Chunlin Guan

Performance of the 37-element solar adaptive optics for the 26 cm solar fine structure telescope at Yunnan Astronomical Observatory

A 37-element solar adaptive optics system, which consists of a fine tracking loop with a tip/tilt mirror and a correlation tracker, and a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann wavefront sensor, and a real-time controller, was built and installed at the 26 cm solar fine structure telescope of the Yunnan Astronomical Observatory in 2009. In this system, the absolute difference algorithm is used. A new architecture with field-programmable gate array (FPGA) and digital signal processor (DSP) for the real-time controller based on systolic array and pipeline was developed. The computational latencies of the fine tracking loop and high-order correction loop are about 35 and 100 mu s, respectively. The tracking residual root-mean-square error is less than 0.1 arcsec, and the wavefront residual root-mean-square error is about 0.05 wavelengths (lambda = 550 nm) after correction. The observational results show that the contrast and resolution of the solar images are improved after the correction by this adaptive optics system

37-element solar adaptive optics for 26-cm solar fine structure telescope at Yunnan Astronomical Observatory

A 37-element solar adaptive optics (AO) system was built and installed at the 26-cm solar fine structure telescope of Yunnan Astronomical Observatory. The AO system is composed of a fine tracking loop with a tip/tilt mirror and a correlation tracker, a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann wavefront sensor based on the absolute difference algorithm, and a real time controller. The system was completed on Sep. 28, 2009 and was used to obtain AO-corrected highresolution solar images. The contrast and resolution of the images are clearly improved after wavefront correction by AO. To the best of out knowledge, this system is the first solar AO system in China.

First light on the 127-element adaptive optical system for 1.8-m telescope

A 127-element adaptive optical system has been developed and integrated into a 1.8-m astronomical telescope in September 2009. In addition, the first light on a high-resolution imaging for stars has been achieved (September 23, 2009). In this letter, a 127-element adaptive optical system for 1.8-m telescope is described briefly. Moreover, star observation results in the first run are reported. Results show that the angular resolution of the system after adaptive optics correction can attain 0.1 arcsec, which approaches the diffraction limit of 1.8-m telescope at 700-900 nm band.

Decoupling algorithm of a double-layer bimorph deformable mirror: analysis and experimental test

With the increasing requirements on spatial resolution and actuator pitch, multilayer bimorph deformable mirrors are coming into wider application in adaptive optics. This paper discusses the coupling of actuators of multilayer bimorph deformable mirrors. A decoupling algorithm based on controlling gradients directly is presented. And a closed-loop adaptive optics system, which consists of a double-layer bimorph deformable mirror and a Shack-Hartmann wavefront sensor, is set up to validate this decoupling algorithm. Experimental results show that the intensity distribution at the image plane of the distorted wavefront is effectively improved when the modified closed-loop control is on. Besides, the experimental results fit well with the conclusion of numerical simulation.

Progress on the 127-element adaptive optical system for 1.8m telescope

The 127-element adaptive optical system for the 1.8m astronomical telescope is being developed. In this system, the wavefront correction loop consists of a 127-element deformable mirror, a Hartmann-Shack (H-S) wavefront sensor, and a high-speed digital wavefront processor. The tracking system consists of a tip-tilt mirror, a tracking sensor and a tracking processor. The wavelength for the H-S wavefront sensor ranges from 400-700nm. The imaging observation wavelengths range from 700-1000nm and 1000-1700nm respectively. In this paper, the optical configuration of 1.8m telescope will be briefly introduced. The 127-element adaptive optical system is described in detailed. Furthermore, the preliminary performances and test results on the 127-element adaptive optical system is reported.

An updated 37-element low-order solar adaptive optics system for 1-m new vacuum solar telescope at Full-Shine Lake Solar Observatory

A low-order solar adaptive optics (AO) system, which consists of a fine tracking loop with a tip/tilt mirror and a correlation tracker, and a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann wavefront sensor and a high-order wavefront correction controller, had been successfully developed and installed at 1-m New Vacuum Solar Telescope of Full-shine Lake (also called Fuxian Lake) Solar Observatory. This system is an update of the 37-element solar AO system designed for the 26-cm Solar Fine Structure Telescope at Yunnan Astronomical Observatory in 2009. The arrangement of subapertures of the Shack-Hartmann wavefront sensor was changed from square to hexagon to achieve better compensation performance. Moreover, the imaging channel of the updated system was designed to observe the Sun at 710nm and 1555nm simultaneously. The AO system was integrated into the solar telescope in 2011, and AO-corrected high resolution sunspots and granulation images were obtained. The observational results show that the contrast and resolution of the solar images are improved evidently after the correction by the AO system.

Performance on the 61-element upgraded adaptive optical system for 1.2-m telescope of the Yunnan Observatory

The 61-element upgraded adaptive optical system for the 1.2m telescope of Yannan Observatory for astronomical observation had been in operation since May 2004. In this paper, the 61-element upgraded adaptive optical system for 1.2m telescope of Yunnan Observatory will be briefly described. The performance on the 61-element upgraded adaptive optical system is analyzed. Furthermore, the observational results for the stars will be presented.

37-element adaptive optics experimental system and turbulence compensation experiments

A 37 element adaptive optics system has been built in the Institute of Optics and Electronics for experimental research of atmospheric effect compensation. In this system a 37 subaperture Shack-Hartmann sensor with frame rate 380 Hz is used as wavefront sensor, a 37/55 element deformable mirror and a fast steering mirror as wavefront correctors, a digital signal processor with peak operation speed 100 Mops as wavefront processor and controller, and 39 channels of high voltage amplifier for controlling the wavefront correctors. This system has been integrated with a turbulence cell developed by the Anhui Institute of Optics and Fine Mechanics and experiments for compensating for wavefront errors induced by the turbulence of the cell with different strength have been conducted. Another Shack- Hartmann wavefront sensor is used for measuring the strength of turbulence. The integrated probability density functions of both the coherence length r0 and the Strehl ratio of S of the focused spot are used to describe the strength of turbulence and the sharpness of focused spots with and without correction. In this paper the adaptive optics system and the experimental results are briefly reported.

Hysteresis compensation of piezoelectric actuator for open-loop control

Received January 21, 2013; accepted March 5, 2013; posted online July 30, 2013 The hysteresis nonlinearity of piezoelectric actuator is one of the main defects in the control of deformable mirror which is widely used as a key component in adaptive optics system. This letter put forward a modified Prandtl-Ishlinskii (PI) model in order to precisely describe the hysteresis nonlinearity of piezoelectric actuator. With this proposed model, an inverse-model based controller used for trajectory tracking in open-loop operation is designed to compensate the hysteresis nonlinearity effect. Then, some tracking control experiments for the desired triangle trajectory are performed. From the experimental results, we can see that the positioning precision in open loop operation is significantly improved with this inverse-model based controller.

Adaptive optical system based on deformable secondary mirror on 1.8-meter telescope

In 2009, A 127-element adaptive system had been manufactured and installed at the Coude room of the 1.8-meter telescope at the Gaomeigu site of Yunnan Astronomical Observatory, Chinese Academy of Sciences. A set of new adaptive optical system based on a 73-element deformable secondary mirror is being developed and will be integrated into the 1.8-meter telescope. The 73-element deformable secondary mirror with convex reflecting surface is designed to be compatible with the Cassegrain focus of the 1.8-meter telescope. Comparing with the AO system of Coude focus, the AO system on the deformable secondary mirror adopts much less reflections and consequently restrains the thermal noise and increases the energy transmitting to the system. The design and simulation results of this system will be described in this paper. Furthermore, the preliminary test result of the deformable secondary mirror in the lab is also presented.