Design Of Focal Length Measurement System Based On Double Grating Interference Technology And Its Key Technology Research

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 Double-grating interferometry is the hotspot of optical measurement.The principle of double-grating interferometry 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 double-grating interferometer and a imaging system.The focal length measuring range is from 5m to 80m,and the caliber of the system is 100mm.The effect of wavefront aberration on accuracy of focal length is reduced,the measuring range,sensitivity,relative error and the angle of two grating lines as influencing factors on accuracy of focal length are analysed.Key components of the system are designed and established.According to the difficulty of long-range and long focal length measurement,A non-focal length calibration method base on focal length measurement function which uses collimated beam,lenses of focal length of 5m and 59m combined to calibrate the error of parameter of the system.The method improved the accuracy of focal length measurement among the range of 5m to 80m.The long focal length measurement device is completed,then it is used to measure the lenses whose focal length is about 4.95m,38.06m and 59.42m under the certain angle of grating lines,the experimental results show that the average relative errors are 0.10%,0.13%and 0.52%,the repeatability is better than 0.021%.