| Adaptive optics (AO) technology has the ability to overcome the influence of the dynamic aberrations caused by dynamic disturbance such as atmosphere turbulence.The astronomical observation can achieve the diffraction limit resolution of the imaging system by measuring and correcting the atmospheric induced wavefront distortion in real-time. Deformable mirror (DM) is one of the most common wavefront corrector in AO system, whose performance determines the correction performance of the AO system. The requirement of correction performance of the DM increases rapidly with the increase of the aperture of primary mirror, which will be larger than 30 meters in the next generation of terrestrial telescopes. The next generation of telescopes and the currently operating telescopes demand of thousands of actuators (related to the aperture of telescope) and hundreds of operating bandwidth (related to the wavelength of observation). Piezoelectric DM has the advantages of large deformation, low driven voltage, low-cost and lightweight. Nevertheless, the operating bandwidth of the piezoelectric DM is in inverse proportion to the aperture of telescope. It is difficult to fabricate piezoelectric DM with the advantages of large aperture and high bandwidth in the same time, limiting its application in astronomy. In this dissertation, we devote ourselves to developing piezoelectric DMs with large aperture, high bandwidth and high spatial frequency, based on the performance requirement of the DM in the application of astronomical observation. The research contents are as follows:(1) The impact analysis of atmospheric aberration and the simulation to generate atmospheric aberration. The impact of the atmospheric aberration on astronomical imaging is analyzed theoretically. Based on the theoretical results, the requirements of actuator number, stroke, and temporal bandwidth of the DM are analyzed. The simulative random turbulence screen is generated successfully, based on the average atmospheric environment parameters of the Very Large Telescope (VLT). The impact analysis of atmospheric aberration and the simulation to generate turbulence screen lay a good foundation for the design, fabrication and verification of the correction performance of DMs for astronomical applications.(2) Research on a woofer-tweeter DM with large aperture and high bandwidth. Based on the requirement of DM for turbulence aberration correction of telescope of 10 meters in diameter, the problem of the degradation of the bandwidth with the increase the aperture of the conventional piezoelectric DM is analyzed.To overcome this problem,a woofer-tweeter DM working with a unimorph DM layer and a drive array layer is proposed. A prototype is fabricated successfully after the research of key technologies of the fabrication processes of the woofer-tweeter DM. The aperture is 80 mm in diameter. The first resonance frequency is about 950 Hz. The PV value of the DM profile is less than 10 m. After correction, the RMS error of the DM profile is less than 15 nm. Affter the correction of random turbulence aberration generated by simulation, the RMS residual error is about 38.6 nm (<?/50, ?=2.2 m), indicating that the woofer-tweeter DM can correct the turbulence aberration of telescope of 10 meters in diameter.(3) Research on the characterization method of the DM performance. A large aperture DM test system is built using a Shack-Hartman wavefront sensor. The optical configration is optimized to reduce the optical aberration of system. The DM test system can evaluate the performance such as stroke, influence function, coupling, the reconstruction capability of Zernike aberrations and the closed loop correction capability of DMs with aperture less than 80 mm.(4) Research on intracavity AO correction. In order to achieve maximum output power in different pump power, an intracavity AO system is built to compensate the influence of thermal effect. After correction, the Nd:YAG rod laser works steadily,while the output power degrades severely before correction due to the thermal effect.The maximum increase rate of output power before and after correction is 43.6%.Moreover, the output power of the Nd:YAG rod laser is further increased thanks to the intracavity AO system.The creative point in this dissertation is that a woofer-tweeter DM with large aperture and high bandwidth is proposed, the prototype is fabricated successfully and its performance is evaluated. The woofer-tweeter DM overcomes the degradation of the bandwidth with the increase of aperture of the piezoelectric DM, having the advantage of high bandwidth and high special frequency. The woofer-tweeter DM is scalable,whose aperture (actuator number) can be scaled up while maintaining high bandwidth,making the piezoelectric DM fits the demand of application of larger telescopes. |
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