| 摘要 |
PURPOSE:To realize economically and with simple constitution, for instance, the correction of a light beam that has astigmatism by setting each of the parameters so as to generate the astigmatism without any comatic aberration as a whole by providing at least two pieces of plane parallel plates in the luminous flux and making their thickness, refractive indices, and the angles the parameters. CONSTITUTION:In the optical path of the light beam generated by a light source 1 that passes an objective lens 2 and is irradiated on in a disc 3, an additional plane parallel plate 11 is inserted in addition to a plane parallel plate 4. The normal lines of the plates 4 and 11, and the optical axis are arranged to be approximately on the same plane, plus, the angle between the plate 4 and the optical axis, and that between the plate 11 and the axis are of approximately equal absolute values, but are of opposite signs. The magnitude of the astigmatism generated by the 2 plates is made to be decided by the three parameters of the thickness (t), refractive indices (n), and the angle of the normal line to the optical axis (absolute value) (theta). Therefore, the magnitude is controlled by setting these parameters in proper values. |
