Control Method And Application Research For Piezoelectric Deformable Mirror

Adaptive optics technology measures the wavefront distortion in real-time, and corrects the wavefront distortion based on the phase conjugate principle to improve the optical system resolution. Adaptive optics was first proposed and applied in astronomy telescopes to compensate the effect from some dynamic disturbances, such as the atmosphere turbulence. After several decades of development, adaptive optics technology has been widely used in many areas, such as astronomical telescopes, retinal imaging, laser fusion systems, laser fabrication, bio-microscopy and laser communications, and so on. As a frequently-used wavefront corrector, piezoelectric deformable mirror is attractive for its large stroke and high bandwidth. In this dissertation, the control method and application of the piezoelectric deformable mirror are selected as the main research content. The main research work are introduced as follows.(1) An unimorph piezoelectric deformable mirror with214actuators was developed for telescope applications, and this deformable mirror has the following advantages, such as excellent aberration correction performance, lightweight, low driving voltage, low power consumption and high process stability. The mechanical model of this deformable mirror is built, and the structural parameters were determined based on the model. Then the key performance parameters, such as stroke, and aberration correction ability, were simulated through numerical simulation. In fabrication of this deformable mirror, fabrication flow and key technology, electrical connection and packaging technology were studied. After the prototype for this deformable mirror is developed, the key parameters, such as initial surface of the deformable mirror, actuator stroke, response frequency, and the ability for correction initial aberrations of the deformable mirror and reconstruction for Zernike aberrations were tested and characterized. Through "ground" electrode bias and double drive modes two kinds of methods, this deformable mirror achieved bi-directional deformation driven by only positive voltage. The results of these theoretical analysis, simulations and tests prove that this deformable mirror has the potential to be used in astronomical applications.(2) The control methods for the adaptive optics system based on direct wavefront measurement were studied. An adaptive optics experimental system based on direct wavefront measurement was built using a home-made piezoelectric unimorph deformable mirror. The steepest descent method and iterative learning control method were used to control the piezoelectric unimorph deformable mirror in experiments of system aberration correction and specific Zernike aberration reconstruction. Besides, the aberration correction ability of the214-actuator unimorph piezoelectric deformable mirror was tested in the experimental system.(3) In wavefront sensor-less adaptive system, there are several frequently-used control methods. While hill-climbing algorithm suffers from the local optimum problem, and the global optimum algorithms, such as genetic algorithm, simulated annealing algorithm, stochastic parallel gradient descent algorithm, have low correction efficiency. To solve this problem, hybrid simulated annealing-hill climbing algorithm is proposed, which can guarantee correction effect and improve correction efficiency. To improve correction efficiency furthermore, hill-climbing algorithm based on Zernike modes was proposed. The mathematical model for this algorithm was established, and this algorithm is proved to be not affected by the local optimum problem from the mathematical model. Numerical simulations and spot correction experiments were conducted, and the results indicated this algorithm can find the global optimal value with high efficiency. Besides, the robustness of this control algorithm for mismatched center position and aperture were studied by simulations and experiments.(4) For femtosecond laser processing spot suffers from aberrations, an adaptive optics system is introduced into femtosecond laser processing system. The mathematical model for refractive index mismatch aberration is established, and the effect to processing spot intensity in different conditions of processing depth, refractive index mismatch degree, numerical aperture of the objective lens were calculated. A femtosecond laser processing system with an adaptive optics system was built. In experiments, system aberrations and refractive index mismatch aberrations are corrected separately. After correction, the peak intensity of focal spot is improved.There are some creative points in this dissertation as follows:1. Two new algorithms, hybrid simulated annealing-hill climbing algorithm and hill-climbing algorithm based on Zernike modes are proposed to improve the correction effect and correction efficiency.2. For applications in telescopes, an unimorph piezoelectric deformable mirror with214actuators is proposed, and the design, fabrication, package and test of this deformable mirror are achieved.3. An adaptive optics system is introduce into femtosecond laser processing system to correct aberrations, and the peak intensity of focal spot is improved after correction.