Formation of voids in a doped polymethylmethacrylate polymer

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Abstract
We report on the formation of submicrometer voids within a doped polymethylmethacrylate (PMMA) polymer under multiphoton absorption excited by an infrared laser beam. An ultrashort pulsed laser beam of pulse width 80 fs at a repetition rate of 82 MHz and a wavelength of 800 nm is focused into a PMMA-based photorefractive polymer consisting of 2,5-dimethyl-4(p-nitrophenylazo)anisole, 2,4,7-trinitro-9-fluorenone, and N-ethylcarbazole. The large change in refractive index associated with a void allows confocal reflection microscopy to be used as a detection method. Voids can be arranged in a multilayered structure for read-only high-density optical data storage.