The New Vacuum Solar Telescope (NVST) is a 1 meter vacuum solar telescope that aims to observe the fine structures on the Sun. The main tasks of NVST are high resolution imaging and spectral observations, including the measurements of solar magnetic field.NVST is the primary ground-based facility of Chinese solar community in this solar cycle. It is located by the Fuxian Lake of southwest China, where the seeing is good enough to perform high resolution observations. In this paper, we first introduce the general conditions of Fuxian Solar Observatory and the primary science cases of NVST. Then, the basic structures of this telescope and instruments are described in detail. Finally, some typical high resolution data of solar photosphere and chromosphere are also shown.
Atmospheric turbulence severely limits the performance of ground-based imaging and laser propagation systems. Some observational results, showing atmospheric turbulence which does not obey Kolmogorov's theory, have prompted the study of optical propagation through non-Kolmogorov turbulence. This paper presents a theoretical approach to analyse the spatial and temporal characterizations of phase fluctuations in non-Kolmogorov turbulence. The spatial structure function, the temporal structure function and the temporal power spectrum of phase fluctuations are derived. The generalized coherence length PO, the characteristic frequency fR and the characteristic time TR are expressed as functions of the index structure constant along the propagation path and the wind velocity. The long exposure MTF, the short exposure MTF and the imaging Strehl ratio are computed.
Wavefront sensorless adaptive optics (AO) systems have been widely studied in recent years. To reach optimum results, such systems require an efficient correction method. In this paper, a general model-based correction method for a wavefront sensorless AO system is presented. The general model-based approach is set up based on a relationship wherein the second moments (SM) of the wavefront gradients are approximately proportionate to the FWHM of the far-field intensity distribution. The general model-based method is capable of taking various common sets of functions as predetermined bias functions and correcting the aberrations by using fewer photodetector measurements. Numerical simulations of AO corrections of various random aberrations are performed. The results show that the Strehl ratio is improved from 0.07 to about 0.90, with only N + 1 photodetector measurement for the AO correction system using N aberration modes as the predetermined bias functions.
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