Fixed-polarizer ellipsometry: a simple technique to measure the thickness of very thin films

The fixed-polarizer ellipsometer measures thickness of thin films. It is simple, inexpensive, and provides a linear response over a range of 800 A. We develop a matrix formulation to describe the optical characteristics of the instrument and apply it to the case of a single thin film on a substrate. Excellent agreement is found between experimental and simulated results. Applying the instrument to optical immunoassay, we show that its sensitivity can extend to 4 pg/ml, depending upon the analyte. This compares favorably with commercially available manual and automated immunoassay systems. The fixed-polarizer ellipsometer appears to be well-suited for use in laboratory and production environ- ments.