| 摘要 |
PROBLEM TO BE SOLVED: To provide a diffraction optical device having a grating part with substantially a sawtooth or step-like cross section and in particular, to provide a device having a period in the order of the wavelength (for example, in the size of <=1.6 times as the wavelength) which can increase the diffraction angle and having high efficiency for the incident light from the upper part of the grating. SOLUTION: The device has a substrate 1 and a grating part 2 formed on the substrate 1. The peripheral part 2a of the grating 2 has the period of <=Λ1 which substantially satisfiesΛ1=λ[0.7529+12.49617 exp(-n/0.56743)] with respect to the refractive index n and incident wavelength, of the grating part 2, and the cross section of the grating part having the above period shows a sawtooth or step-like form. In the device, the -1-order diffracted light of the incident light from the upper position of the grating part is used and condensed.
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