Three-dimensional optical storage recording by microexplosion in a doped PMMA polymer

Three-dimensional optical data storage realized by microexplosion based on a multi-photon absorption process is a promising method to fabricate optical read-only memory with large recording capacity. The writing of multi-layered data bits inside a PMMA block doped with rare-earth ions (Sm³⁺ and Ce³⁺) under multi-photon absorption excited by a 800nm femtosecond (fs) pulsed laser was reported. The fs pulsed laser beam was focused into the sample with a microscope objective (N.A.= 0.65 40X), and bits were recorded as structurally altered regions which have high contrast in refraction index and fluorescence intensity. The recorded bits could be retrieved parallel by transmission using a conventional optical microscope or be read out serially by fluorescence signal of the structurally altered region excited by a 514.5nm laser using a reflect-type confocal microscope. Experimental results of three-dimensional recording and reading with 4-um in-plane bit spacing and 8-um inter-plane spacing in eight layers were presented. The structure changed in the material before and after the laser irradiation was discussed.