Deviation from Snell's law for beams transmitted near the critical angle: application to microcavity lasers.

We show that when a narrow beam is incident upon a dielectric interface near the critical angle for total internal reflection it will be transmitted into the far field with an angular deflection from the direction predicted by Snell's law, because of a phenomenon that we call "Fresnel filtering." This effect can be quite large for the parameter range that is relevant to dielectric microcavity lasers.