| 摘要 |
PROBLEM TO BE SOLVED: To provide an illumination optical system which is constituted compact in size, more particularly, the illumination optical system which can be lowered in the height of a stage, and to provide an optical device using this illumination optical system. SOLUTION: A diffraction optical element is arranged between a light source and an object. This diffraction optical element is provided with patterns for deflecting the luminous flux from the light source to the object side. If the direction normal to the surface of the stage for holding the object is defined as Z-axis, and the angle formed by a normal to the surface of the diffraction optical element and the Z-axis is defined asα, the diffraction optical element is so arranged as to satisfy the equation 0 deg.<α<45 deg.. The illumination optical system, having the diffraction optical element described above, is used for the optical device.
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