24E02
Inverse Compton Scattering from Laser accelerated electrons andits application for Stand-off Detection III
レーザー加速電子によるレーザー光の逆コンプトン散乱エックス線発生と	 遠隔透視応用III	 	 
Yoshitaka Mori1, Hajime Kuwabara2, Katsuhiro Ishii1, Ryohei Hanayama1,Toshiyuki Kawashima3 and Yoneyoshi Kitagawa1
森	  芳孝1, 桒原	  一2，石井勝弘1，花山良平1，川嶋利幸3，北川米喜1
The Graduate School for the Creation of New Photonics Industries,
Kurematsuchou, 1955-1 Nishi-ku, Hamamatsu 431-1202, JapanIHI Corporation,
Shinnakaharacho 1, Isogoku, Yokohama, Kanagawa, JapanHamamatsu Photonics, K. K.
Kurematsuchou,1820 Nishi-ku, Hamamatsu 431-1202, Japan
光産業創成大学院大学 〒431-1202	  浜松市西区呉松町1955-1
IHI株式会社	  〒431-1202	  浜松市西区呉松町1955-1
浜松ホトニクス株式会社	  〒431-1202 浜松市西区呉松町1820
Interactions between ultra-intense laser and plasma can provide a compact laser-driven electron accelerator. We havedemonstrated inverse Compton X-rays from laser-accelerated multiple quasi-mono energetic electrons. The main laser
beam accelerate electrons to energies of 14 and 23 MeV, which inversely scattered the secondary laser beam into 6 and12 keV X-rays, respectively. This quasi-mono energetic electron has divergence of less than 5 mrad and resulting x-lay
photons have 30o angular distribution. This demonstrates a novel source of monoenergetic directional ultra-short X-ray
pulses in principle. Such directional X-ray can be applied for a stand-off detection in the future.

1. Introduction
Ultra-intense laser technology since 1990s has
contributed rapid progresses in physics oninteractions between ultra-intense photons andplasma. For example, by using laser wake-field
acceleration scheme [1], we can achievemono-energetic electron beams from energy of 10to a few GeV within a few-cm acceleration length[2-4]. Laser-plasma acceleration scheme is now on
the stage for developing its applications. In order tointroduce such innovative technologies into
industrial applications, we have compareddifferences between laser plasma accelerators andconventional RF accelerators. Our conclusion is
movability in the future. Using laser-accelerated
electrons, a novel source of mono-energetic
directional ultra-short X-ray pulses is possible inmobile. This pulse is accomplished by inverse
Compton scattering of laser-accelerated electrons
with energy range of 100 MeV. This novel X-ray
pulse has energy of a few hundred keV, thedivergence within 5 mrad, and the pulse duration ofless than ps. This directional X-ray pulse can beapplied for a stand-off detection in the future. In
which, we can prove the inside of stand-off object
by detecting the back scattering photons from theobject [5]. This manuscript describes present status

of inverse Compton
accelerated electrons.

ScatteringfromLaser

2. Experimental Results
The blue line in Fig. 1 represents the inverseCompton X-ray spectrum calculated from theexperimental electron spectrum. The threecalculated peaks at 5, 13, and 22 keV are derived
from the multiple quasi-monoenergetic peak of theaccelerated electrons; they agree well with theFig.1. Scattered photon spectrum at θ=0: Red points
are experiment data and blue line is calculated from theelectron beam spectrum.

1

Photon Energy [keV]

1000

0.1100θ (Theory)
θ (Exp.)
Ex (Theory)
Ex (Exp.)

101
050
100
150
Electron Energy [MeV]

0.01

0.001
200

Fig.3. Photon energy and divergence of inverse Compton
scattering as a function of electron energy.

Fig.2. Angular anisotropy of inverse Compton scattering:
total number of photons summed over the wholespectrum. Vertical axis is in units of counts/1000 shots.

3. Perspective for stand-off detection
Figure 3 shows the photon energy and divergenceof inverse Compton scattering as a function ofelectron energy. The solid-circle and solid-triangle
are from experiments. The X-ray energy Ex
scattered from the laser photon energy εL is given
from the Klein-Nishina formula [6] by:(1)
E x ~ 4! 2" L
whereγis the Lorentz factor of the electron and εLis 1.55 eV in our experiments. The angle is defined
as 0 in the electron beam direction (i.e., the inverse
direction). The scattering angle θ is also givenby:(2)! ~1/"
when we achieve X-ray beams with energy beyond
200 keV and divergence within 5 mrad at source
point, it becomes 5 cm diameter on the stand-off
object which 10 m apart from the source. Suchbeam is suitable for the application of stand-off
detection for human relief in the disaster field.
In conclusion, the experiments shown here is on
the way to improve the photon energy and beamdivergence of inverse Compton scattering for theapplication of stand-off detection.

Photon Divergence [rad]experimentally observed photon peaks at 6, 11, and19 keV. The peaks at 27 and 34 keV are also likely
inverse Compton signals from higher energy which
beyond our ESM detection range.
Figure 2 shows the angular distribution of inverse
Compton scattering counts. Theory predict thebeam divergence within 2o, however, the data is
spread over 30o. The reason for this may be that theelectron beam is not aligned with an angle of zero
degrees, but it is slightly shifted due to the dipole
magnet. The huge error bar comes from thebackground bremsstrahlung.

Acknowledgments
This work is supported by Grants-in-Aid for
Scientific Research from MEXT #21244088,
2008~2010 Grants of the Science Research
Promotion Fund of the Promotion and Mutual Aid
Corporation for Private Schools of Japan, theGPI-IHI Research Collaboration, as well as
research collaboration with the ILE, Osaka
University #B2-41.
References[1] T. Tajima and J. M. Dawson: Phys. Rev. Lett. 43(1979) 267.
[2] Y. Kitagawa, T. Matsumoto, T. Minamihata, K.
Sawai, K. Matsuo, K. Mima, K. Nishihara, H.
Azechi, K. A. Tanaka, H. Takabe, and S. Nakai:Phys. Rev. Lett. 68 (1992) 48.
[3] E. Miura, K. Koyama, S. Kato, N. Saito, M.
Adachi, Y. Kawada, T. Nakamura, and M.
Tanimoto: Appl. Phys. Lett. 86 (2005) 251501.
[4] W. P. Leemans, B. Nagler, A. J. Gonsalves, Cs.
Toth, K. Nakamura, C. G. R. Geddes, E. Esarey, C.
B. Schroeder and S. M. Hooker: Nature. Phys. 2(2006) 696.
[5] H. Kuwabara, Y. Mori and Y. Kitagawa: J. Plasma
Fusion Res. 3 (2008) 003-004.
[6] V. O. Klein and Y. Nishina: Z. Phys. 52 (1929)
853.