2022 Fiscal Year Annual Research Report
Investigation of early-time dynamics of laser-produced carbon plasma by collective Thomson scattering
| Project/Area Number |
22J12063
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| Allocation Type | Single-year Grants |
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| Research Institution | Kyushu University |
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Principal Investigator |
PAN Yiming 九州大学, 総合理工学府, 特別研究員(DC2)
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| Project Period (FY) |
2022-04-22 – 2024-03-31
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| Keywords | トムソン散乱 / レーザープラズマ / プラスマ計測 |
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| Outline of Annual Research Achievements |
Laser-produced plasma (LPP) has been studied for over 50 years due to its relevance to several prominent scientific and industrial applications, such as inertial controlled fusion and extreme ultraviolet lithography (EUVL) for semiconductor manufacturing. Therefore, understanding the LPP characteristics during the laser irradiance is of great research interest. However, experimental studies on LPP dynamics during and soon after (< 50ns) the laser irradiance have never been performed. The major reason for this is that LPP is highly non-uniform and changes rapidly in both space (within tens of micrometers) and time (within nanoseconds), making the early LPP dynamics unclear.
For the first time, we have demonstrated that such investigations are possible by utilizing the collective Thomson scattering method (CTS). It provides highly spatial and temporal resolved plasma parameters (electron density, electron temperature, and velocity field) of carbon LPPs in a 2-dimensional space, at the time delay of 0 to 14 ns after the laser peak. Additionally, we performed a 2D radiation hydrodynamic simulation under identical conditions as those used in the experiments. Therefore, the results allow for a first test of existing theoretical models and simulation codes. We found that the 1-dimensional isothermal model could better describe the LPP expansion at this early stage, rather than the well-accepted adiabatic model.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
As originally planned, the specialized spectrometer for this research has been developed and tested to achieve the expected performance. The stray light has been successfully reduced to 1/10000, and the measurable region has been expanded to 1.5 mm in the Y-direction and 1 mm in the Z-direction.
With this spectrometer, I successfully measured the plasma temperature, density, and flow velocity in laser-produced carbon plasma using the Collective Thomson scattering method, during and just after laser irradiation. These results were measured at time delays of 0, 4, 9, and 14 ns after the laser peak and at distances of 130 to 600 μm above the target surface. These spatially and temporally resolved results reveal a clear evolution history of LPP expansion dynamics.
In addition, we performed 2D radiation hydrodynamic simulations under identical conditions as those used in the experiments. By comparing the results with existing theoretical models and the radiation-hydrodynamics code STAR, we obtained some important new insights into LPP dynamics at this early stage.
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| Strategy for Future Research Activity |
With the detailed investigation of the time window soon after the drive laser peak completed in the first year, the focus of the second year will shift to the study of LPP dynamics during laser irradiance. This is crucial because LPPs emit short-wavelength emissions only during the laser pulse, which is of great importance for several scientific and industrial applications. The ablation laser pulse is 7ns in FWHM, a 2ns resolution (decided by the ICCD gate) should be sufficient for the investigation. If it is necessary, the probe laser will be compressed by Stimulated Brillouin scattering (SBS), to compress the nanosecond probe pulse into several hundred picoseconds.
Several target materials, ranging from light (e.g., C, Al) to heavy (Sn, Gd, W), will be studied under various laser conditions. Utilizing CTS, a two-dimensional view of the plasma parameters for all these materials will be obtained, providing new insights into the relationship between laser intensity and electron temperature. This information is crucial for the development of state-of-the-art and next-generation extreme ultraviolet lithography (EUVL).
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