Modification of structural and optical properties of silica glass induced by ion microbeam

Structural and optical properties of silica glass induced by ion microbeam irradiation were studied using micro- photoluminescence (μ-PL) spectroscopy and atomic force microscopy (AFM). Ion microbeam irradiation was performed using microbeam lines of 3-MV single-ended or tandem accelerators with various ion species including H⁺, He⁺, B³⁺, C⁴⁺, N⁴⁺, O⁴⁺, and Si⁵⁺ at energies of 1.7 to 18 MeV. The beam was focused to about 1 μm and was scanned over the surface of high-purity silica glass with fluences of 10¹³ to 10¹⁸ ions/cm². The μ-PL spectrum in microbeam-irradiated silica shows two peaks at 540 and 650 nm. The mapping of the two PL bands reveals the distribution of defects induced along the track of ions. The compaction was observed in the form of groove at the surface of silica glass by AFM. The depth of the surface groove increases with increasing ion fluence and saturates at about several hundreds to 900 nm, depending on irradiated ion species. The mechanisms of structural and optical modifications of silica glass are can be understood in terms of energy loss due to electronic stopping and nuclear stopping powers. Refractive index changes with an order of 10^{- 4} to 10^{- 2} were estimated by a Lorentz-Lorenz relationship from the compaction. Technological implications of these results are also to be discussed.