Performance Analysis Of High Spectral Resolution Solar Grating Spetrometer And Experiment Validation

It is well known that the evolving magnetic field causes the solar atmosphere eruption, and it produces most of the sometimes spectacular visible phenomena, such as the sunspots, prominences, flares, coronal mass ejections and so on. Real time observation and forecast of the solar atmosphere activities are very important since the violent activities of the solar atmosphere and period variation will influence the living environment of human being, and the imaging solar grating spectrometer is an important tool to obtain this goal. It not only can perform the imaging observation, but also can perform the spectral observation and identify the thermodynamics parameters of the solar atmosphere by the spectral information, such as the magnetic field, pressure and element abundance. As a result, the imaging grating spectrometer is broadly applied in the solar atmosphere observation.The high spectral resolution solar grating spectrometer is studied in this paper, including the optical design on the high spectral resolution solar grating spectrometer, protype construction, the analysis of the influence of the wavefront aberration on the imaging performance of the solar grating spectrometer and the experiment validation.Firstly, a high spectral resolution solar grating spectrometer based on the New Vacuum Solar Telescope(NVST) is designed, and it can operate at 656.3nm and 854.2nm, simultaneously. To attain the excellent imaging performance of the solar grating spectrometer, the wavefront aberration, such as spherical aberration, coma aberration and astigmatism aberration, are compensated. The parameters of the solar grating spectrometer are determined and are optimized by the software of the ZEMAX. The result shows that diffraction-limited imaging performance of the solar grating spectrometer is attained.Secondly, the prototype of the high spectral resolution of the solar grating spectrometer is constructed, and the constructed process is systemically introduced, including instrument design, key element design, white light spectral profile measurement and wavelength calibration, and the real spectral resolution measurement. To well compensate the wavefront aberration of the prototype, the AO system is integrated in the system. The prototype can operate in the wavelength range between the 0.6μm and 1.1μm. The real spectral resolution is 5.6pm@632.8nm, reaching the same spectral resolution among the similar instruments in the world. Besides, the real spatial resolution is 55μm, which is very close to the diffraction-limited imaging performance of the solar grating spectrometer(50μm).Thirdly, unlike the general optical system, the slit of the grating spectrometer is tiny enough, and it will filter the wavefront aberration to some certain extent. The mathmatical relation between the wavefront aberration and the imaging performance of the solar grating spectrometer is derived, and the numerical simulation is carried out. The numerical simulation results show that: the influence of the different types and diffenernt magnitudes Zernike aberration on the imaging performanence of the solar grating spectrometer is different after the filter slit, compared with the influence before the filter slit, the influence is smaller. The smaller the slit is, the smaller the influence is. However, that is not true for the low-fruquency dominated aberration, such as the defocus, since most of the low-frequency of the aberration will be blocked by using a smaller filter slit. If the influence of the filter slit on the wavefront aberration can not be taken to account, it will lead to AO over compensation.Finally, to quantitatively study the influence of the wavefront aberration and the influence of the AO on the imaging performance of the solar grating spectrometer, the AO system based on the Hartmann Shack Wavefront sensor(HS WFS) and the electrically addressed phase-only liquid-crystal spatial light modulator(LC-SLM) is integrated in the solar grating spectrometer to perform the closed-loop correction experiment. The experiment results show that the influence of the wavefront aberration on the spectral resolution can be ignored and the energy utilization η is considerably improved, better than 95%.The high spectral resolution solar grating spectrometer with high energy utilization is important to the high accuracy imaging observation and high spectral resolution spectral observation of the solar atmosphere.