Advances in Research on Curvature Sensors to Improve Dynamic Real-Time Measurement
February 08, 2023
[ Instrument Network Instrument R & D ] In recent years, the adaptive optical system has continuously increased the requirements for dynamic real-time measurement to better adapt to the fields of high-energy lasers, astronomical observations, and optical communications. Recently, Zhang Junyong's group of the Shanghai University of Optics and Fine Mechanics Joint Laboratory of High Power Laser Physics used the Fibonacci photon sieve to realize single exposure wavefront diagnosis and imaging of curvature sensing. , 115, 234101 (2019)].
It is reported that the curvature wavefront sensor is a promising new wavefront sensor in adaptive optics. It measures the local curvature of the wavefront inside the pupil and the normal slope on the edges. The output signal provides sufficient information for the reconstruction of the wavefront. This novel wavefront sensing technology quickly gained attention and has been practically used in white adaptive telescope systems.
Unlike wavefront sensing technology based on the wavefront slope, curvature sensing is the second derivative of the wavefront, and its relationship with the phase distribution satisfies the Poisson equation, and the relationship between the control signal and the deformation of the deformable mirror also exactly meets the equation . Using this feature, the response matrix control method can be used to directly control the curvature-type anamorphic mirror without calculation, which shortens the response time of the adaptive system and improves the online real-time performance of the adaptive system.
Wavefront curvature sensing is to obtain the curvature and phase distribution of the wavefront by measuring the light intensity distribution on the defocused surface. To achieve a single measurement, at least two layers of light intensity before and after the focal plane need to be recorded simultaneously. The amplitude Fibonacci photon sieve has the function of three-dimensional array diffraction limit focus. Through the multiple identical copies of the object to be measured, the intensity map distributed in the axial direction is mapped to the radial orientation. A single exposure of a single detector can achieve multiple Simultaneous recording of different transmission surfaces, which avoids the time-sharing multiple exposures commonly used for curvature sensing.
In addition, wavefront curvature sensing uses diffraction theory to calculate the light intensity distribution on the two defocus surfaces, so as to obtain the wavefront curvature and the wavefront radial tilt of the aperture edge. According to the differential characteristics of Zernike polynomials, two different methods are used to deal with curvature and tilt respectively, and the integral method is used to solve the problem that the 8 function is difficult to handle on the boundary. The control matrix is ​​calculated in advance from the geometrical distribution of the detector, and the wavefront is reconstructed using the Zemike polynomial curve fitting method. Computer simulation shows that the wavefront residual is less than 5%, which verifies the feasibility of this wavefront reconstruction algorithm.
Shanghai Institute of Optics and Mechanical Engineering actively promoted the transfer of scientific and technological achievements and provided technical support for the adjustment and upgrading of local industrial structures, and achieved significant results. The Shanghai Advanced Laser Technology Innovation Center, co-constructed by Shanghai Opto-Mechanical Research Institute and the local area, has been completed and gradually put into use, and the Nanjing Advanced Laser Technology Research Institute has become a domestic intelligent laser manufacturing technology public service platform to fully serve the integrated development of the Yangtze River Delta.
Source: Baidu Academic, Shanghai Institute of Optics and Electronics
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