Based on the birefringence performance of YVO4, a Beam Displacer can divide a beam into o-rays and e-rays. When a natural beam transmits through a birefringent crystal, the beam divides into two rays. One ray transmits through the crystal in a strait path, this ray is called the ordinary ray (o-ray). the other ray is transmitted through the crystal, but changes its direction. This ray is called the extraordinary ray (e-ray). The angle between the o-ray and the e-ray is called the walk off angle α. It is given by:
α = tg-1( no2/ne2 * tgθ )-θ
θ is the angle between the light beam and the optical axis
