Optimisation of microlenses fabricated by deep proton irradiation and styrene diffusion

Microlenses with high relative aperture can be fabricated in PMMA by irradiation with energetic proton beams and diffusion of monomer vapour into the irradiated domains. For good reproducibility of the experiments, stable conditions regarding the temperature and pressure during diffusion have to be guaranteed and the deposited dose in the PMMA must be controlled exactly. A diffusion apparatus has been designed and constructed in order to precisely control the diffusion parameters. Microlenses were fabricated on PMMA substrates, which have been irradiated with 3 MeV proton beam through a metal mask with circular apertures. The curing of the microlenses has been done successfully with 254 nm UV, which is highly absorbed by styrene. Ranges of the diffusion temperature and the diffusion time for the proper swelling have been determined experimentally as a function of deposited fluence in a range between 5 X 10(12) and 5 X 10(13) ions/cm(2). (C) 2001 Elsevier Science B.V. All rights reserved.