Diffuser and method for manufacturing the same

A method for manufacturing a diffuser provided with a recess-protrusion structure,

• wherein when a z-axis is defined as a normal to a flat surface of a substrate, and an x-axis is defined on the flat surface, the method includes the steps of
• dividing the x-axis into plural intervals such that the relationship
• 2<Sx′-max/Sx′-min
• holds, and Snx′ varies on a random basis between Sx′-min and Sx′-max, where nx′ represents a positive integer for identifying an interval along the x-axis, Snx′ represents length in the x-axis direction of an interval nx′, Sx′-max represents the maximum value of Snx′, and Sx′-min represents the minimum value of Snx′;
• forming a provisional recess-protrusion structure on the substrate by etching such that in an xz cross section, a recess portion and a protrusion portion are formed on each of adjacent intervals along the x-axis, respectively;
• and
• forming a synthetic resin coating on the provisional recess-protrusion structure by spin coating such that the relationship
• Ax-max/Ax-min<1.3
• holds, where an interval nx represents an interval along the x-axis that corresponds to a recess portion or a protrusion portion of the recess-protrusion structure coated with the synthetic resin coating in the xz cross section, Snx represents length in the x-axis direction of the interval nx, dznx represents a difference between the maximum value and the minimum value of z coordinate of the recess-protrusion structure in the interval nx in the xz cross section, Anx represents a ratio between dznx and Snx, Anx-max represents the maximum value of Anx, and Anx-min represents the minimum value of Anx.