Diagnostics for precise target positioning in ~10^22 W/cm2 laser-plasma experiments
preprint
posted on 2023-06-09, 07:00 authored by Evgeny Vishnyakov, Akito Sagisaka, Koichi Ogura, Tatiana Pikuz, C Armstrong, Sergey Pikuz, Bruno Gonzalez-Izquierdo, Timur Esirkepov, Wenchao Yan, Tae Moon Jeong, Sushil Singh, Prokopis Hadjisolomou, Ondřej Finke, Gabriele Maria Grittani, Michal Nevrkla, Carlo Maria Lazzarini, Andriy Velyhan, Takehito Hayakawa, Yuji Fukuda, James Koga, Masahiko Ishino, Kotaro Kondo, Yasuhiro Miyasaka, Akira Kon, Masaharu Nishikino, Evgeny Nosach, Danila Khikhlukha, Ilia Tsygvintsev, Deepak Kumar, Jaroslav Nejdl, Daniele Margarone, Pavel Sasorov, Stefan Weber, masaki kando, Hiromitsu Kiriyama, Yoshiaki Kato, Georg Korn, Kiminori Kondo, Sergei Bulanov, Tetsuya Kawachi, Alexander PirozhkovTight focusing with very small f-numbers is necessary to achieve highest at-focus irradiances. However, tight focusing also means short Rayleigh length, which imposes strong demands on the precise positioning of the target at the best focus to achieve the highest on-target irradiance. We describe several near-infrared, visible, ultraviolet, soft and hard X-ray diagnostics employed in the ~10^22 W/cm2 laser-plasma experiment at the J-KAREN-P laser facility in KPSI, Japan. The experiment requires a tight focusing of ~10 J femtosecond infrared laser pulses into ~1.3-µm-diameter focal spots on stainless steel (SUS) solid targets of different thicknesses (5–20 µm). We discuss the applicability of these diagnostics to determine the best in-focus position of the target with <10 µm accuracy (i. e., within the short Rayleigh length) in high-power laser-matter experiments, and suggest which diagnostics should and which ones should not be used for this purpose. It was demonstrated that the target could be positioned to within few µm out of the best laser focus, ensuring over 80% of the ideal peak intensity.