We analyze the use of a film resonator in an angle-sensitive detector (ASD) for measuring very small deflections of a laser beam. A simple device consisting of a film resonator formed by a parallel air gap between two optical prisms is proposed. Quantitative modeling is done considering Gaussian laser beams. We present a detailed analysis of the sensitivity of the proposed ASD with respect to the beam’s size, resonator’s width, polarization, and prism refractive indices. An experimental verification of the proposed device is also presented. © 2003 Society of Photo-Optical Instrumentation Engineers.