INSTRUMENT DESCRIPTION AND PERFORMANCE EVALUATION OF A HIGH-ORDER ADAPTIVE OPTICS SYSTEM FOR THE 1 m NEW VACUUM SOLAR TELESCOPE AT FUXIAN SOLAR OBSERVATORY

Abstract

A high-order solar adaptive optics (AO) system including a fine tracking loop and a high-order wavefront correction loop has been installed at the 1 m New Vacuum Solar Telescope of the Fuxian Solar Observatory, in routine operation since 2016. The high-order wavefront correction loop consists of a deformable mirror with 151 actuators, a correlating Shack–Hartmann wavefront sensor with 102 subapertures of which the Absolute Difference Square Algorithm is used to extract the gradients, and a custom-built real-time controller based on a Field-Programmable Gate Array (FPGA) and multi-core Digital Signal Processor (DSP). The frame rate of the wavefront sensor is up to 3500 Hz and this is, to our knowledge, the fastest solar AO system. This AO system can work with a Fried parameter r 0, at the 500 nm wavelength, of larger than 3 cm. The first 65 modes of the Zernike aberrations can be efficiently corrected and the Strehl ratio of the corrected TiO image for the solar pore is superior to 0.75 with the Fried parameter r 0 larger than 10 cm. In this paper, the design of the system is described, and high-resolution solar observational images are presented. Furthermore, the performances of the AO system are evaluated according to the data recorded by the real-time controller.

Light Bridge and Magnetic Field in a Solar Active Region

“…Although there exist many observational data on the active region NOAA 12529 from space-and ground-based observations, we only employ observational data from the Helioseismic and Magnetic Imager (HMI; Scherrer et al 2012) working at the Fe I 6173 Å and the Atmospheric Imaging Assembly (AIA; Lemen et al 2012) working at seven EUV wavelengths (94, 131, 171, 193, 211, 304, and 335 Å) and two UV wavelengths (1600 and 1700 Å) on board the Solar Dynamics Observatory (SDO; Pesnell et al 2012) and high spatial resolution images from the multiwavelength simultaneous imaging system (MWSIS; Rao et al 2017), which is supported with the high-order solar adaptive optics technique (Rao et al 2016) and attached to the New Vacuum Solar Telescope (NVST; Liu et al 2014) located at Fuxian lake China.…”

Performance Characterization of Deep-Phase-Retrieval Shack-Hartmann Wavefront Sensors

“…Nevertheless, when the mode number continues to increase, the condition number of the reconstructed matrix would increase quickly. Thus the number of reconstructed mode coefficients in this approach is typically about 0.7 to 0.8 times the number of sub-apertures [10][11][12]. In addition, due to the similarity of the slope vectors, modal coupling and modal confusion errors are likely to occur, leading to a decrease in the accuracy of wavefront measurements [13].…”

Fabry–Pérot Interferometer-Based Tunable Narrow-Band Imager for Solar Chromospheric Observation: First Results

“…Today's advanced ground-based solar telescopes are regularly equipped with a FPIbased imaging spectrometer for tunable narrow-band imaging (Cavallini, 2006;Ravindra and Banyal, 2010;Puschmann et al, 2013). A benefit from the large aperture of the telescope (Rao et al, 2020), adaptive optics (AO) (Rao et al, 2016b(Rao et al, ,a, 2010, and postfacto imageprocessing techniques (Zhong, Tian, and Rao, 2014), is that more details of the features in the solar atmosphere can be studied.…”