Investigation Into Design And Application Of The X-ray Shifted Dual Transmission Grating Spectrometer

In the diagnostics of inertial confinement fusion,precise measurement of the soft X-ray spectra is crucial to help understand mechanism of the laser-plasma interactions and plasma conditions. Transmission grating spectrometer(TGS) has been extensively used to measure soft X-ray spectra in laser produced plasma experiments, which shows a good spectral resolution, a wide photon energy range and simple operation.By the limited length of the recorder, the measured spectral range and resolution are restricted with each other when use the TGS to measure the X-ray spectra. Generally, the length of the spectrometer is fixed, low line density grating has an adequate spectral resolution in low photon energy range, but poor in high photon energy stage. The spectral resolution can be further enhanced when using high line density grating, but the measured spectral range is reduced as limited by the length of photocathode in X-ray streak camera.Therefore, a novel shifted dual transmission grating spectrometer(SDTGS) is herein conceived to solve this problem. The SDTG can measure a wide photon energy range of soft X-ray spectrum with high resolution. Coupling the SDTG with a streak camera, a 0.1~5keV time-resolved spectra can be obtained.Our SDTG composes of two sub transmission gratings, 2000 lines/mm and 5000 lines/mm, respectively, by which the axes are shifted horizontally and vertically with a certain distance. According to the theoretical analysis, one sub grating(2000 lines/mm) is designed to measure the soft X-ray spectrum ranging from 0.1 to 1.09 keV and the spectral resolution is 0.11 nm, the other(5000 lines/mm) is responsible for the ranges of 1.09 to 5keV and the spectral resolution is 0.05 nm.Two sections of X-ray spectrum are projected onto the cathode slit of streak camera and broad band time-resolved spectra are recorded.In order to get these gratings’ absolutely diffraction efficiency, both of them have to been calibrated using monochromatic light. Thus, the new dual grating component was calibrated within the energy range from 200 to 1600 e V on Beijing Synchrotron Radiation Facility. From this calibration experiment, the diffraction characteristics were obtained. The efficiency theoretical value was eventually obtained under different parameters with the rigorous coupled-wave analysis.In addition, the imaging properties of the SDTG were characterized in the X-ray region in detail by calibration. The results were consistent with our anticipation. Furthermore, a detailed experiment will be scheduled to test and verify the feasibility of SDTG spectrometer. Eventually, this SDTG may become a promising device, which will be expected to be used for an excellent quality, high resolution, and broad X-ray spectral ranges in the diagnostics of inertial confinement fusion.