2016, №2

сс. 14-27

On the Role of Supercritical Water in Laser-Induced Backside Glass Wet Etching

2016, №2

сс. 14-27

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M.Yu. Tsvetkov, V.I. Yusupov, P.S. Timashev, K.M. Golant, N.V. Minaev, S.I. Tsypina, V.N. Bagratashvili

Key words: laser-induced liquid etching, supercritical water, cavitation, microstructuring

The features and mechanisms of microcrater formation in optical silicate glass by
laser-induced backside wet etching (LIBWE) are determined in a wide range of energy
density (F) from 4 to 103 J/cm2 for laser pulses of 5 ns length and 1 kHz repetition rate.
The existence of two different mechanisms of laser-induced microcrater formation is
revealed: (i) chemical etching in supercritical water (SCW), and (ii) cavitation. At
Φ > 102 J/cm2 irregular craters of 1—20 microns in depth with rough walls and distinct
cracks around microcrater are formed testifying that in such mode («hard») laser
induced cavitation plays a dominant role in glass removal. At Φ < J/cm2 neat glass craters
with smooth walls are formed, their size and shape are well reproducible, cracks are not
formed, and processing area is limited to the laser spot area. In this mode («soft mode
with active cavitation»), a microcirculation of water is stimulated by cavitation without
causing undesirable shock breakage. The latter is achieved thanks to the fast removal of
glass etching products by microcirculation, and the inflow of «fresh» etchant (SCW) to
the glass surface in the vicinity of the formed microcraters. Such mode is optimal for
highly controlled laser microstructuring of glass and other optically transparent materials.

doi:10.1134/S1990793117070181