Analysis of defects patterned by femtosecond pulses inside KBr and SiO2 glass

• Published in: Applied physics. A, Materials science & processing Vol. 122; no. 3
• Main Authors: Wang, X. W., Buividas, R., Funabiki, F., Stoddart, P. R., Hosono, H., Juodkazis, S.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2016
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Emerging trends in photo-excitations and promising new laser ablation technologies; Invited Paper; Machines; Manufacturing; Nanotechnology; Optical and Electronic Materials; Physics; Physics and Astronomy; Processes; Surfaces and Interfaces; Thin Films; Critical Plasma Density; Indigo Blue; Electron Spin Resonance; Colour Centre; Front Tilt
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-016-9647-0

Colour centres in KBr and defects in silica glass were formed by focused femtosecond laser pulses. It is shown that under simple laser exposure, KBr develops a similar colouration as that achieved with electron and ion bombardment or high-energy X-ray irradiation. The three-dimensional (3D) character of direct laser writing in the volume of KBr allows a new level of control in the spatial arrangement of colour centres and defects. Five different colour centres were identified in KBr through the absorption spectrum; they have different charge and vacancy distribution configurations. The densities of the V- and F-centres were estimated to be 3.9 × 10 19 and 3.4 × 10 19  cm −3 using Smakula’s formula. In silica, a high density of paramagnetic E ′ centres ~1.9 × 10 20  cm −3 was determined by quantitative electron spin resonance spectroscopy. Birefringence due to colour centres and laser-induced defects was measured using Stokes polarimetry. In the case of colour centres in KBr, retardation in excess of 0.05 π was determined throughout the visible spectrum from 400 to 800 nm. The use of polariscopy for analysis of high-pressure and high-temperature phase formation induced by 3D laser structuring is discussed.