Filters (LCTFs)
are the two most widely used tuneable filters in CI. AOTFs
have been used in the construction of commercially available
NIR-CI systems [24], while LCTFs show greater
promise for filtering of Raman images [22]. After spectral
encoding, an image of the sample at the selected wavelength
is recorded on a detector, which is usually a CCD
detector for Raman Imaging and an FPA for NIR Imaging.
Images at subsequent wavelengths are stacked to form
a hypercube and stored on a PC for further analysis.