The Development And Analysis On Measurement System For Diffraction Efficiency Of Convex Gratings

Convex grating imaging spectrometers which can offer fast aperture,high spectral resolution and compact structure have received a great deal of attention both in China and abroad,because of the development in fabrication techniques for convex gratings.They have been applied as remote sensing instruments in the areas of mineral exploration,agriculture,forestry,environment hazards assessment,urban study and so on.The convex grating is the core part of the convex grating imaging spectrometer,and its diffraction efficiency not only has a direct impact on the imaging spectrometer’s energy transmission properties,but can also provide useful references for the grating fabrication process.So it’s significant to develop a measurement system for diffraction efficiency of convex gratings and analysis its measuring performance.Firstly,the history,basic features of gratings and the current research situations of the measurement systems for diffraction efficiency are introduced.Three different measuring methods are summed up.They are multiple-line method,continuous scanning method and Fourier transform method,and their measuring principles,advantages and disadvantages are analyzed.The multiple-line method is chosen as the measuring method,after the diffraction characteristics of the convex grating are revealed.Then,the structure of the measurement system which includes four main components as light source,front system,dispersing system and detector is analyzed.Next,the optical scheme for this measurement system is designed.With the help of Zemax optical design software,the spot diagram on the image surface and the results of real ray trace are given.At last,based on Solidworks physical model design software,a simulation model of the measurement system is constructed.In order to verify the correctness of the designed measurement system,the measurement system is set up and the diffraction efficiency of a convex grating with the aperture of 35 mm,the curvature-radius of 72 mm,the blazed angle of 6.4°,the grating period of 2.5μm and the working waveband of 400nm-900 nm is tested.Based on GUM,the uncertainties in the measuring results are evaluated,and according to the grating grooves measured by AFM(Atomic Force Microscope),the theoretical diffraction efficiency is calculated.Next,the comparison between the theoretical calculations and the measuring results is carried out,and the reliability of the measurement system is illustrated.Finally,the measurement performance of the measurement system is analyzed,and the test results show that,the testing accuracy,the testing stability and the testing repeatability are 2.5%,0.085% and 3.5%,respectively.The research of this paper would provide technology support for the further manufacture of convex gratings and the development of imaging spectrometers.