Abstract: Whether or not an object is present, the surface state of the object, the material constituting the object and the presence of scattering bodies are discriminated through a simple arrangement which includes a light-emitting element for projecting light upon an object to be sensed, and a polarization beam splitter upon which light reflected from the object (or light transmitted through or scattered from the object) impinges. Reflected light from the polarization beam splitter is received by a first light-receiving element, and transmitted light from the polarization beam splitter is received by a second light-receiving element. The aforesaid discrimination is performed on the basis of the value of S/P, S-P, S-kP or (S-P)/(S+P), where S and P represent light-reception signals from the first and second light-receiving elements, and k is a constant.

Abstract: A dichroic mirror of the present invention having a first portion including an H material layer having a high refractive index, and an M material layer having an intermediate refractive index, the H material layer and the M material layer being laminated repeatedly; and a second portion including an H material layer having a high refractive index, and an L material layer having a low refractive index, the H material layer and the L material layer being laminated repeatedly. An optical apparatus and detecting method of the present invention use the above dichroic mirror.

Abstract: A dichroic mirror of the present invention having a first portion including an H material layer having a high refractive index, and an M material layer having an intermediate refractive index, the H material layer and the M material layer being laminated repeatedly; and a second portion including an H material layer having a high refractive index, and an L material layer having a low refractive index, the H material layer and the L material layer being laminated repeatedly. An optical apparatus and detecting method of the present invention use the above dichroic mirror.