Measurement Of Coherent Transfer Function With Ptychographic Iterative Engine

With the rapid development and widespread application of new technologies such as machine vision and virtual display,a variety of unconventional optical imaging systems with different functions have emerged,and transfer function measurement as the "gold standard" for designing and detecting the performance of imaging systems is more important than ever.Traditional transfer function measurement methods include contrast method,pinhole method,slit method,knife-edge method,holographic interferometry,power spectroscopy,etc.Contrast measurement requires numerous samples and complex procedures;The pinhole method has low utilization rate of light intensity,and the knife-edge method relies on differential calculation,and both are susceptible to noise.Holographic interferometry is not only significantly affected by noise,but also requires high-quality reference light;Power spectroscopy data processing is complex and measurement bandwidth is limited.In order to develop a transfer function measurement technology with simple optical structure,convenient measurement and high accuracy,this paper imposes the pinhole of the imaging system to be measured under the condition of coherent light illumination,records the defocused spot in the defocused position,and proposes a highly curved illumination PIE technology to reconstruct the light field distribution on the light field surface of the imaging system,and calculate the coherent transfer function of the imaging system.On the basis of theoretical analysis,this paper verifies the proposed method from the aspects of numerical calculation and experimental measurement,and the results show that the proposed method has the advantages of short measurement optical path,high measurement accuracy and convenient operation,and the following work is mainly carried out:(1)Overcoming the phase underresolution problem of traditional PIE imaging under highly curved illumination conditions,high-precision PIE imaging under highly curved wavefront illumination conditions was developed.The Fresnel diffraction of the transmitted light can be used as the Fourier transform of the equivalent transmitted light,to avoid considering the under-resolution problem of wavefront curvature and realize PIE high-resolution imaging under highly curved illumination.(2)The imaging system to be measured imaged the pinhole,and the light field phase on the sample surface is reconstructed by using the highly curved illumination PIE imaging method,to realize the transfer function measurement of the short throw imaging system,which changes the problem that the traditional PIE imaging needs to be attached to the beam adjustment system and the optical path is too long when it is used to measure the short throw system.(3)An experimental system was built and the measurement results were compared with real data,which verified the technical applicability of the proposed method.The cylindrical mirror with known curvature is placed at the pupil outlet of the system to be measured,and the pupil exit function with or without a column lens is measured by the highly curved illumination PIE technology proposed in this paper,and then the wavefront difference between the two is calculated,and the wavefront difference is decomposed by Zennick,which verifies the high measurement accuracy of the proposed method.