An azobenzene-containing urethane-urea copolymer as a photochromic material has two optical properties for data storage. One is photoisomerization related to the polarization of incident beam. The other is photoablation related to the intensity of incident beam. It seemed that we could separate them with the power or wavelength of the recording beam. Therefore, we studied the characteristics of the phenomena and found that the selective use of the effects is applicable to some types of memory.
Aoshima, Y., Egami, C., Kawata, Y., Sugihara, O., Tsuchimori, M., Watanabe, O., … Okamoto, N. (1999). Two-way optical memory for azobenzene-containing urethane-urea copolymer films. Optics Communications, 165(4), 177–182. https://doi.org/10.1016/S0030-4018(99)00242-4