Analysis of three-dimensional interference patterns of an inclined capillary

We study the interference patterns from an inclined capillary tube filled with liquid by using the ray tracing method and interference theory. A beautiful elliptical pattern is found on the screen, with refined fringes embedded in it. Particularly, the fringes on top of the pattern are continuously swallowed to the center with the angle of incidence increasing. In addition, a method is demonstrated to determine the refractive index of the liquid and the wavelength of the incident light by measuring the capillary tilt of every 10-fringe being swallowed, which looks like fringe crossover, with respect to the change of the inclined angle of the capillary.