Enhancement of UV laser‐induced damage resistance of the fluoride‐containing phosphate glasses by regulating the intrinsic defects

Abstract

Low fluorine content containing fluorophosphate glasses have promising potential as ultraviolet (UV) optics to be used in high-energy laser systems. Systematic studies on the iron-doped and iron-free fluoride-containing phosphate glasses that were prepared at high and low melting temperatures explore the underlying interrelationship among the glass preparation conditions, intrinsic defects in produced glasses, and the anti-laser-damage properties. For the iron-doped fundamental frequency (1ω) absorptive glass, melting at high-temperature (1200 • C) can reduce the extrinsic "impurity" concentration of Fe 3+ ions, resulting in tiny increase of optical bandgap (by 1.6%) but significant reduce of the absorption coefficient by 34% at 355 nm. However, only tiny increase of the laser-induced damage threshold (LIDT) was achieved. For the iron-free third harmonic frequency (3ω) transparent glass, low-temperature (1000 • C) melting process significantly reduced the absorptive intrinsic defects content of PO 3 -EC, PO 4 -EC, and phosphorous oxygen-bonded hole center defects, which made the UV absorption edge blue-shifted by 50 nm and the optical bandgap increased by ∼18%. The UV (355 nm) LIDT was significantly enhanced by ∼27%. Much lower absorption coefficient and larger bandgap of the iron-free glass relative to the iron-doped one endow it with larger a LIDT. In short, optimizing the glass melting temperature is a feasible method to enhance the UV laser-induced damage resistance of the fluoride-containing phosphate glasses through controlling the content of the extrinsic or intrinsic defects in produced glasses. The general routine is to achieve both the lower UV absorptive defect concentration (i.e., lower UV absorption at 355 nm) and the lower non-bridged oxygen ratio (i.e., denser glass network), as well as a larger optical bandgap (i.e., reduced probability of avalanche ionization breakdown), which together contribute to the enhancement of the anti-laserdamage performance of the investigated fluoride-containing phosphate glasses.