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16LP-PS-14
Compressed laser-induced ^-plasma (CLI^P) for fused silica structuring: ps vs ns
V. V. Koval1, V.S. Rymkevich1, A. A. Samohvalov1, V. Veiko1 1ITMO University, Saint Petersburg, Russia
Glass microstructuring by CLIpP is a very promising method for different applications upon making any micro-analytic systems as well as microoptical and diffractive elements [1,2]. In our method plasma extension is limited by the close contact between a glass plate and a highly absorbing target, so it's compressed (Fig.la). Such plasma induced by ~50 ns pulses of Yb:fiber laser have ~1.5 ps lifetime and becomes q-CW with repetition rate in the range of ~100 kHz. Fused silica microstructuring under these conditions require multipulse processing mode, because an etching rate is rather small and is about 20 - 50 nm/pulse with fluences ~6 J/cm2 (1.3-108 W/cm2). These regimes can be useful for precision DOE fabrication, but high depth relief on fused silica is not available. Also, a width of craters in multipulse regimes are higher than a laser beam spot size. In order to minimize plasma plume volume and to achieve higher etching rates it's suggested to use laser radiation of picosecond pulse duration range. For fluences in the range below ~6 J/cm2 (2-1011 W/cm2 for 30 ps) the etching rate is up to 700 nm/pulse and a crater width is smaller than a laser beam spot, that can caused by plasma-focusing effects. For higher fluences higher etching rates are possible, but in this case strong nonlinear effects define relief formation processes. However, high peak fluences in CLImP are limited by laser-induced damage threshold of the free fused silica surface, that in the case of 30 ps pulses is measured to be -12 J/cm2.
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Fig. 1. Schematic of CLI^P processes (a), dependence of relief depth on laser fluence for 30 ps pulses (b), profile of
single pulse crater (c).
The reported study was financially supported by the Ministry of Education and Science of the Russian Federation, research agreement No. 14.587.21.0037 (RFMEFI58717X0037).
References
[1] Veiko, V. P., Volkov, S. A., Zakoldaev, R. A., Sergeev, M. M., Samokhvalov, A. A., Kostyuk, G. K., & Milyaev, K. A. (2017) Laser-induced microplasma as a tool for microstructuring transparent media. Quantum Electronics, 47(9), 842.
[2] Kostyuk, G. K., Zakoldaev, R. A., Koval, V. V., Sergeev, M. M., & Rymkevich, V. S. (2017). Laser microplasma as a tool to fabricate phase grating applied for laser beam splitting. Optics and Lasers in Engineering, 92, 63-69.
