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Effects of spatial beam coherence and plasma scale length on stimulated Raman scattering and two-plasmon decay

Chiharu Nakatsuji1,*, Yuji Takagi1, Gabriele Cristoforetti2, Sota Matsuura1, Takuya Honda1, Daisuke Tanaka1, Dimitri Batani3, Takumi Sato1, Shun Horimoto1 et al.

Hideo Nagatomo1, Yasuhiko Sentoku1, Philippe D. Nicolaï3, Kai Taketoshi4, Naoki Yamagata4, Norimasa Ozaki4, Yasunobu Arikawa1, Akifumi Yogo1, Shinsuke Fujioka1, and Keisuke Shigemori1,†

  • *Contact author: nakatsuji.chiharu.ile@osaka-u.ac.jp
  • †Contact author: shigemori.keisuke.ile@osaka-u.ac.jp
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Phys. Rev. E 114, 015202 – Published 6 July, 2026

DOI: https://doi.org/10.1103/ppxh-562y

Abstract

We present an experimental investigation demonstrating that the suppression of parametric instabilities in laser-plasma interactions under conditions relevant to direct-drive inertial confinement fusion, specifically backward stimulated Raman scattering (SRS) and two-plasmon decay (TPD), shows the effects of spatial beam coherence and plasma-density scale length. Experiments were performed with the GEKKO-XII kilojoule laser, both with and without random phase plates. Results indicate that SRS suppression is enhanced under conditions of initial spatial incoherence, whereas TPD is influenced primarily by the plasma scale length. A comparison of the relationship between the SRS and TPD signals and hot-electron measurements suggests that TPD is the primary source of hot electrons across all experimental conditions. These findings underscore the importance of beam coherence in determining instability dominance and carry implications for mitigating hot-electron preheat in ignition-scale inertial-confinement implosions as well as for developing hot-electron-driven schemes such as shock ignition.

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Outline

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Phys. Rev. E 114, 015202– Published 6 July, 2026
  • Received 21 August 2025
  • Revised 29 April 2026
  • Accepted 9 June 2026
Article part of CHORUS
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