Institute of Laser Engineering, Osaka University

Nuclear Photonics (NP)

Summary

Nuclear Photonics is the new field of science born in 2010. The NP group at ILE established in April 2018 to explore this new area by developing unprecedented academic research and industrial applications by inducing nuclear reactions using laser technology. In order to achieve this extreme condition, high power lasers are used to generate (high-energy X-ray / γ-ray) or secondary particles (ion/electron).

Therefore, the NP group is promoting a wide range of research areas from industry to academia such as astrophysics through our key technology: Nuclear Photonics.

Group website

Research Content

Laser-driven ion acceleration

The interaction of high power laser with a target at a thickness of 10s of nanometer to 100s of micrometer (about the cross-section of the hair) in an extremely short time scale (about 1 trillionth of a second) leads to the production of strong electromagnetic fields. This field can be used to accelerate ions at tens of MeV (million electron volts) in very short distances (tens of microns). Until now the ion acceleration has been done only using conventional acceleration method at significantly larger sizes, but now with the current trend in the development of high power lasers, this field of science is evolving.

The NP group at ILE explores different techniques and mechanisms to enhance the ion generation and acceleration via Target Normal Sheath Acceleration (TNSA) and Radiation Pressure acceleration (RPA). At TNSA, the interaction of lasers at intensities of (>1018 Wcm-2) creates hot electrons population with an energy of approximately similar to the ponderomotive force of the laser at its focus. As a result, the electrons propagate through the target into the vacuum and produce a sheath field at the rear side. As the target becomes positively charged (due to the escaping electrons), a sheath field is generated, which leads to the acceleration of ions. On the contrary to TNSA which acceleration occurs at the rear side, RPA works with intensities of (>1021 Wcm-2) when the whole plasma accelerates at whole by means of light pressure.

In addition to the mechanisms mentioned above which are currently in development, the NP group aims to explore a mechanism that gives hints to the cosmic phenomena.

Laser-driven neutron source

The generation of mult-MeV ion beam has produced a clear path towards the development of fusion neutron sources. The neutrons are produced from the interaction of ions (e.g. protons, deuterons) generated from the target (known as pitcher) with a converter (known as catcher). These neutrons are above 100s of KeV in temperature known as fast neutrons. They have a high penetration capability and ability to extract information from the medium they are travelling in. Here at ILE, the NP group develop neutron sources that can be used for different applications from non-destructive evaluation to imaging, healthcare and science. These sources are extremely short in time, about sub-picosecond (one billionth of a second) compared to millisecond sources in nuclear reactors and microsecond sources such as spallation facilities.

Development of Extreme Ultra Violet (EUV) light source and its applications

We study both the fundamental and applied science of extreme ultraviolet (EUV) interaction with matter to develop novel materials processing methods which can lead to biomedical or semiconductor devices. The EUV wavelength ranges from few to few tens of nanometers. The interaction process of photon and matter in this wavelength range shows unique properties. The light is strongly absorbed within depths of few tens to few hundreds of nanometers from the surface. Further, its high photon energy ~100 eV exceeds the band gap energy of many upcoming wide-band-gap (WBG) materials, leading to single photoionization of inner orbital electrons.

Our laser produced plasma (LPP) pulsed EUV source at ILE Osaka university provides nanosecond pulses of mJ range of EUV light, and the EUV focusing optics enables us to irradiation of either intense or high-fluence EUV light onto materials.

We have shown possibilities to modify surface structures and create near-surface interfaces of nanoparticle supported polymer materials by depositing EUV photon energy exclusively into shallow area from the surface. Further, our interest is not only limited to surface treatment studies, but also “EUV ablation physics”. It is recently attracting much attention in both physics and technology fields. The ablation mechanism and characteristics of plasma of EUV ablation are completely different from that of conventional laser ablation at longer wavelength. We have experimentally shown difference of some of plasma properties, such as ion abundance or expansion geometry, between EUV ablation and laser ablation.

Member

Akifumi Yogo Associate Professor (Group Leader)
Seyed Reza Mirfayzi Specially Appointed Assistant Professor
Nozomi Tanaka Researcher
Hiroaki Nishimura Specially Appointed Professor
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