| 摘要 |
PURPOSE:To improve resolution by a simple method by arranging plural diffraction grating surfaces radially and in parallel to an axis, and bending an objective beam of spectral distribution and performing relative spectral distribution several times, and forming a spiral track. CONSTITUTION:Four diffraction grating plates 3a-3d having the same diffraction grating surfaces formed of a hologram are arranged radially at intervals of 90 deg., and the spaces between diffraction grating plates are charged with transparent media 5a-5d such as lens bond. When the diffraction grating of this constitution performs spectral distribution, an incident beam C as the objective beam of spectral distribution is projected slightly slantingly to a plene perpendicular to the axis Z of the arrangement of the diffraction grating plates 3a-3d so that a beam reflected by a mirror surface 4d is incident to the diffraction grating plate 3a at an angle of incidence of about 45 deg. and then the incidence beam C is refracted repeatedly to make three turns in the diffracting element, and diffracted by the diffraction grating plate 3d for the 12th time to obtain a projection beam Ca, which is reflected by a mirror surface 4a and guided out. |
