| 摘要 |
A diffraction grating comprises the plurality of grating rings provided at positions such that their radii r are selected so that a function phi (r) of r satisfies the following differential equation and initial conditions, <IMAGE> +TR <IMAGE> phi (0) = specific real number, and <IMAGE> where lambda is the wavelength of a scanning light beam, f is the focal length of the diffraction grating, r is the radius from the center of diffraction grating, M is the distance from the diffraction grating to a scanning surface expressed as a multiple of the focal length f, and moreover the relation phi (r)=n+ phi (0) n=0, 1, 2, . . . (n is a non-negative integer) is satisfied.
|
