Precision thickness and refractive index imaging of molecular films

Abstract

We present an interferometric contrasting technique that allows visualizing the thickness and refractive index of a molecular film being part of an optical multilayer structure (etalon). Small wavelength shifts of the comblike etalon spectrum are transformed into measurable intensity variations using a second reference etalon (optical correlator), illuminated in series. A charge-coupled device camera acting as two-dimensional photometer is utilized to measure the optical spectral correlation (OSC) image. The performance of the here proposed optical spectral correlation method is demonstrated using very thin confined liquid films. We give a detailed signal-to-noise analysis. Subangstrom film thickness resolution is experimentally verified with single exposure images acquired at frame rates comparable to video standards (approximately 25 Hz). Finally, we describe the calibration procedures necessary to obtain an absolute quantification of the OSC image.