Phase transformations initiated by optical breakdown in bulk of fused silica. (February 2021)

• Record Type: Journal Article
• Authors: Rehman, Z.U.; Ullah, S.; Qayyum, H.; Irfan, M.; Tran, K.A.; Suk, H.; Qayyum, A.; Janulewicz, K.A.
• Is Part Of: Optics & laser technology. Volume 134(2021)
• Publication Date: 2021-02
• Subjects: Fused silica -- Microexplosion -- Extreme thermodynamics -- Phase transformation -- Nano-crystallization -- Amorphous material; Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2020.106630
• Languages: English
• ISSNs: 0030-3992

Abstract

Highlights: Laser-induced optical breakdown inside fused sillica. Formation of localized nano-crystalline phase near the geometrical focus. Observation of laser-induced high temperature/pressure phase transition by laser breakdown. Presence of high pressure phase of silica; stishovite. Abstract: Optical breakdown inside a transparent dielectric triggered by a tightly focused laser beam has a character of microexplosion. As a result, extreme thermodynamic conditions are generated in the material. Both high pressure and high temperature combine in causing major structural transformations (phase transitions). This work presents mapping of such structural changes initiated by microexplosion in bulk of fused silica. The high-resolution cross-sectional imaging with high-resolution electron microscopy (HRTEM) revealed transition area between the amorphous and crystalline phases of the material affected by high pressure and temperature. It was found that the crystalline phase is created in the form of nano-crystals (crystallites) embedded in an amorphous matrix and is located mainly in the vicinity of the geometrical focus. The range of this finding was extended by the spectral analysis indicating redistribution, spatial segregation, and glass network reorganization paths leading to material densification. Closer inspection of the densified area with help of micro-photoluminescence (PL) confirmed appearance of the crystalline structure. Physical mechanisms included in such a transformation process and the main features of the created glass ceramic are also discussed.