Patent ID: 8435346

Claim:
A phase modulation element provided together with an image formation optical system to provide a light intensity distribution of a repeated pattern, having a phase distribution based on a phase modulation unit having a predetermined size, comprising: a first area having a first phase value; and a second area having a second phase value, wherein the phase distribution is defined by a change in area shares of the first area and the second area depending on each position, and wherein said repeated pattern exhibits a minimum light intensity at a certain position and the light intensity increasing from the certain position toward the periphery of the pattern, the phase modulation unit predetermined size being optically smaller than a radius of a point spread distribution range of the image formation optical system, to provide the light intensity distribution of the pattern, and wherein the phase modulation unit, when the image formation optical system has a homogeneous circular pupil and no aberration, has the following relationship between the point spread function ASF of the image formation optical system and the pupil function: ASF(x,y)∝2j 1 (2π/λ·NA·r)/(2π/λ·NA·r) where r=(x 2 +y 2 ) 1/2 , J 1 indicates a Bessel function, λ indicates a wavelength of light beams, and NA indicates an image side numeral aperture of the image formation optical system.