Polymer Fabry-Pérot filters for organic solvent detection

We have fabricated Fabry-Pérot filters from standard optical polymers (polystyrene and poly-methylmethacrylate), chemically modified for allowing photo-crosslinking. The filter transmittance peak is at a wavelength of 600 nm, with a FWHM width of 20 nm. By adding organic solvents (acetone, toluene, THF) to the atmosphere surrounding the filter, the transmittance peak shifts up to 500 nm towards higher wavelengths. The physical basis for this is the diffusion of solvent molecules into the crosslinked polymer network, causing it to swell. This effect fast, reversible and (to first order) linear, therefore suggesting it as a novel spectroscopic principle for measuring gas concentrations.