Monitoring of vapor uptake by refractive index and thickness measurements in thin films

We report a method for real-time monitoring of vapor uptake by simultaneous detection of the refractive index, n, and thickness, d, of thin transparent films with a precision of δn=10(-4) and δd<100 nm. The setup combines total internal reflection (Abbé) refractometry with an interferometric imaging method. A fast Fourier transform and phase fitting method is applied for accurate and independent determination of refractive indices and thicknesses. While the uptake of acetone vapor by polydimethylsiloxane is investigated, the system is also suited for characterization of other solid and liquid films.