Concave diffraction grating and a manufacturing method thereof

摘要

A tool for ruling grating grooves is reciprocated on a diffraction grating blank with the tool being restrained within a plane inclined at an arbitrary angle relative to a plane lying in contact with one point on a spherical concave of the diffraction grating blank. Translation for a variable pitch-groove spacing which changes as a function of the groove number or groove position is imparted to the diffraction grating blank in interlocking relationship with the reciprocation, thereby mechanically ruling the desired sphere of the grating blank with the grating grooves, whereby a concave diffraction grating which forms diffracted light of a specific wavelength into a completely stigmatic image at high diffraction efficiency can be manufactured.