Study On The Adaptive Optics Pyramid Wavefront Sensing Method

The adaptive optics is proposed by Badcock in 1953,and the concept is that the wavefront aberration can be reduced by real time compensation,so as to improve the image quality of the system.After 60 years,adaptive optics technology has been widely used in various modern optical systems,for example the high resolution imaging telescope,laser fusion system,retinal imaging system,free space optical commutication system and so on.As the feedback element for real-time detection,wavefront sensor is an important part of adaptive optics system.There are some common wavefront sensors,such as Shack-Hartmann wavefront sensor,shearing interferometer,curvature wavefront sensor,pyramid wavefront sensor,and holographic wavefront sensor.In 1996,Ragazzoni proposed the pyramid wavefront sensor,which is similar as Foucault knife edge test.Compared with other common wavefront sensors,pyramid has some advantages,like high sensitivity,high light energy utilization,adjustable sampling rate,and suitable for the weak light detection.Now,pyramid wavefront sensor has been applied in many large telescopes.In this paper,the theoretical analysis and the numerical simulation of three common pyramid wavefront sensors,namely two-sided pyramid,three-sided pyramid,and four-sided pyramid,are studied.We introduce the four-sided sequential pyramid wavefront sensor,and analysis the chracteristics compared with the four-sided pyramid.Based on the above work,we propose the three-sided sequential pyramid wavefront sensor based on a micromirror array with hexagonal geometry.We discuss the selection of parameter index that is used in our experiment and build a closed-loop system with this wavefront sensor and a 21-element deformable mirror as a wavefront corrector.The main contents of this paper are as follows:1.The common traditional refractive pyramid wavefront sensing methods are described.We simulate the adaptive optics systems with two-sided pyramid,three-sided pyramid,and four-sided pyramid,compare the results of the light energy utilization,wavefront reconstruction accuracy,and the residual wavefront of closed loop iterations.2.The four-sided sequential pyramid wavefront sensor is introduced.We simulate the detection images from Fourier optics theory,compare the light energy utilization of the sequential pyramid and traditional pyramid,and use the four-sided sequential pyramid to correct the static atmospheric turbulence screen in numerical simulation.3.The three-sided sequential pyramid wavefront sensor is proposed.We use a micromirror array with hexagonal geometry to instead of the refractive pyramid prism.The geometrical optics analysis and numerical simulations show that a linear relationship exists between the signals calculated by the sensing data and the local tilt of the wavefront.The numerical simulations compare the enery utilization of the three-sided and four-sided sequential pyramid.4.The adaptive optics system based on three-sided sequential pyramid wavefront sensor is built.The micromirror array with hexagonal geometry is introduced.The gradient wavefront reconstruction based on sequential pyramid is proposed.The experimental results confirm the feasibility of using a three-sided sequential pyramid wavefront sensor in adaptive optics systems.