Focusing characteristics of light beam passing through birefringent film

The properties of circularly polarized beams tightly focusing through a uniaxial crystal film are investigated by using the angular spectrum method of plane waves. The numerical results show that, for the positive crystal, the focus is closed to lens with the birefringence increasing. However, for the negative crystal, the focus shifts away from the lens and the size of the optical spot increases. With the increasing of the positive and negative crystal thickness, the focus is close to lens. However, the thickness of positive crystal increases the same as the thickness of negative crystal, the focus for the positive crystal film shifts more obviously than that for the negative crystal film. The closer the positive and negative crystal gets, the closer the focus is. When the film shifts rapidly, however, the intensity for the positive crystal film decreases more rapidly than that for the negative crystal film.