Curable resin composition, cured product, diffractive optical element, multilayer diffractive optical element, and method for producing curable resin composition

A curable resin composition comprising:

• a bifunctional or more (meth)acrylate compound;
• indium tin oxide particles;
• and
• an acidic polymer,
• wherein the acidic polymer has a moiety including a carboxyl group at a polymer skeleton of a (meth)acrylate compound and at any one of terminals of the polymer skeleton of a (meth)acrylate compound,
• the acid value of the acidic polymer is 2.0 mgKOH/g or more and less than 100 mgKOH/g, and
• the acidic polymer is represented by Formula (1),
• (R1—S—L2)n—L1—(L3—A—R2)m . . . (1)
• wherein in Formula (1), R1 represents a substituent including at least one carboxyl group, A represents a polymer skeleton of a (meth)acrylate compound, R2 represents a hydrogen atom or a substituent not including a carboxyl group, L1 represents a single bond or a (m+n)-valent linking group, L2 and L3 each independently represents a single bond or a divalent linking group, m represents an integer of 1 to 8, and n represents an integer of 1 to 9, in which m+n satisfies 2 to 6, each of n, R1, and L2 may be the same as or different from each other, and each of m, R2, A, and L3 may be the same as or different from each other.