「様式３」P-44

Imaging of laser-induced microexplosions in dielectrics using
time-resolved X-ray diffraction technique[1] Organization
Leader：D. Arturas Vailionis(Stanford Nano Shared Facilities, Geballe
Laboratory for Advanced Materials)
Representative：Prof. Vygantas Mizeikis(Research Institute of Electronics, ShizuokaUniversity, Japan)
Participants：
Prof. Akira Saito(Division of Precision Sci. & Technology andApplied Physics, Graduate School ofEngineering, OSAKA University, Japan)
Prof. Atsushi Ono(Research Institute of Electronics, ShizuokaUniversity, Japan)
Prof. Saulius Juodkazis (Centre of Microphotonics,Swinburne University of Technology, Melbourne,Australia)[2] Research progressThis joint research project pursues studies of the time
dynamics of the formation of novel phases and time
evolution of warm dense matter in conditions of ultrahighpressures and heating/cooling rates (1-10 TPa and 1017
K/s) created by a confined micro-explosion inside
sapphire single crystal. In order to follow the time
evolution of states of matter from hot solid-density plasma
to a formation of novel metastable materials, theexperiment must utilize synchronized ps laser pump beamand ps hard x-ray probe beam. The ps laser pump withenergy of ~100 nJ tightly focused inside Al2O3 single
crystal transforms sub-micron volume of material to solid
plasma which then explodes and generates a powerfulshock wave. The subsequent variable time-delayed hard
x-ray probe probes time-dependent structural evolution ofhighly compressed surrounding material. The obtained
data would shed a new light on the time evolution of newmetastable phases that are formed after laser-generated
shock wave inside Al2O3 single crystal matrix. A deeper
knowledge of the conditions that lead to synthesis ofsuper-dense and super-hard materials, and how this stateof matter can be “frozen” during the ultrafast transition to
the ambient conditions, can be obtained as a result of theseexperiments.
[3] Results(3-1) Research results
The above experiments require deep multi-disciplinary
insight into various physical and chemical phenomena,such as intense laser pulse-matter interactions, formationof warm dense matter (WDM) state, X-ray
crystallography, and synchrotron beam transient
diffraction. The results obtained during previous
collaborative studies show that extreme pressures andtemperatures can be created with tabletop setup using
ultra-short laser pulses tightly focused inside transparent
material. Such setup was previously used to createhigh-pressure bcc-Al phase “frozen” inside sapphire single
crystal which was identified by x-ray microdiffraction at
the Advanced Photon Source, Argonne National
Laboratory (ANL), USA.
The previous X-ray diffraction (XRD) experiments wereused to probe the laser-irradiated sapphire understeady-state conditions, i.e., when all transientmodifications resulting from the ultrashort laser pulse
irradiation became extinct. Here, we aim to extend ourprevious investigations into the realm of transientmodification. For this purpose, a series of time-resolvedexperiments intended to be carried out at ANL werecarefully designed by the participants of this project. In
order to promote collaboration on these topics, a mini
workshop entitled “Applications of Infrared, Visible, andX-ray Beams for Fabrication and Imaging ” wasorganized on February 1, 2016 at the Research Institute ofElectronics, Shizuoka University. The workshop wasattended by participating researchers, as well as interested
guests and students. Presentations and discussions during
the workshop were centered on the following topics:
A. Development of detailed plan for time-resolved XRD
experiments

Fig. 1. Time-resolved XRD experiment. X-ray pulse
delayed by a variable time with respect to the laser pulse
probes transient state of WDM created by the latter.
Depending on the delay, different XRD patterns
reflecting the transient state can be registered. To ensurethat fresh regions of the material are always probed, thesample is translated by a sufficient distance between two
subsequent laser shots.

The proposed experiment is shown schematically in Fig. 1.
Time-resolved XRD will use thin slabs of sapphire(80-100 μm, thick) in order to ensure high transparency toX-rays. Length of the slab will be large enough to ensuresufficient amount of new undamaged crystal for each newlaser shot when the sample is moved between thesubsequent laser shots.
The experiments will be performed using a Ti:sapphire
amplified laser system and an X-ray probe beam at one of
the available beam lines. In order to tightly focus
ultra-short laser spot within sub-micron volume ofsapphire crystal, a microscope lens will be used. The
requirements for the X-ray beam, optical setup, laser andthe sample stage are as follows:•••

Pump laser: wavelength 800 nm (or 400nm),
pulse duration 1.2 ps, energy up to 10 mJ/pulse;
optical microscope focusing using high NA
optics to create a tight focusing spot inside
crystal to ~ 0.4-0.8 μm in diameter (FWHM);
X-ray probe: polychromatic pink beam; ~ 1 µm
focal spot desirable (larger size would bedesirable);Nano-positioning stage with ~0.1 µm accuracy
along xyz axes

The experiment will be carried out as a pump-probe

experiment. The x-ray delay time will be varied from 100
fs to 10 ns in accordance to the expected timescale of thetransient physical processes in the sample, inferred fromthe previous experiments, theoretical analysis, and theavailable literature. It is expected that XRD pattern will
depend on the delay between the optical and X-ray pulses.
This setup will allow to study formation and time
evolution of WDM created by confined micro-explosionin conditions of extreme pressures and record highheating/cooling rates where the hot solid density plasma
forms and transforms into new crystals during several
nanoseconds.
It is expected that transient XRD will reveal the following
important stages of the laser-induced modification insapphire:• Hot, solid density, high-pressure (TPa) plasma,time duration ~ 2 ps, temporal resolution~10-100 fs. Scattering spectra, aiming for
observing density and temperature deviations of
the initial stage of micro-explosion;• Second stage of generation of shock wave andformation of void (~ ns) –scattered X-ray spectrawith amorphous and crystalline features;
temporal resolution ~10 ps;• Shock wave propagation and stopping, coolingand crystal stabilization in 10-20 ns.
Observation of a new crystal/amorphous stages
formation, temporal resolution 100 ps;
B. Steps necessary for practical realization of the proposed
experiments
In order to carry out these experiments, access to a relevantbeam line at the Advanced Photon Source of ANL is themost important. For this purpose, a General user proposal(GUP) entitled “Time-dependent characterization ofWarm Dense Matter created by laser-induced
microexplosion” intended for the beam line time
application was worked out during the mini-workshop andafterwards. Main idea of this proposal follows theprinciples described above. Particular details discussed
between the participants and included into the plan also
involved the necessary preparatory steps, and actions of
the participants during the experiments. At the moment of
this writing, the GUP has already been submitted forreview.
(3-2) Ripple effects and further developments
Exchange of scientific expertise between the participants

was very helpful for coordination of experimental andtheoretical work towards the goal of this project. Also, it
has contributed to strengthening of domestic andinternational collaboration at Research Institute ofElectronics.
It must be also stressed that joint work of all participants
during the mini-workshop and informal discussions
have broadened the scope of existing domestic andinternational research collaborations at RIE, as well asopened new venues for collaboration in the future.

[4] Achievements
List of publications:(1) M. Malinauskas,A. Zukauskas,Y. Hasegawa,V.
Hayasaki,V. Mizeikis, R. Buividas, S. Juodkazis,“Ultrafast laser processing of materials: from science toindustry”, Light: Science & Applications , accepted(2016).

Travelling report
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Dr. Arturas Vailionis
Stanford Nano Shared Facilities, Geballe Laboratory for Advanced Materials
2016.01.30-02.02
Shizuoka University, JapanTo carry out a joint research, plan the future collaboration, participate at the mini-workshop andreport previously obtained results.
Prof. Vygantas Mizeikis
Prof. Akira Saito
Division of Precision Sci. & Technology and Applied Physics, Graduate School of Engineering,Osaka University, Japan
2016.01.31-02.02
Shizuoka University, JapanTo carry out a joint research, plan the future collaboration, participate at the mini-workshop andreport previously obtained results.
Prof. Vygantas Mizeikis