| 摘要 |
PROBLEM TO BE SOLVED: To provide a focus adjustment system using a diffraction optical element, by deciding the diffraction phase profiles of a first diffraction optical element and a second diffraction optical element with a specified equation related to a position on a surface. SOLUTION: When an f value is 1, and a whole object/image view is either one of 0.5 or 1μm, an optical system is provided with a spot size of 1μm or below and Strehl ratio exceeding 0.9. A divergent light beam 14 is diffracted by the first diffraction optical element 16, and diffracted light 18 from the first diffraction optical element 16 is diffracted by the second diffraction optical element 20, and a diffracted beam 22 obtained as the result is faced to a spot 24 on an image surface 26. Since the first, second diffraction optical elements 16, 20 are circular symmetry, the diffraction phase profileΦis shown by the equationΦ(ρ)=c1ρ<2> +c2ρ<4> +c3ρ<6> +c4ρ<8> -c5ρ<10> +c6ρ<12> +c7ρ<14> +c8ρ<18> +c10ρ<20> on the positionρin the radial direction. Where, cx is a polynominal coefficient.
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