| 摘要 |
PURPOSE:To improve the resolution of a spectrum by providing a backward optical element which projects two pieces of opposite incident luminous flux in their incidence directions regardless of the mutual incidence directions in a parallel free movement state in an optical path where the two pieces of luminous flux split by a beam splitter travel in the mutually opposite directions. CONSTITUTION:The incident parallel luminous flux from am plane mirror 15 is split into two pieces of luminous flux, i.e. transmitted luminous flux and reflected luminous flux on the beam splitter 16 and the transmitted luminous flux is reflected and made incident on the optical path between plane mirrors 17 and 18 and the reflected luminous flux is reflected by the plane mirror 18 and made incident on the optical path. Both pieces of luminous flux are incident on a composite type Littrow reflecting mirror 21 in the mutually opposite directions, but the transmitted luminous flux is reflected by one Littrow reflecting mirror 19 so as to travels backward in the incidence direction and the reflected luminous flux is reflected by the other Littrow reflecting mirror 20 to travel backward in its incidence direction and they are reflected by the plane mirrors 17 and 18 to reach the beam splitter 16 and then interfere with each other, so that interference light is observed. The opposite optical path difference is increased or decreased by the scanning of the composite type Littrow type reflecting mirror 21 to obtain the opposite optical path difference which is twice as large as that of a conventional Michelson interferometer.
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