Waist shift of a Gaussian beam by plane dielectric interfaces

This paper presents a theory on the shift of the waist position of a Gaussian beam due to plane dielectric interfaces. The waist shift is defined as the distance between the waist positions of the incident and transmitted beams. We derive it for the beam passing through a single or two plane interfaces and examine how it depends on the waist position of the incident beam and on the refractive indices of dielectrics. The condition for locating the waist of the transmitted beam at a prescribed position is also clarified.