Photothermal conversion element, method of manufacturing the same, photothermal power generator, and microscopic object collection system

A method of manufacturing a photothermal conversion element comprising:

• providing a solid material;
• and
• forming a processed region processed by irradiation of the solid material with a focused laser beam, wherein:
• the forming includes grain refining the solid material to blacken the processed region by a collection of a plurality of fine particles composed of the solid material,
• the plurality of fine particles produce localized surface plasmon resonance on a surface of each of the plurality of fine particles by irradiation with light,
• the forming includes scanning with the focused laser beam to provide, by cutting, a plurality of microgrooves in the processed region, and
• the scanning includes scanning the focused laser beam with a scanning interval and a spot height such that resultant average reflectance in a visible range of the processed region is 0.42% or less.