In the present study, we proposed a new type of autocollimator for high-accuracy
angular measurement within a large angle range. The new system
comprises a traditional autocollimator and Risley prisms, and it
employs the normal tracing method to measure the angle. By rotating
the Risley prisms, the outgoing beam of the autocollimator can be
deflected close to the normal direction of the reflecting mirror and
then reflected back to the system by the mirror along the near normal
direction to realize normal tracing. Based on the angle measured by
the autocollimator and the rotation angles of Risley prisms, we can
calculate the tilt angle of the mirror. Since the beam returns to the
system close to the original path, the angle error caused by
aberration, optical component processing defects, nonuniform
refractive index, and so on, can be ignored. Due to the normal tracing
measurement method, theoretically, the angle error is not affected by
the working distance. ZEMAX non-sequential simulation shows that the
angle error caused by aberration in the new system can be
significantly reduced.
Scanning deflectometric profilers based on an f-θ system are typical optical tools used to measure mirror profiles at many synchrotron facilities. Unlike these profilers, which are based on a pencil beam, here a secondary light source and a pinhole are used to construct a system that automatically selects a beam that will always pass through the pinhole and propagate along the normal direction of the measured area on the surface under test. By measuring the angle variation of the selected beam, slope variations of the surface under test can be measured. Systematic errors introduced by manufacturing defects or aberrations of an optical element, which greatly degrade the performance of traditional profilers, could be minimized by using the developed method. Simulation values of the proposed method and a conventional method are compared.
.The normal tracing angle measurement system based on Risley prisms can eliminate the influence of aberrations other than the dispersion of Risley prisms on the angle measurement accuracy. Although the traditional dispersion optimization method based on the extreme point can make the beam directions of different wavelengths more consistent after passing through the Risley prisms, the light intensity distribution that deviates from the extreme point wavelength causes the spot centroid to deviate from the target position, thus introducing the angle measurement error. In this paper, we propose a highly symmetry-glued achromatic Risley prisms optimization method for the needs of a normal tracing angle measurement system. Our method not only realizes the beam direction as closely as possible after the deflection of the Risley prisms but also compensates for the centroid error caused by the beam deviating from the central wavelength. ZEMAX simulation shows that, in the normal tracing angle measurement system, within the angle measurement range of ±700 ″ and the light source wavelength range of 600 to 700 nm, the angle measurement error introduced by the dispersion of the optimized Risley prisms is not >0.01 ″ .
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