Research On Active Optical Correction And Wavefront Compensation Methods For Off-Axis Reflective Systems

In recent years,the high-resolution space reflective systems are widely used in many fields such as science,military and social life.One of the main development trends of this kind of system is lightweight and large aperture.It is easily affected by severe environments such as vibration and thermal stress,which will cause system aberrations and degrade the imaging capabilities.With the increase of the aperture size and the performance requirements,it is necessary for space-based optical systems to be equipped with active optical adjustment mechanisms to correct or compensate the system perturbations.The active optical correction and compensation methods are the suitable ways of correcting or compensating the perturbed systems.It is of great significance to the implementation of active optical systems.Specifically,active correction refers to the complete correction of misalignments and surface figure errors to restore systems to the nominal state;active compensation refers to compensate the system wavefront error based on limited active adjustment devices to meet the performance requirements.The calculation of correction and compensation values is the key work.Compared with the traditional coaxial reflective systems,the off-axis reflective systems have the advantages of large field-of-view,high optical throughput and high signal-to-noise ratio,which are more and more used in practical engineering.However,the rotational symmetry of off-axis systems is broken,so the related theories and methods are difficult.At present,the active optical correction and compensation methods for the off-axis systems are still immature and need to be further studied.It has important theoretical and practical significance for the development of active optical technology of off-axis reflective systems.In the framework of nodal aberration theory,the active optical correction and wavefront compensation methods of off-axis reflective systems are studied in this dissertation.Firstly,the correction method of off-axis reflective systems with complex surface figure errors is discussed.Then,the correction method of perturbed off-axis reflective systems using the extension of nodal aberration theory is studied.Finally,the active compensation for optimal RMS wavefront error in perturbed off-axis reflective systems is studied.Specifically,the main contents of this dissertation are as follows:The method of calculating correction values for the off-axis reflective systems with complex surface figure errors(located at the stop and away from the stop)is presented.Based on Zernike polynomials,an analytical description of the wavefront aberration contribution of the freeform surface to the off-axis system is derived.And then,based on the analytical description,a correction model of the off-axis systems with complex surface figure errors(located at the stop and away from the stop)is established.Finally,the off-axis two-mirror system is taken as an example,and the proposed method is verified and analyzed.The results show that the high accuracy of the proposed method.The correction method of complex perturbed off-axis reflective systems using the extension of nodal aberration theory is proposed.For some complex cases,the low-order aberrations are not enough to represent the system performance,so it is necessary to consider the extension of nodal aberration theory.Firstly,the direct expansion of the wave aberration function in the vector form for perturbed off-axis systems is given.Then,the inherent vector relationships between the contributions generated by the aberrations of the on-axis parent systems through pupil transformation are revealed.And then,the correction model based on NAT for complex cases of perturbed off-axis systems is established.The correction model is solved by using particle swarm optimization algorithm.Finally,an optical correction example of the complex off-axis three-mirror system based on the proposed method is given.The results demonstrate the correctness and accuracy of the proposed method.Aiming at the problem of wavefront compensation based on the principle of minimum engineering cost,the active compensation strategy for RMS wavefront error in perturbed off-axis optical systems using nodal aberration theory is presented.In practical engineering,in order to reduce the system complexity,it is of great significance to use limited adjustment devices to compensate the performance of space-based optical systems.Firstly,the orthogonalized expression of wave aberration function in the vector form for perturbed off-axis systems is derived by using RMS normalization.Then,the system compensation model for perturbed off-axis systems is established.Finally,the off-axis three-mirror anastigmatic system is taken as an example,and the system compensation for the misaligned tertiary mirror and the deformed primary mirror is discussed.After compensation,the average RMS wavefront errors in the perturbed off-axis systems are greatly reduced,which can well meet the system requirements.An off-axis three-mirror system with a 6m focal length is used as the experimental platform to verify the proposed compensation method.Specifically,the system wavefront is compensated by the misalignments of the secondary mirror,which is often used in practical engineering.The corresponding experimental results are discussed,which show the effectiveness of the proposed compensation method.