| 摘要 |
PURPOSE: To correct the evanescent wave intrusion length varying according to the wavelength changing the incident angle to the total reflection surface of a prism in accordance with the wavelength by the use of a dispersing element. CONSTITUTION: A diffraction light originating from an incident white light at a certain angle on a diffraction lattice 4 is collimated by a lens 1 having a focal distance f, and upon image inversion by two lenses 3, is converged by a lens 2 having a focal distance f. The optical axis of this lens system is laid on the line tying the center of the lattice 4 with a prism 5 which is formed into a semi-columnar shape and whose angle change due to refraction is ignorable. Because therein the desired incident angle can not be obtained so long as the dispersion angle of the lattice 4 remains as it is, the total reflection surface of the prism 5 is inclined from the optical axis so that an offset angle is generated, and thereby, the desired incident angle is established. This permits obtaining an evanescent wave intrusion length which is constant in the visible ray region. That is, it is possible to segregate beams of light having different, wavelengths using dispersing element of the lattice 4 and change the incident angle according to the wavelength by converging onto the total reflection surface by the lenses, and the evanescent wave intrusion length can be made constant. |
