Information storage medium and method for detecting forgeries

Abstract

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

What is claimed is:  
     
       1. An information storage medium comprising: 
       a base portion; and  
       a code storage portion disposed on said base portion, said code storage portion containing an infrared absorber, said infrared absorber being capable of absorbing substantially only infrared rays within a narrow wavelength band, wherein said infrared absorber has a first reflectance at said narrow wavelength band and a second reflectance at a second wavelength at a critical point of said narrow band, said infrared absorber absorbing infrared at said first wavelength most, the difference between the first reflectance  wavelength and the second reflectance  wavelength being equal to or less than 100 nm.  
     
     
       2. A method for judging if a subject information storage medium is real or a forgery wherein a real information storage medium includes a base portion and a code storage portion disposed on said base portion, said code storage portion containing a light absorber, said light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength at which the light absorber absorbs the most, the method comprising the steps of: 
       emitting rays onto said subject information storage medium;  
       receiving rays reflected from said subject medium;  
       detecting a first reflectance at said peak wavelength and a second reflectance at a comparison wavelength near said peak wavelength, rays at the comparison wavelength not being significantly absorbed by said light absorber; and  
       judging if said subject medium is real or not on the basis of said first reflectance and said second reflectance.  
     
     
       3. A method according to  claim 2 , wherein said judging step comprising obtaining a difference between said first reflectance and said second reflectance, and judging said subject medium to be real if said difference between said first reflectance and said second reflectance is greater than a certain value, and judging said subject medium to be a forgery if said difference is equal to or less than said certain value. 
     
     
       4. A method according to  claim 3 , wherein said light absorber is capable of absorbing substantially only infrared rays within a narrow wavelength band, said rays used at said emitting step containing at least infrared rays which are absorbed by said light absorber. 
     
     
       5. A method according to  claim 4 , wherein a difference between said peak wavelength and said comparison wavelength is greater than 10 nm and equal to or less than 100 nm. 
     
     
       6. A method according to  claim 2 , wherein said light absorber is capable of absorbing substantially only infrared rays within a narrow wavelength band, said rays used at said emitting step containing at least infrared rays which are absorbed by said light absorber. 
     
     
       7. A method according to  claim 6 , wherein a difference between said peak wavelength and said comparison wavelength is greater than 10 nm and equal to or less than 100 nm. 
     
     
       8. An apparatus for judging if a subject information storage medium is real or a forgery wherein a real information storage medium includes a base portion and a code storage portion disposed on said base portion, said code storage portion containing a light absorber, said light absorber being capable of absorbing substantially only specific rays within a narrow wavelength band, the narrow wavelength band including a peak wavelength at which the light absorber absorbs the most, the apparatus comprising: 
       an emitting means for emitting rays onto said subject information storage medium, said rays containing at least rays of said peak wavelength and rays of a comparison wavelength near said peak wavelength, rays at the comparison wavelength not being significantly absorbed by said light absorber;  
       receiving means for receiving rays reflected from said subject medium, and providing a first output signal in accordance with a first reflectance at said peak wavelength and a second output signal in accordance with a second reflectance at said comparison wavelength; and  
       a judging means for obtaining a difference between said first signal and said second signal, and judging if said subject medium is real or not on the basis of said difference between said first signal and said second signal.  
     
     
       9. An apparatus according to  claim 8 , wherein said judging means judges said subject medium to be real if said difference between said first signal and said second signal is greater than a certain value and judges said subject medium to be a forgery if said difference is equal to or less than said certain value. 
     
     
       10. An apparatus according to  claim 9 , wherein said emitting means emits at least infrared rays for inspecting said subject medium when said light absorber of said real information storage medium is an infrared absorber, said infrared absorber being capable of absorbing substantially only infrared within a narrow wavelength band. 
     
     
       11. An apparatus according to  claim 10 , wherein a difference between said peak wavelength and said comparison wavelength, by which said receiving means provides said first and second output signals, is greater than 10 nm and equal to or less than 100 nm. 
     
     
       12. An apparatus according to  claim 8 , wherein said emitting means emits at least infrared rays for inspecting said subject medium when said light absorber of said real information storage medium is an infrared absorber, said infrared absorber being capable of absorbing substantially only infrared within a narrow wavelength band. 
     
     
       13. An apparatus according to  claim 12 , wherein a difference between said peak wavelength and said comparison wavelength, by which said receiving means provides said first and second output signals, is greater than 10 nm and equal to or less than 100 nm.