Gaussian beam modes analysis for uncertain off-axis mirror's parameters

In quasi-optical system, the co-polarization and cross-polarization caused by off-axis mirrors should be paid attention to seriously, When we design a reflector system we need to know the parameters of a mirror (like focal length, position or others) in advance so that we can formulate the input and output fields even the data we need by the known parameters of system. In this paper, we will improve an existing Gaussian beam mode analysis (GBMA) to apply in the opposite case, which we don't know the parameters of a mirror. By using its computing method, we can also get the optimal value of the parameters about the uncertain mirror in the system with cross-polarization and co-polarization the first mirror generated. In order to verify the accuracy of this method, we will compare the cross-pol isolation in GBMA and the physical optics (PO) in commercial software GRASP10 with the results' value and the results' curve change.