US Patent 7466419 Spectral instrument

In this spectral instrument, a plurality of interference filters 31, 32 . . . with transmitting wavebands different from each other are arranged in order so that light reflected by a specific interference filter 31 is made incident on the interference filter 32 on the next stage, and at positions on which light transmitted through each interference filter is made incident, photodetecting devices 41, 42 . . . are provided, wherein a silver thin film 31a with a thickness of 20 to 200 nm is provided on the light incidence surface side of the interference filter 31 on the first stage.