DATA READING WITH THE AID OF ONE-PHOTON AND 2-PHOTON LUMINESCENCE IN 3-DIMENSIONAL OPTICAL MEMORY DEVICES BASED ON PHOTOCHROMIC MATERIALS

The problem of nondestructive reading of the data stored in the interi or of a photochromic sample was analysed, A comparison was made of the feasibility of reading based on one-photon and two-photon luminescenc e, A model was proposed for the processes of reading the data stored i n photochromic molecules with the aid of one-photon and two-photon lum inescence. In addition to photochromic transitions, account was taken of the transfer of populations between optically coupled transitions i n molecules under the action of the exciting radiation, This model pro vided a satisfactory description of the kinetics of decay of the colou red form of bulk samples of spiropyran and made it possible to determi ne experimentally the quantum yield of the reverse photoreaction as we ll as the two-photon absorption cross section of the coloured form. Me asurements were made of the characteristic erasure times of the data s tored in a photochromic medium under one-photon and two-photon lumines cence reading conditions, It was found that the use of two-photon lumi nescence made it possible to enhance considerably the contrast and loc alisation of the optical data reading scheme in three-dimensional opti cal memory devices, The experimental results were used to estimate the two-photon absorption cross section of the coloured form of a sample of indoline spiropyran in a polymethyl methacrylate matrix.