关键词: 等离子体诊断/
空间分辨/
软X射线激光
English Abstract
Spatial resolution study of soft X-ray laser backlight shadow imaging technique
Wang Chen,An Hong-Hai,
Fang Zhi-Heng,
Xiong Jun,
Wang Wei,
Sun Jin-Ren
1.Shanghai Institute of Laser Plasma, Shanghai 201800, China
Fund Project:Project supported by the Science Challenge Project, China (Grant No. TZ2016005) and the National Natural Science Foundation of China (Grant Nos. 11075146, 61475146).Received Date:17 May 2017
Accepted Date:02 October 2017
Published Online:05 January 2018
Abstract:The soft X-ray laser shadow imaging technique is a good tool for diagnosing shadow profiles near the critical surface of high-temperature dense plasma. The short-pulse plasma X-ray laser, driven by high-power laser, is used as the backlight, which spreads freely approximately 500 mm far, passes through the plasma to be diagnosed, and changes its optical path by using a multi-layer spherical lens and multi-layer plane mirror, is attenuated by filters, and is recorded by a soft X-ray charge-coupled device (CCD). The plasma to be diagnosed can be driven by one or multiple laser beams, according to the needs of the physical research being conducted, and is imaged onto the CCD surface through a multilayer spherical lens. The shadow profile image of the plasma to be diagnosed at a particular time is obtained by using the instantaneous photographic mode of short-pulse soft X-ray laser backlight imaging. Compared with the traditional keV hard X-ray backlight technique, the soft X-ray laser shadow imaging technique has two distinct advantages. One is the appropriate wavelength of the probe light, which makes it possible to diagnose plasma near the critical surfac, and the other is a better spatial resolution because of the use of mature multilayer optical elements for near-normal incidence imaging. However, there has been no systematic study on the extent to which the spatial resolution of the imaging technology can be achieved. In this study, a careful analysis is carried out considering three aspects:the optical path geometry, the diffraction limit, and the imaging aberration. The results show that a spatial resolution of approximately 2 m can be achieved. An experiment is carried out to measure the Rayleigh-Taylor instability of plasma from the lateral direction, by using the soft X-ray laser shadow imaging technique. Some microfluids with a width of several microns can be clearly distinguished in the experimental shadow image, indicating that the diagnostic technique has a good spatial resolution. Further analysis reveals that the main factor that limits the spatial resolution is the optical path geometry. It is possible to achieve a spatial resolution of up to 1 m by increasing the magnification, selecting CCDs with smaller receiving units, etc.
Keywords: plasma diagnosis/
spatial resolution/
soft X-ray laser
