| 摘要 |
PROBLEM TO BE SOLVED: To provide a transmission type polarization retardation plate which is easy to manufacture and has small transmitted light quantity loss of far-infrared light, and to provide a laser beam machine using the same.SOLUTION: A polarization retardation plate 100: is formed with a diffraction grating having a certain period P at which a plurality of projection parts 103 are arrayed, formed of the same material as a substrate 102 on at least one main surface of the substrate 102; and utilizes structural birefringence of the diffraction grating. The period P of the diffraction grating satisfies P<λ/n for a wavelength λ of incident light and a refractive index n of the substrate material. The projection parts 103 are each sectioned in a tapered shape 106 from a bottom part to a top part. Here, ZnS is used as the substrate material. |
