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Cavity-enhanced measurements for determining dielectric membrane thickness and complex index of refraction



Corey A. Stambaugh, Utku Kemiktarak, Mathieu Durand, John R. Lawall


The material properties of silicon nitride play an important role in the performance of SIN membranes used in opto-mechanical setups. Accurate modeling of the reflectivities of sub-wavelength diffraction gratings is especially dependent on knowledge of the complex index of refraction. Here we describe a cavity enhanced method to measure the complex index of refraction along with the material thickness of dielectric samples with small, but non-zero absorption coefficients. The method relies on the enhanced sensitivity of the cavity optics to a dieletric film inserted into the cavity. By determining Brewster's angle and a second interference angle, both the real part of the index and thickness can be measured, while measurements of the losses in the empty cavity and cavity with dielectric provide a measurement of the absorption of the dielectric.
Applied Optics


thin film, absorption, silicon nitride, optics, cavity, index of refraction
Created July 23, 2014, Updated November 10, 2018