Abstract: An optical unit includes a reflective optical element and an antireflection structure having an average height and an average pitch larger than a maximum wavelength of light contained in an effective light flux. The antireflection structure is disposed outside an optical path of the effective light flux, and the antireflection structure has a plurality of convex portions extending in a predetermined direction. An angle formed between the predetermined direction and the optical path of the effective light flux is from 45 degrees to 60 degrees.

Abstract: An optical element formed of a plurality of materials includes a middle layer between a base material and a reflecting member so as to suppress stripping, cracking and the like of the optical surface due to the difference in coefficients of thermal expansion among the component materials, in the case where a temperature difference in the service environment or a temperature difference between a manufacturing environment and the service environment is large.

Abstract: An optical element formed of a plurality of materials includes a middle layer between a base material and a reflecting member so as to suppress stripping, cracking and the like of the optical surface due to the difference in coefficients of thermal expansion among the component materials, in the case where a temperature difference in the service environment or a temperature difference between a manufacturing environment and the service environment is large.

Abstract: A diffusing plate includes a microlens array in which a plurality of microlenses are arranged, wherein the microlenses have such a shape that a curvature of a sectional shape including a center line of the microlenses varies depending on a direction of the center line, and wherein microlenses that are different in the direction of a center line where the curvature of the outline is largest are arranged.

Abstract: An optical element formed of a plurality of materials includes a middle layer between a base material and a reflecting member so as to suppress stripping, cracking and the like of the optical surface due to the difference in coefficients of thermal expansion among the component materials, in the case where a temperature difference in the service environment or a temperature difference between a manufacturing environment and the service environment is large.

Abstract: A diffusing plate includes a microlens array in which a plurality of microlenses are arranged, wherein the microlenses have such a shape that a curvature of a sectional shape including a center line of the microlenses varies depending on a direction of the center line, and wherein microlenses that are different in the direction of a center line where the curvature of the outline is largest are arranged.