Matter in super-strong field and formation of Warm Dense Matter by confined microexplosion
We use ultrashort femtosecond laser beam with very high peak intensity to create micro-expostions in solid materials.
The quest for recreating the high pressure and high temperature in laboratory experiments, which regulate the processes inside the stars and planets is a driving force for our studies of Warm Dense Matter (WDM), a non-equilibrium state of matter between solid and plasma: it has high, solid-state density, and low plasma temperature of 1 eV – 10 eV. The extreme conditions produced in the ultrafast laser driven micro-explosions can serve as a novel microscopic laboratory for high pressure and temperature studies and materials processing, well beyond the pressure levels achieved in diamond anvil cell.
Our X-ray microanalysis of the compressed shell in sapphire demonstrated that a new stable high-pressure phase, a bcc-Al, was formed by ultrafast microexplosion. Formation of new phase of aluminium within the compressed sapphire provides evidence of unusual and unexpected phenomenon, namely, the spatial separation of Al- and O-ions at the plasma stage and then freezing the bcc-Al nanocrystals during the transition to ambient conditions. The analysis reveals that spatial separation of ions with the different masses is possible in highly non-equilibrium, hot, dense and short-lived plasmas, where the temperatures of electrons and ion species are significantly different. The essential distinctive feature of laser-driven microexplosion is that the modified material remains compressed and confined in a strongly localized region inside a bulk, and can be investigated later by Raman spectroscopy, electron beam, x-ray, and other structural diagnostics techniques.
We currently concentrate on the intense focused pulse propagation in transparent dielectrics accompanied by gradually increasing ionisation non-linearity, which changes the profile and spectrum of the pulse. We also study the fundamental processes during fast dramatic transformation of a solid into the dense plasma state of WDM under the action of short intense pulse. In future studies we plan to generate TPa and to expand the studies of structural modification to opaque materials buried under the transparent layers, and to develop pump-probe technique for observing in situ the process of the microexplosion in real time with fs-temporal resolution.
Figure: Electron microscope images of laser produced voids beneath the SiO2 surface of the oxidized wafer. (a) SEM image of FIB-opened section showing an array of voids produced by 170 fs, 800 nm, 300 nJ single laser pulses focused 2μm apart with ×150 objective; the inset shows a magnified transverse crosssection of voids. (b)–(d) TEM side views of voids at the Si/SiO2 interface produced by single 400 nJ pulses focused with ×20 objective to 2 J/ cm−2 (c) and with ×150 objective focused at 42 J cm−2 (c) and 95 J cm−2 (d). The TEM images (b)–(d) demonstrate the elongation of voids toward the laser pulse with an increase of laser fluence, starting from the Si–SiO2 interface at 2 J cm−2 just above the threshold of optical breakdown.
- E. G. Gamaly, L. Rapp, V. Roppo, S. Juodkazis and A. V. Rode, “Generation of high energy density by fs-laser induced microexplosion confined inside a solid” New Journal of Physics in press (2013).
- E. G. Gamaly, A. Vailionis, V. Mizeikis, W. Yang, A. V. Rode, S. Juodkazis, “Warm Dense Matter at the bench-top: Fs-laser-induced confined micro-explosion” High Energy Density Physics, 8, 13-17 (2012)
- R. Buividas, G. Gervinskas, A. Tadich, B. C. C. Cowie, V. Mizeikis, A. Vailionis, D. de Ligny, E. G. Gamaly, A. V. Rode, S. Juodkazis “Phase Separation in Laser-InducedMicro-Explosion in Olivine(Fe,Mg)2SiO4” in press, Optical Materials Express (2013)
- A. Vailionis, E. G. Gamaly, V. Mizeikis, W. Yang, A. V. Rode, S. Juodkazis, “Evidence of superdense aluminium synthesized by ultrafast microexplosion” Nature Communications 2, 445 (2011)
- L. Bressel, D. de Ligny, E. G. Gamaly, A. V. Rode, S. Juodkazis “Observation of O2 inside voids formed in GeO2 glass by tightly-focused fs-laser pulses”, Optics Materials Express 1, 1150-1157 (2011)
- E. G. Gamaly, L. Rapp, V. Roppo, S. Juodkazis and A. V. Rode, Generation of high energy density by fs-laser-induced confined microexplosion, New J. Phys. 15, 025018 (2013).