Evidence of a green luminescence band related to surface flaws in high purity silica glass

J Fournier,P Grua,D Talaga,V Jubera,J Néauport,E Fargin,S Jouannigot

doi:10.1364/oe.18.021557

Abstract

Using luminescence confocal microscopy under 325 nm laser excitation, we explore the populations of defects existing in or at the vicinity of macroscopic surface flaws in fused silica. We report our luminescence results on two types of surface flaws: laser damage and indentation on fused silica polished surfaces. Luminescence cartographies are made to show the spatial distribution of each kind of defect. Three bands, centered at 1.89 eV, 2.75 eV and 2.25 eV are evidenced on laser damage and indentations. The band centered at 2.25 eV was not previously reported in photo luminescence experiments on indentations and pristine silica, for excitation wavelengths of 325 nm or larger. The luminescent objects, expected to be trapped in sub-surface micro-cracks, are possibly involved in the first step of the laser damage mechanism when fused silica is enlightened at 351 nm laser in nanosecond regime.

Highlights

Fused silica damage at the wavelength of 351 nm (3.53 eV) in nanosecond regime is a major issue for the optimal operation of high power laser facilities, such as LMJ [1] or NIF [2] devices, devoted to inertial confinement fusion studies
Using luminescence confocal microscopy under 325 nm laser excitation, we explore the populations of defects existing in or at the vicinity of macroscopic surface flaws in fused silica
We report our luminescence results on two types of surface flaws: laser damage and indentation on fused silica polished surfaces

Summary

Introduction

Fused silica damage at the wavelength of 351 nm (3.53 eV) in nanosecond regime is a major issue for the optimal operation of high power laser facilities, such as LMJ [1] or NIF [2] devices, devoted to inertial confinement fusion studies. From a structural point of view, two luminescent defects are well known in silica [5]: the ODC (Oxygen Deficient Center) and the NBOHC (Non Bridging Oxygen Hole Center). Laurence et al [10] performed high sensitivity time resolved photoluminescence confocal microscopy on laser damage sites and indentations, luminescence spectra were not shown in this paper. They reported a fast photoluminescence signal linked to strongly absorbent areas in laser damage. We conclude that if ODC and NBOHC defects are regularly seen, the 560 nm band is randomly reported and unexplained

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