Fine structure, optical member, antireflection film, water-repellent film, substrate for mass spectrometry, phase plate, process for producing fine structure, and process for producing antireflection film

An optical member, comprising:

• a substrate;
• and
• an antireflection film disposed on a surface of the substrate,
• wherein the antireflection film comprises salient portions on a surface thereof,
• wherein the salient portions have such a shape that an area of a cross section when the salient portions are cut by a plane perpendicular to a direction from a bottom of the salient portions to a tip thereof reduces along the direction,
• wherein the salient portions comprise a mesostructure including mesopores,
• wherein a metal element is present at the tip of the salient portions,
• wherein a ratio H/D is 2.0 or more, where D is a length of a bottom line of the salient portions and H is a height of the salient portions,
• wherein an inorganic material having a refractive index different from that of a material of a wall portion forming the mesopores is present inside the mesopores,
• wherein a difference in refractive index between the antireflection film including the inorganic material and the substrate is smaller than a difference in refractive index between the antireflection film not including the inorganic material and the substrate, and
• wherein 0.1<σ/p<0.5, where p is an average interval between tips of the salient portions adjacent to each other and σ is a standard deviation of a distribution of intervals between the tips.