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Sawada H, Sentoku Y, Yabuuchi T, Zastrau U, Förster E, Beg FN, Chen H, Kemp AJ, McLean HS, Patel PK, Ping Y. Monochromatic 2D Kα Emission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism. PHYSICAL REVIEW LETTERS 2019; 122:155002. [PMID: 31050520 DOI: 10.1103/physrevlett.122.155002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 03/10/2019] [Indexed: 06/09/2023]
Abstract
The rapid heating of a thin titanium foil by a high intensity, subpicosecond laser is studied by using a 2D narrow-band x-ray imaging and x-ray spectroscopy. A novel monochromatic imaging diagnostic tuned to 4.51 keV Ti Kα was used to successfully visualize a significantly ionized area (⟨Z⟩>17±1) of the solid density plasma to be within a ∼35 μm diameter spot in the transverse direction and 2 μm in depth. The measurements and a 2D collisional particle-in-cell simulation reveal that, in the fast isochoric heating of solid foil by an intense laser light, such a high ionization state in solid titanium is achieved by thermal diffusion from the hot preplasma in a few picoseconds after the pulse ends. The shift of Kα and formation of a missing Kα cannot be explained with the present atomic physics model. The measured Kα image is reproduced only when a phenomenological model for the Kα shift with a threshold ionization of ⟨Z⟩=17 is included. This work reveals how the ionization state and electron temperature of the isochorically heated nonequilibrium plasma are independently increased.
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Affiliation(s)
- H Sawada
- University of Nevada Reno, Reno, Nevada 89557-0220, USA
| | - Y Sentoku
- Institute of Laser Engineering, Osaka University, Suita 565-0871, Japan
| | - T Yabuuchi
- RIKEN SPring-8 Center, Hyogo 679-5198, Japan
| | - U Zastrau
- European XFEL, 22869, Schenefeld, Germany
| | - E Förster
- IOQ, Friedrich-Schiller University of Jena, 07743, Jena, Germany
- Helmholtz Institute at Jena, 07743, Jena, Germany
| | - F N Beg
- University of California San Diego, La Jolla, California 92093-0417, USA
| | - H Chen
- Lawrence Livermore National Laboratory, Livermore, California 94550-9234, USA
| | - A J Kemp
- Lawrence Livermore National Laboratory, Livermore, California 94550-9234, USA
| | - H S McLean
- Lawrence Livermore National Laboratory, Livermore, California 94550-9234, USA
| | - P K Patel
- Lawrence Livermore National Laboratory, Livermore, California 94550-9234, USA
| | - Y Ping
- Lawrence Livermore National Laboratory, Livermore, California 94550-9234, USA
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