Research On Alignment Technology For Off-axis Parabolic Collimator Based On Reverse Hartmann

The off-axis parabolic collimator,which is used to provide parallel light for the detection of the optical system,has the advantages of simple structure,no chromatic aberration and no obstruction at the center.Especially,with the increasing higher demand on the optical system diameter,and the further research on the off-axis optical system,more and more researches have been done on the off-axis parabolic mirror collimator.The accuracy of the alignment will directly affect the quality of the collimated light.The main installation method now is the auto-collimated interference method.Auto-collimated interference is highly accurate,but it requires a plane mirror as reference.And large-diameter plane mirror is very difficult to process,and easily transformed due to gravity,temperature,vibration,and airflow.In this paper,an off-axis parabolic mirror collimator alignment method based on the inverse Hartmann method is proposed,which is suitable for adjusting the position of the point light source,after the rough alignment of the off-axis parabolic mirror collimator.The Zernike polynomial coefficients are obtained by using the inverse Hartmann method.Through simulation,the relationship between the Zernike coefficient and the amount of collimator misalignment is obtained.According to the relation,the misalignment of the point light source could be calculated to guide the installation.In this paper,the principle and implementation process of the inverse Hartmann method are introduced in detail.An off-axis parabolic collimator model is established.Based on the model,the relationship between the Zernike coefficient and the offset is able to be calculated.Then according to the requirements of wave aberration,the demand for the accuracy of the point light source alignment is raised.The influence of the position error of the graphic generator and the camera on the alignment is analyzed in this paper The allowable range of the error and the method of reducing the error are given.According to the optimal pinhole size and proper projected pattern calculated,the fixing and adjusting structures of the system components are designed.Based on the key components selected,the reverse Hartmann method is designed and built.In a word,this method is applied for the alignment of an existing off-axis parabolic collimator,which interferometer could test the result of the wave aberration.