Laser profile reshaping in a Fabry-Perot thin film

We report the observation of non-Gaussian reflected and transmitted laser spatial profiles resulting from the excitation of resonant modes below the critical angle for total reflection in a Fabry-Perot cavity formed by a thin ~7 um air film between two glass prisms. The observations of an interference minimum in the reflected profile and exponential decay in the transmitted profile are new and in excellent agreement with a complex pole theory. Extension of the theory to a larger ~0.7 m cavity at normal incidence predicts similar reshaped profiles.