The Laser Guide Star Facility (LGSF) is responsible for generating the artificial laser guide stars required by the TMT Laser Guide Star (LGS) AO systems. The LGSF uses multiple sodium lasers to generate and project several LGS asterisms from a laser launch telescope located behind the TMT secondary mirror. The LGSF includes 3 main subsystems: (1) the laser system, (2) the beam transfer optics (BTO) system, (3) the associated laser safety system. At present, the LGSF is in the preliminary design phase. During this phase, the laser launch telescope trade study, Beam transfer optical path trade study are compared carefully, and some critical components prototypes have been carried out to verify the requirements, such as the polarization status control and test, the Fast Steer Mirror (FSM) prototype test.
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.
An adaptive optics system (AOS), which consists of a 73-element piezoelectric deformable secondary mirror (DSM), a 9x9 Shack-Hartmann wavefront sensor and a real time controller has been integrated on the 1.8m telescope at the Gaomeigu site of Yunnan Astronomical Observatory, Chinese Academy of Sciences. Compared to the traditional AOS on Coude focus, the DSM AOS adopts much less reflections and consequently restrains the thermal noise and increases the energy transmitting to the system. Before the first on-sky test, this system has been demonstrated in the laboratory by compensating the simulated atmospheric turbulence generated by a rotating phase screen. A new multichannel-modulation calibration method which is used to measure the DSM based AOS interaction matrix is proposed. After integration on the 1.8m telescope, the closed-loop compensation of the atmospheric turbulence with the DSM based AOS is achieved, and the first light results from the on-sky experiment are reported.
A 3mm narrow interval deformable mirror (DM) with tip-tilt stage has been developed for astronomical instruments.
Benefiting from its compact design, the adaptive optics system can be built with simple structure and smaller optical
elements. First, a 37-elements prototype mirror has been developed for our 1.8-meter telescope, which interval space is
3mm, maximum tilt is ±10’, and maximum deformation is ±2μm. Based on this mirror, a simple adaptive optics system has been set up and its performance was tested in the laboratory especially the closed-loop correction ability. This
adaptive optics subsystem is scheduled to be mounted at one folded Cassegrain focus of the 1.8-meter telescope this
year, and comparison test for star compensation observation using this compact system and conventional adaptive optics
system will also be carried out at the same time.
In 2013, a serial sky test has been held on 1.8 meter telescope in Yunnan observation site after 2011-2012 Laser guide star photon return test. In this test, the long-pulsed sodium laser and the launch telescope have been upgraded, a smaller and brighter beacon has been observed. During the test, a sodium column density lidar and atmospheric coherence length measurement equipment were working at the same time. The coupling efficiency test result with the sky test layout, data processing, sodium beacon spot size analysis, sodium profile data will be presented in this paper.
We are developing a sodium guide star adaptive optics system for the 1.8 meter telescope, which consists of three
main parts: (i) 20W microsecond pulsed laser system, (ii) Φ200mm laser launch telescope and (iii) 37-elements adaptive
optics system. All of these three parts are mounted on the 1.8 meter telescope which is located in Gaomeigu site of
Yunnan Astronomical Observatory, Chinese Academy of Sciences. The pulsed laser system and the launch telescope are
rotated with the azimuthal base of the telescope. A miniaturized 37-elements low-order adaptive optics system including
a 37-elelment deformable mirror and a 6x6 array Hartmann-Shack wavefront sensor is mounted at the Cassegrain focus
taking account of the pulsed laser mode. A separate tip-tilt correction loop is also integrated into the system. This paper
describes the details of this system, the simulation result and the test result in the lab. After the indoor test, the whole
system will be shipped to 1.8 meter telescope. The latest commissioning status and results is presented also in this paper.
A method to retrieve small phase aberration from a single far-field image is proposed. It only needs to calibrate the
inherent aberration of the imaging system once, and then the difference between a single measured image with aberration
and the calibrated image with inherent aberration is got to retrieve the disturbed phase aberration by an approximate
linear relationship. Computer simulations are employed to analyze the performance of this linear phase retrieval (LPR)
wave-front sensor. The dynamic range of this method is discussed without noise to judge how small it is needed to
satisfy the method. The results show that the proposed small phase retrieval method works well when the RMS phase
error is less than 1.6 rad. The Linear Phase Retrieval wave-front sensor and the Hartmann-Shack wave-front sensor are
compared on the same stochastic wave-front aberration. The influence of different calculation condition on the retrieval
results is compared and analyzed. After analyzing the target resolution, it is thought that a reasonable target size is
advantageous to the retrieval precision. At the same time, the LPR sensor can realize the alike precision measurement by
using less detect cell, such as 8 pixelx8 pixel in our experiment. From the retrieval results of different orders, the error
rate are less than 0.25 and it is comparatively accurate to retrieve pre-35 order aberrations.
The basic principle of the linear phase retrieval (LPR) method is introduced. It is found that in small phase condition,
the odd and even parts of phase aberration can be obtained uniquely with a simple linear calculation method. The
difference between a single measured image with aberration and the calibrated image with inherent aberration are used
to retrieve aberration phases. In this paper, the principle of LPR and its application in close-loop AO system are
introduced in vector-matrix format, which is a kind of linear calculation and is suitable for real-time calculation.
Although the LPR method is limited for small aberrations only, it is suitable to use as a wavefront sensor in close-loop
adaptive optical system. The performances of the LPR method are tested in a close-loop adaptive optics system with
PZT deformable mirror. The experiment results show that the LPR method can be performed in real time and achieve
The basic principle and the characteristics of a new kind of linear phase retrieval (LPR) wave-front measuring method
were analyzed. It is proved that the unknown phase can be retrieved uniquely from only one far-field image with
calibration in advance. The principle construction of wave-front sensor developed from the LPR algorithm was
described. The performance of the LPR method was tested by numerical simulation on measuring the arbitrary disturbed
wave-front. The results showed that the LPR method was feasible on a certain system aberration condition, and it had
good ability on high-spacial resolution. In the lab, an experiment setup based on the LPR method had been built. The
experiment results testified the feasibility of this method and it could realize highly precision measure by using less
amount of detect elements.