23T-1
Front Edge of High Energy Density Science with High Power Laser
パワーレーザーによる高エネルギー密度科学
Ryosuke Kodama
兒玉了祐
Photon Pioneers Center and Graduate School of Engineering, Osaka University
2-1, Yamadaoka, Suita 565-0871, Japan
大阪大学 〒565-0871 吹田市山田丘2-1
High Energy density states created by high power lasers cover a variety of attractive fields of sciences andtechnologies such as particle acceleration, laboratory astrophysics, and material science, nuclear science
including medical applications and laser fusion. Two novel states with high energy density are now being
explored in both vacuum and sold with high power lasers, i.e. nonlinear optics in vacuum and high energy
density solid matter such as solid metallic hydrogen. These new fields will be opened by well controllingof high energy density plasmas.

1. Introduction
High power laser technologies are now opening avariety of attractive fields of sciences andtechnologies using high energy density plasmas.
The high energy density plasmas created by highpower lasers include a lot of states of plasmas asshown in Fig.1, e.g. warm dense matter, highpressured plasmas, radiative plasmas, fusion
burning plasmas, relativistic plasmas andelectro-positron plasmas. These broad areas ofplasmas enable us a lot of applications of highenergy density plasmas such as particle acceleration,
laboratory astrophysics, material science, nuclear
science including medical applications and laser
fusion, which are “High Energy Density Science(HEDS). These applications are well in progresswith technologies on high power lasers and related
plasma devices [1-4].
On the other hand, novel states with high energy
densities are now being created in vacuum or as asolid by controlling of high energy density plasmas
as well as high power lasers. These states areshown in the areas out of the plasma states as show
in Fig.1, which would be key elements to open new
fields of sciences. The nonlinear optics in vacuum
will be experimentally realized with developmentof novel focusing optics or a spheroid plasma
mirror [5] as well as 100PW lasers. Calculating
Lagrangian densities of electromagnetic fields withquantum electromagnetic dynamics (QED) andwave optics, feasibility of experiments are
discussed on nonlinear optics in vacuum. Otherinteresting topics are creation and freezing of highenergy density solid states with high power lasers.
A metallic state of Silicon existing at an ambientpressure has been created at a few 10GPa with afast compression scheme using high power lasers,

for the first time. In the TPa regime of pressures attemperatures of less than 8000K, we havedemonstrated creation of a super diamond or BC8
carbon, which must have twice of densities ofdiamond. As an ultimate goal of exploring of thehigh energy density solid matter and material,
element technologies are being developed to createa solid state of metallic hydrogen at temperatures ofless than a few 1000K with pressures of aroundTPa.

Fig.1. Phase diagram showing high energy density
plasma states accessible with high power lasers.
The circles i.e. high energy density solid andnonlinear optic in vacuum are now being exploredby control of the high energy density plasmas.

2. Nonlinear Optics in Vacuum
According to the uncertainty principle, vacuum
has quantum fluctuations and photons can interact
with vacuum. Classical analogy of the quantum
fluctuation with special relativity may allow us toimagine virtual particles for a short time in vacuum.
Intense laser light could interact with the virtualparticles, resulting in nonlinear optics in vacuum
and vacuum breaking with avalanche phenomena.
The nonlinear optical properties before break of
vacuum or creation of real particles can be treatedwith QED and perturbation theory. From thisanalysis, dipoles in vacuum are excited by both ofelectric field and magnetic field. The polarization
and beam pattern after the interaction in vacuum aretotally different from those in matter. As otherinteresting points different from the interaction withmater, the interaction rate significantly depends on
the angle of the laser beams or a focusing coneangle [6]. To realize experiments on the nonlinear
optics in vacuum, we have developed a novel
geometry of a plasma mirror [5], which realizes fast
focusing of laser light with cone angles of morethan 100deg in a large laser system. By using
such a plasma photonic device, we would open
nonlinear optics in vacuum at laser powers of lessthan 100PW.

Fig. 2. Image of laser interaction with vacuum
3. High Energy Solid States
High power lasers also easily generate highpressures of more than TPa. This high pressure
condition creates a strong shockwave in matter.
The shockwave followed by a Hugoniot relation has
been a useful tool to investigate EOS of highpressured matter. The pressures of more than
0.1TPa is the energy density corresponding to thechemical bonding energy, resulting in expectationof dramatic changes in the chemical reactions.
At pressures of more than TPa, most of material
would be melted on the shock Hugoniot curve.
However, if the temperature is less than 1eV orlower than a melting point at pressures of more thanTPa, novel solid states of matter must be createdthrough a pressured phase transition. One of theinteresting materials must be carbon. The structureof the carbon is well known as a diamond atpressures of more than about 10GPa. At pressuresof more than TPa, the diamond structure changes to
BC and cubic at more than 3TPa. The band gap of
the cubic structure carbon could disappear anddiamond semiconductor changes to a metallic. On

the other hand, the BC8 carbon will be stillsemiconductor and harder than the conventional
diamond. Then it is called as “Super-diamond”.
To create such novel states of matter, several
kinds of isentropic-like compression techniques arebeing developed with high power lasers, e.g.
impedance matching, pulse tailoring, staticdynamic coupling compression and hybridcompression. The super diamond phase has beenrealized with a ns high-power laser using theimpedance matching technique for the first time.
One of other important compression techniques isnon-equilibrium compression or fast compression.
Using this technique, high pressured states of Si,
which was metallic state, was kept at ambientpressures. Detail mechanisms of the freezing of
the high pressured states have been not yet cleared
but metallic Si confidentially exists on our hand at
ambient pressures. This result indicates that morekinds of matters, which had been realized only athigh pressure conditions, would be expected asnovel material.
Extending the metallization of the material with
the isentropic compression, superconductive
metallic hydrogen must be the ultimate. Once thesolid metallic hydrogen was generated, the Deby
temperature was extremely high and it would bestrongest material against thermal fluctuations. Thisis because the monatomic solid hydrogen canpossess high number density due to no closed shellelectrons and nuclear mass is much lighter thanother material.
4. SummaryHigh energy density plasmas are being exploredwith high power lasers. Novel states with highenergy densities i.e. nonlinear optics in vacuum andhigh energy density solid matter/material are now
being created by well control of high energy density
plasmas as well as high power lasers.
AcknowledgmentsThese works are supported by JST-CREST,
JSPS-KAKENHI(S) and MEXT photon science andtechnology network project.
References[1] R. Kodama et al.: Nature 412(2001) 798; Nature 418(2002) 933.
[2] Gr : Nature Phy. 2 (2006) 456.
[3] T. Hosokai et al.: Appl. Phys. Lett.
[4] R. Kodama et al.,: Nature 432 (2004) 1005.
[5] M. Nakatsutsumi et al., Opt. Lett. 35 (2010) 2314.
[6] Y. Monden and R. Kodama, Phys. Rev. Lett. 107(2011) 073602.