Near-field light generator and thermally-assisted magnetic recording head

A near-field light generator comprising a waveguide, a plasmon generator, and a metal layer, wherein:

• the waveguide includes a core through which light propagates, and a cladding that surrounds the core;
• the core has an evanescent light generating surface that generates evanescent light based on the light propagating through the core;
• the core and the metal layer are located on the same side relative to the plasmon generator in a first direction perpendicular to the evanescent light generating surface;
• the plasmon generator includes a base part and a protruding part, the protruding part protruding from the base part toward the evanescent light generating surface;
• the base part has a first base surface and a second base surface that face toward the evanescent light generating surface and are located on opposite sides of the protruding part in a second direction parallel to the evanescent light generating surface, the first and second base surfaces being parallel to the evanescent light generating surface;
• the protruding part has:
• a front end face located at an end in a third direction orthogonal to the first and second directions;
• a flat surface that is shaped like a band and elongated in the third direction, the flat surface facing toward the evanescent light generating surface and being parallel to the evanescent light generating surface;
• and a first side surface and a second side surface that are at a distance from each other;
• the flat surface is located closer to the evanescent light generating surface than are the first and second base surfaces;
• the first side surface connects the flat surface to the first base surface;
• the second side surface connects the flat surface to the second base surface;
• in at least a portion of the protruding part, a distance between the first and second side surfaces in the second direction increases with increasing distance from the evanescent light generating surface;
• the front end face includes a near-field light generating part that generates near-field light;
• the flat surface includes a first portion contiguous with the front end face, and a second portion that is located farther from the front end face than is the first portion;
• the metal layer has an end face that faces the first portion of the flat surface;
• the evanescent light generating surface faces the second portion of the flat surface;
• a difference in level between the flat surface and each of the first and second base surfaces in the first direction falls within a range of 20 to 50 nm;
• the flat surface has a width in the second direction within a range of 5 to 35 nm;
• and
• the first portion of the flat surface and the end face of the metal layer are at a distance within a range of 10 to 40 nm from each other,
• the near-field light generator being configured so that a surface plasmon is excited on at least the second portion of the flat surface of the plasmon generator through coupling with the evanescent light generated from the evanescent light generating surface, the surface plasmon propagates along the flat surface to the near-field light generating part, and the near-field light generating part generates the near-field light based on the surface plasmon.