Study of dynamical extreme ultraviolet radiation driven material interactions

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K03893
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 14010:Fundamental plasma-related
• Research Institution: Osaka University
• Principal Investigator: Tanaka Nozomi 大阪大学, レーザー科学研究所, 特任助教(常勤) (60581296)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 極端紫外(EUV)光 / 光電離プラズマ / 物質アブレーション / 分光計測

Outline of Final Research Achievements

The mechanism and characteristics of photoionization/photodissociation hydrogen plasma produced by intense extreme ultraviolet (EUV) light were investigated by using a laser produced plasma (LPP) EUV light source. Visible spectroscopy and laser-induced fluorescence methods obtained the electron density, electron temperature, and the population density of hydrogen atoms for each orbital state. The population density showed good agreement with a collisional radiative model, indicating that continuous ionization and recombination are the main processes of plasma formation, and that the plasma is in a quasi-steady state. Further, 1D radiation hydrodynamic simulation showed that the emission spectrum of the LPP can be controlled, having peak from vacuum ultraviolet down to EUV, by controlling the drive laser intensity in the range of 1E9-1E11 W/cm2. Thus, we can selectively produce photoionized hydrogen plasma at high intensity, and photo-dissociated hydrogen atoms at low intensity.

Free Research Field

極端紫外光応用

Academic Significance and Societal Importance of the Research Achievements

本研究ではデータベースが豊富であり、モデル化が比較的容易な水素を対象とすることでプラズマ生成メカニズムから特性までを明らかにすることができた。短波長光照射による光電離プラズマは生成過程や特性がレーザーアブレーションプラズマとは大きく異なることから、例えばWarm dense matterなどの特殊な状態として学術的な研究意義が深い。一方EUV光照射による光電離水素プラズマはEUVリソグラフィ光源内に存在し、受動的ではあるが汚染除去に用いられている。本研究はEUV光源における水素プラズマの特性、そして汚染除去に向けた最適化の制御ノブを示したことに大きな社会的意義がある。