Pyramid wavefront sensor is a promising sensor technology based on the beam splitting in the focal plane. Due to its advantages of adjustable gain and variable spatial sampling, the pyramid wavefront sensor has been successfully applied in many large telescopes. In recent years, we have carried out the related research of this sensor. Firstly we studied the adaptive optical closed-loop system based on the liquid crystal spatial light modulator and the pyramid wavefront sensor. Subsequently, the adaptive optical system based on the pyramid wavefront sensor and the deformable mirror is studied in our lab. Currently the experiment on the 1.8-m telescope at Yunnan observatory has been successfully carried out and the high resolution images of the natural stellar star have been obtained. The experiment results are present in this paper.
During 2014-2016, the Laser guide star (LGS) adaptive optics (AO) system observation campaign has been carried out on Lijiang 1.8 meter telescope. During the campaign, two generation LGS AO systems have been developed and installed. In 2014, a long-pulsed solid Sodium prototype laser with 20W@400Hz, a beam transfer optical (BTO) system, and a laser launch telescope (LLT) with 300mm diameter were mounted onto the telescope and moved with telescope azimuth journal. At the same time, a 37-elements compact LGS AO system had been mounted on the Bent-Cassegrain focus and got its first light on observing HIP43963 (mV= 8.18mv) and reached Sr=0.27 in J Band after LGS AO compensation. In 2016, the solid Sodium laser has been upgrade to stable 32W@800Hz while D2a plus D2b repumping is used to increase the photon return, and a totally new LGS AO system with 164-elements Deformable Mirror, Linux Real Time Controller, inner closed loop Tip/tilt mirror, Multiple-PMT tracking detector is established and installed on the telescope. And the throughput for the BTO/LLT is improved nearly 20%. The campaign process, the performance of the two LGS AO systems especially the latter one, the characteristics of the BTO/LLT system and the result are present in this paper.
A composite tracking sensor, in which a reflect mirror with a central hole is inserted in the imaging systems so that the reflective beam beyond the hole is directed to the large dynamic range detector and the beam passing the hole is reimaged by a lens to enter the high sensitivity detector, can be used for tip-tilt detecting with high accuracy and large dynamic range simultaneously. A composite tracking sensor prototype based on the multi-anode photo-multiplier tubes (MAPMT) is developed for 1.8 meter astronomical telescope in the Gaomeigu astronomical observation station. In this paper, the principle of the composite tracking sensor is introduced. The prototype is described in detailed and the experimental results are presented. The results show that this composite tracking sensor can reach the tracking accuracy of 0.2 μrad and higher within the dynamic range of 870 μrad.
Proc. SPIE. 8418, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Smart Structures, Micro- and Nano-Optical Devices, and Systems
KEYWORDS: MATLAB, Digital signal processing, Coherence (optics), Error analysis, Adaptive optics, Field programmable gate arrays, Atmospheric turbulence, Atmospheric sciences, Atmospheric modeling, Atmospheric optics
To realize the measurement of atmospheric parameters, a kind of real time processor based on FPGA and DSP is proposed and designed. When Adaptive Optical (AO) system is close-loop, the FPGA reconstructs the open-loop Zernike coefficients from the close-loop data of residual slopes and corrected voltages, which are used for the later complex statistical calculations of the coherence length r0, the outer scale L0, the wind speed v and the coherence time t0 by the DSP. The errors of the open-loop Zernike coefficients reconstructed by FPGA are less than 3x10<sup>-8</sup> λ ( λ is the wavelength). The errors of the atmospheric parameters computed by DSP are less than 7.8x10<sup>-8</sup> cm (r0), 5.3x10<sup>−5</sup> m (L0), 7.5x10<sup>-7</sup> m/s (v) and 4.0x10<sup>-6</sup> ms (t0), respectively. For 127-element AO system at 1.8m telescope with 2000Hz sampling frequency, the processing latencies of FPGA and DSP are 19.65us and 553.8ms respectively, and the refresh time of atmospheric parameters is 1.85s. The results show that the proposed processor can be used to measure the real time atmospheric parameters.