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Abstract

An invisible information recording medium includes an underlying layer, an invisible information recording layer provided above the underlying layer, being invisible under visible light, and fluorescing upon being applied with light having a particular wavelength excepting that of the visible light, thus becoming visible, and an optical modulation layer provided between the underlying layer and the recording layer. When the modulation layer includes a photochromic layer, an information reading apparatus for reading information from the medium includes a preliminary coloring unit for coloring the photochromic layer of the modulation layer in advance, and an information reading optical system for applying the light having the particular wavelength excepting that of the visible light to the recording layer to cause the recording layer to fluoresce after the photochromic layer is turned to the colored state by the coloring unit, thereby making the recording medium visible, and reading information from the recording layer which has become visible. When the optical modulation layer includes an optical polarizing film, an information reading apparatus for reading information from the medium includes an information reading optical system for reading information from the recording layer which has become visible, and an optical polarizing unit, interposed between the recording layer and the optical system and having an optical polarizing angle perpendicular to that of the polarizing film, for guiding light from the recording layer which has become visible to the optical system.

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First Claim