Fluorescent detecting apparatus and method

摘要

A fluorescent light emitted from a marking containing at least one fluorescent substance is detected by illuminating the marking with an exciting light having an intensity that varies at a predetermined cycle, converting a change in intensity of light reflected from a position where the exciting light is irradiated into a varying electric signal and selectively extracting from the converted electric signal, only an electric signal component having a frequency matching with but a phase displaced from, that of a signal component corresponding to light reflected from the marking. A fluorescent detecting apparatus for this purpose includes a light source for irradiating at an irradiating station a marking formed on a medium with rays of light having an intensity that varies cyclically, the marking having at least one fluorescent substance. The apparatus further includes a photo-electric detector for detecting incident rays of light reflected from the irradiating station and converting the rays of light into an electric signal, and a phase detector for extracting from the electric signal respective signal components corresponding to the rays of light reflected from the marking and the medium, respectively.