Design Talbot Effect Long Focal Length Measuring System

Long-focus optical element and optical system are widely applied in various technical domains such as ICF,optical remote sensing, astronomical telescope and so on.Long focal length measurement based on Talbot-Moire effect is the hotspot of optical measurement.The principle of Talbot effect and moire fringe technology is studied,the long focal length measurement formula is deduced and a long focal length test device is established, it includes a collimated wavefront generator、a Talbot interferometer and a imaging system. The effect of wavefront aberration on accuracy of focal length is analyzed, the space between two gratings and angle of two grating lines as influencing factors on accuracy of focal length are analysed.Key components of the system are designed, a collimated wavefront generator is designed and its wavefront quality is better than λ/6,parameters of grating are designed,such as period,caliber and the angle of two grating lines;we process collimated lens,gratings and mechanical device. The alignment method to improve the accuracy is studied. Pentaprism method for the detection of wavefront is introduced to ensure that the collimated wavefront quality is better than λ/6;A reference reflective concave sphere is used for angle calibration,to make the accuracy of angle better than18".The long focal length measurement device is completed,then it is used to measure the focal length of lens which is about59.38m,the experimental results show that the repeatability and stability are better than0.03%,the reproducibility of device is better than0.8%.