INFORMATION STORAGE MEDIUM

摘要

An information storage medium (1) has a base portion (2) and a code storage portion (3). The code storage portion (3) is disposed on the base portion (2) and contains an infrared absorber which absorbs substantially only infrared rays within a narrow wavelength band. If a real information storage medium (1) is produced like that, subject mediums (1, 11) are judged real or not by a method includes the steps of emitting rays to the subject medium (1, 11) , receiving rays reflected from the subject medium (1, 11), detecting a first reflectance at the peak absorption wavelength (.lambda.0) and a second reflectance at a comparison wavelength (.lambda.1) near the peak wavelength (.lambda.0), and judging if the subject medium (1, 11) is real or not. The rays at the comparison wavelength (.lambda.1) are not very much absorbed by the absorber.