Optimizing the location of multiple laser guide stars in ground layer adaptive optical systems

Li Caifeng; Jia Peng; Cai Dongmei

doi:10.12086/oee.2020.190515

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Li C F, Jia P, Cai D M. Optimizing the location of multiple laser guide stars in ground layer adaptive optical systems[J]. Opto-Electron Eng, 2020, 47(9): 190515. doi: 10.12086/oee.2020.190515

Citation:

Li C F, Jia P, Cai D M. Optimizing the location of multiple laser guide stars in ground layer adaptive optical systems[J]. Opto-Electron Eng, 2020, 47(9): 190515. doi: 10.12086/oee.2020.190515

Optimizing the location of multiple laser guide stars in ground layer adaptive optical systems

1.
Institute of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China
2.
Key Laboratory of Advanced Transducers and Intelligent Control Systems, Ministry of Education and Shanxi Province, Taiyuan, Shanxi 030024, China
3.
Center for Advanced Instrumentation, Durham University, Durham DH1 3LE, UK

Fund Project: Supported by National Natural Science Foundation of China (11503018, U1631133), Shanxi Province Science Foundation for Youths (201901D211081), Research and Development Program of Shanxi (201903D121161), the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (2019L0225)

More Information

^*Corresponding author: Jia Peng, E-mail: robinmartin20@gmail.com

Received Date 02 September 2019

Revised Date 02 December 2019

Published Date 15 September 2020

Abstract

Abstract

At present, the ground layer adaptive optical systems are using multiple laser guide stars arranged in regular polygons as reference targets to measure the effects of atmospheric turbulence. Obtaining the optimal position of laser guide stars becomes an interesting problem to analyze. This paper proposes a method to obtain the optimal position of laser guide stars by using a genetic algorithm as the optimization algorithm and a simplified geometry model of the ground layer adaptive optic system as the evaluation function. Furthermore, multi-process, Numba library, and multi-thread techniques methods are used to accelerate calculation speed. Based on these methods, real atmospheric turbulence profiles are used to analyze the relationship between the optimal position of laser guide stars with different numbers and the different atmospheric turbulence profiles from the same site, through an example of a ground layer adaptive optics system with 14 arcmin field of view. The results show that the optimal position of laser guide stars in the same site is almost the same and their statistically optimal positions are all regular polygon. Besides, we also find that the spatial resolution of turbulence profiles has strong effects to positions of laser guide stars, showing that the more equivalent layers in the measurement results, the closer the position distribution of laser guide stars is to the regular polygon.
- laser guiding stars /
- atmospheric turbulence /
- genetic algorithm /
- location optimization /
- algorithm to accelerate

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References

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Overview

Overview

Overview: The ground layer adaptive optic system (GLAO) uses wavefront sensors to measure wavefront errors from several different field of views and corrects the 'mean' wavefront errors from these measurements with a deformable mirror, which could slightly increase image quality in a wide field of view. The GLAO is particular useful for multi object observations, such as multi-object spectroscopic observations and wide field astrometry or photometry. The GLAO system normally assumes that there is a ground layer atmosphere turbulence in a fixed height, and thus it uses several laser-guide stars with fixed positions in the field of view to measure wavefront errors from that layer. However, the atmospheric turbulence is a stochastic medium and the height and strength of the ground layer will change continuously in real applications. Does there still exist optimal positions for these laser guide stars? Calculating the performance of the GLAO system with different configurations under different turbulence profiles is a straight forward method to obtain the optimal position of laser guide stars, but it will cost a very long time. In this paper, a simplified geometric model is proposed to evaluate the performance of the GLAO system. The genetic algorithm is used to obtain optimal positions of laser guide stars for different turbulence profiles from real measurements of different sites. Because there is a huge amount of atmospheric turbulence profiles, multi-processing, Numba library, and multi-thread techniques are used to further accelerate the computation speed up 3240 times that of the ordinary method. Based on the aforementioned methods, we have evaluated the GLAO performance with laser guide stars of different locations under different turbulence profiles from Paranal and Mauna Kea. We assume the turbulence profiles as random variables of independent and identically distributed and random sample a small batch (2000 turbulence profiles from different sites) to estimate the optimal position of laser guide stars. We have found that the optimal position of laser guide stars in the same site is almost the same and their statistically optimal positions are all regular polygon. However, we have also found that the spatial resolution of atmospheric turbulence profile measurements has strong impacts to the performance evaluation, showing that higher spatial resolution can lead to a more concentrated distribution of the laser guide stars. It indicates that it is necessary to obtain enough high-resolution turbulence profile data to better evaluate site conditions for China future large telescopes with GLAO systems.