| 摘要 |
PROBLEM TO BE SOLVED: To provide a phase modulation element capable of reducing beam incident angle dependency of phase modulation characteristics.SOLUTION: A phase modulation element PM is arranged on an optical path with which beams consisting of diffused light or convergent light pass, and includes: a phase modulation area A; and a non-phase modulation area B. The phase modulation element PM has: a first surface R1; and a second surface R2 on its rear side. The first surface R1 is a concave conical surface, and the second surface R2 is a convex conical surface. An element shape of the phase modulation element PM is an axicon type element shape in which the first surface R1 and the second surface R2 are axial symmetric to a light axis AX on any cross section including the light axis AX and along a direction of the light axis AX. When the diffused light is made incident on the phase modulation element PM, the first surface R1 becomes an incident surface, and the second surface R2 becomes an emission surface. On the other hand, when the convergent light is made incident on the phase modulation element PM, the second surface R2 becomes the incident surface, and a second surface R1 becomes the emission surface. |
