# Large-Aperture Real-Time Compensated Collimating Wavefront Error Detection Method
## 1 Introduction  
A collimating system is an important part of an optical system. The collimated beam evaluation technology directly affects the wavefront quality of the collimating system, thus affecting the accuracy of the interferometry system. In recent years, a variety of methods for detecting collimated wavefront errors have been proposed, which include the Hartmann method [1], shearing point diffraction interferometry [2], and the pentaprism scanning method [3]. The pentaprism scanning method has been widely adopted to detect the emergent wavefronts of large-aperture optical collimating systems. This method can not only expand the range of the spatial measurement, but also improve the resolution and accuracy of the spatial measurement.  
[PERSON] used the pentaprism scanning method to detect wavefronts of small and medium apertures [4]. By scanning a finite number of wavefronts of wavelets that comprised a wavefront emergent in a certain direction, the slope change of each sample point was analyzed and used to reconstruct the wavefront under measurement. Researchers at the University of Arizona used pentaprism scanning technology for processing and inspecting 2 m flat mirrors [5]. [PERSON] et al. developed an off-axis surface test method based on pentaprism scanning and used it for National Institute of Standards and Technology (NIST) performance testing on the 8.4 m giant Magellan telescope [6]. The test method has also been used to measure low-order aberrations and has served as a verification test for full-aperture interferometer systems with large-aperture non-axisymmetric null correctors. [PERSON] et al. developed a testing system based on an electronic autocollimator, which consisted of a linear rail system, a scanning pentaprism, and an electronic autocollimator. Here, the accuracy of the system increased from 0.91\({}^{\prime\prime}\) to 0.36\({}^{\prime\prime}\) arcsec by calibration of the system error [7]. [PERSON] et al. built a scanning pentaprism system to be used as an absolute test for an optical flat. The light from an autocollimator was reflected from two pentaprisms to project reference beams of light onto a flat mirror. This provided informationon low-order optical aberrations in the flat mirror [8]. [PERSON] et al. developed a scanning pentaprism system that exploits geometry to measure off-axis paraboloidal mirrors, which was based on the property of a paraboloidal surface. They gave detailed performance results for the measurement of the 1.7 m mirror and the analysis for a test of the GMT segments [9]. [PERSON] et al. reported an improved single shot electrooptic sampling-based detection scheme to measure the time profile of a THz pulse using the inherent curvature of a converging wavefront, which used the converging wavefront [10]. [PERSON] et al. presented bandwidth enhancement and frequency scanning for a fan beam array antenna, utilizing a novel technique of band-pass filter integration for wireless vital signs monitoring and vehicle navigation sensors [11]. [PERSON] et al. presented a fast and accurate method to calculate the displacement errors caused by grating surface errors and line errors in a grating-based interferometer with a Littrow configuration. The diffracted wavefronts were used to calculate the displacement errors at the 1 st orders of the grating [12].