| 摘要 |
PURPOSE:To enable to read out the high density recording of the titled medium by composing the medium of plural photochromic compds. in which said compds. are overlapped at one of the light absorption wavelength region and are different with each other at another one of the light absorption wavelength region. CONSTITUTION:The photochromic compd. is composed of a spiroran, etc., and the plural photochromic compds. comprises for example, the compds. I and II, and the compd. I comprises a discoloring type compd. IB and a coloring type compd. IC, and the compd. II comprises a discoloring type compd. IIB and a coloring type compd. IIC. And, the light absorption wavelength lambda1 of the discoloring type IB of the compd. I is different from that lambda2 of the discoloring type IIB of the compd. II, and the light absorption wavelength lambda3 of the coloring type IC of the compd. I and that of the coloring type IIC of the compd. II are overlapped with each other. The titled medium is formed by selecting said compds. I and II in which said compds. are overlapped at one of the light absorption wavelength region, and are different with each other at another one of the light absorption wavelength region. And, in case of recording to the titled medium, the wavelengths lambda1 and lambda2 are used, and in case of reading out from the titled medium, a weak light of wavelength lambda3 is used. In case of erasing the recording, the strong light of wavelength lambda3 is used. Accordingly, the high density recording can be read out from the titled medium by a single light source. |
