Nanotechnologies / Materials
Nanotechnology, Medical & healthcare, Food industry

Development of ultrafast electric field measurement around electric beam and charged particles~First experimental demonstration of relativistic Coulomb electric field contraction~
Institute of Laser Engineering
Associate Professor Makoto Nakajima
https://researchmap.jp/nakajimamakoto?lang=en

Nanotechnologies / Materials

Abstract
We developed the evaluation method of ultrafast spatio-temporal
distribution of electric field around electron beam and charged
particles using the electro-optic sampling technique. We succeeded in observing ultrafast dynamics of the electric field by single
shot detection method. We demonstrated the first observation of
the contraction of the Coulomb electric field by the electron beams
moving at close to the speed of light. The contraction of the Coulomb electric field observed this time is a fundamental phenomenon predicted by the theory of special relativity, and we succeededin observing the electric field contraction process experimentallyfor the first time (see Figures 1 and 2, Papers 1,2). This developed
method is very powerful in evaluating the spatio-temporal profile ofthe electron beam itself and the electric field around it.

▍ Background & Results
Technologies for generating electron beams, charged particles,etc. are rapidly improving, and pulsed light sources in the picosecond and femtosecond range are also being developed. The evaluation methods of the profile of electron beam and the spatio-temporal distribution of the electric field are demanded. This time wedeveloped the single shot evaluation method with the step-like mirror of echelon. Figure 1 show the image of the formation processof the relativistic electric field contraction that accompanies thepropagation of a near-light-speed electron beam. Figure 2 shows
the observed spatio-temporal distribution of the Coulomb electricfield which shows relativistic contraction clearly. This electric field
contraction is the fundamental phenomenon predicted by the special relativity by Einstein over 100 years ago. We demonstrated itexperimentally for the first time. The distribution of contracted electric field is perpendicular to the propagation direction of the electron bunch. This evaluation method is very powerful and provide
the information on spatio-temporal distribution of the electric field
in ultrafast time scale by the single show detection. From the distribution, we can obtain also the information on the electron beamprofile in spatio-temporal dimension [See the paper 1,2 as shown
below].

Figure 1 Image of the formation process of the relativistic electric field contractionthat accompanies the propagation of a near-light-speed electron beam (shown as
an ellipse in the figure)▍ Significance of the research and Future perspective
Electron beams and charged particles are expected to be used
in applications, not only in medicine but also in applications thatutilize electron beam exposure technology for nanotechnology andsemiconductor industry, and sterilizing effects for food industry.
Our method can evaluate the spatio-temporal distribution of theelectric field in ultrafast time scale with the single shot detection.
This research result demonstrates the fundamental phenomenon of
special relativity in electromagnetism proposed by Einstein. But it
can also be used to evaluate the pulse characteristics of electron
beams and charged particles, and is very useful for developing
applications based on the electron beams as an essential tool forthe evaluation.

Figure 2 Observed spatio-temporal image of the relativistic contraction of Coulomb electric field around an electron beam moving at close to the speed of lightP a t e n t Japanese Patent Application No.2021-106147
Ota, Masato; Nakajima, Makoto et al. Ultrafast visualization of an electric field under the Lorentz transformation. Nature Physics. 2022, 18, 1436-1440.
doi: 10.1038/s41567-022-01767-w
Ota, Masato; Nakajima, Makoto et al. Longitudinal and transverse spatial beam profile measurement of relativistic electron bunch by electro-optic
Tr e a t i s esampling. Applied Physics Express. 2021, 14, 026503. doi: 10.35848/1882-0786/abd867
Arikawa, Yasunobu; Nakajima, Makoto et al. The conceptual design of 1-ps time resolution neutron detector for fusion reaction history measurement atOMEGA and the National Ignition Facility. Review of Scientific Instruments. 2020, 91, 063304. doi: 10.1063/1.5143657
URL https://resou.osaka-u.ac.jp/en/research/2022/20221021_1
K e y w o r d EO sampling, electron beam, terahertz, coulomb electric field contraction, special relativity