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SUMMARY:Material modification at Megabar pressures with ultrashort laser p
 ulses - Professor Andrei Rode\, The Australian National University
DTSTART:20190610T100000Z
DTEND:20190610T110000Z
UID:TALK126241@talks.cam.ac.uk
CONTACT:Joseph Nelson
DESCRIPTION:Ultrashort laser pulses focussed down to a micron-size spot su
 bsurface of transparent materials can achieve energy densities on the orde
 r of MJ/cm3\, resulting in solid-density plasma formation\, followed by a 
 microexplosion and shockwave compression of the surrounding substance. Sub
 sequent rapid quenching leads to the formation and preservation of novel n
 on-equilibrium material states. Reaching extreme pressures is of fundament
 al interest for the formation of new material phases\, and also for the st
 udy of the Warm Dense Matter\, reproducing the state of the cores of plane
 ts in table-top laboratory experiments.\n\nUltrafast laser induced microex
 plosion in confined geometry has already demonstrated the potential to cre
 ate and preserve new thermodynamically non-equilibrium state of matter suc
 h as bcc-Al [1] and two tetragonal phases of Si [2].  These new phases hav
 e been predicted to exist theoretically\, but have never before observed i
 n nature or in laboratory experiments. In this talk I’ll present a new w
 ay for increasing the shock wave affected volume by using a micro-Bessel b
 eam with a 100:1 aspect ratio [3\,4]. The experimental results show an eff
 ective formation of voids when such a beam focused inside sapphire crystal
 \, which is a clear indication of significantly increased efficiency of ne
 w phase formation when compared with the previous experiments with a Gauss
 ian laser beam. The results open up a new way for increasing the quantity 
 of high-density/pressure phases and help to increase sensitivity in search
  of new phases using X-ray and electron diffraction analysis.\n\n[1] A. Va
 ilionis _et al_.\, “Evidence of superdense aluminium synthesized by ultr
 afast microexplosion”\, "Nat. Comm. *2*\, 445":https://www.nature.com/ar
 ticles/ncomms1449 (2011). \n\n[2] L. Rapp _et al_.\, “Experimental evide
 nce of new tetragonal polymorphs of silicon formed through ultrafast laser
 -induced confined microexplosion”\, "Nat. Comm. *6*\, 7555":https://www.
 nature.com/articles/ncomms8555 (2015).\n\n[3] L. Rapp _et al_.\, “High a
 spect ratio micro-explosions in the bulk of sapphire generated by femtosec
 ond Bessel beams”\, "Sci. Rep. *6*\, 34286":https://www.nature.com/artic
 les/srep34286 (2016).\n\n[4] E. G. Gamaly and A. V. Rode\, “Ultrafast re
 -structuring of the electronic landscape of transparent dielectrics: new m
 aterial states (Die-Met)”\, "Appl. Phys. A *124*\, 278":https://link.spr
 inger.com/article/10.1007/s00339-018-1693-3 (2018).\n
LOCATION:Goldsmiths 1\, Lecture Theatre\, Department of Materials Science 
 & Metallurgy
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