[INVITED] On the mechanisms of single-pulse laser-induced backside wet etching. (February 2017)

• Record Type: Journal Article
• Authors: Tsvetkov, M.Yu.; Yusupov, V.I.; Minaev, N.V.; Akovantseva, A.A.; Timashev, P.S.; Golant, K.M.; Chichkov, B.N.; Bagratashvili, V.N.
• Is Part Of: Optics & laser technology. Volume 88(2017)
• Page Start: 17
• Page End: 23
• Publication Date: 2017-02
• Subjects: Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2016.05.020
• Languages: English
• ISSNs: 0030-3992

Abstract

Abstract: Laser-induced backside wet etching (LIBWE) of a silicate glass surface at interface with a strongly absorbing aqueous dye solution is studied. The process of crater formation and the generated optoacoustic signals under the action of single 5 ns laser pulses at the wavelength of 527 nm are investigated. The single-pulse mode is used to avoid effects of incubation and saturation of the etched depth. Significant differences in the mechanisms of crater formation in the "soft" mode of laser action (at laser fluencies smaller than 150 – 170 J/cm 2 ) and in the "hard" mode (at higher laser fluencies) are observed. In the "soft" single-pulse mode, LIBWE produces accurate craters with the depth of several hundred nanometers, good shape reproducibility and smooth walls. Estimates of temperature and pressure of the dye solution heated by a single laser pulse indicate that these parameters can significantly exceed the corresponding critical values for water. We consider that chemical etching of glass surface (or molten glass) by supercritical water, produced by laser heating of the aqueous dye solution, is the dominant mechanism responsible for the formation of crater in the "soft" mode. In the "hard" mode, the produced craters have ragged shape and poor pulse-to-pulse reproducibility. Outside the laser exposed area, cracks and splits are formed, which provide evidence for the shock induced glass fracture. By measuring the amplitude and spectrum of the generated optoacoustic signals it is possible to conclude that in the "hard" mode of laser action, intense hydrodynamic processes induced by the formation and cavitation collapse of vapor-gas bubbles at solid–liquid interface are leading to the mechanical fracture of glass. The LIBWE material processing in the "soft" mode, based on chemical etching in supercritical fluids (in particular, supercritical water) is very promising for structuring of optical materials.