Profile measurement of aspheric surfaces using scanning deflectometry and rotating autocollimator with wide measuring range

Abstract

High-accuracy aspherical mirrors and lenses with large dimensions are widely used in large telescopes and other industry fields. However, the measurement methods for large aspherical optical surfaces are not well established. Scanning deflectometry is used for measuring optical signals near flat surfaces with uncertainties on subnanometer scales. A critical issue regarding scanning deflectometry is that high-accuracy autocollimators (AC) have narrow angular measuring ranges and are not suitable for measuring surfaces with large slopes and angular changes. The goal of our study is to measure the profile of large aspherical optical surfaces with an accuracy of approximately 10 nm. We have proposed a new method to measure optical surfaces with large aspherical dimensions and large angular changes by using a scanning deflectometry method. A rotating AC was used to increase the allowable measuring range. Error analysis showed that the rotating AC reduces the accuracy of the measurements. In this study, we developed a new AC with complementary metal-oxide semiconductor (CMOS) as a light-receiving element (CMOS-type AC). The CMOS-type AC can measure wider ranges of angular changes, with a maximum range of 21 500 μrad (4500 arcsec) and a stability (standard deviation) of 0.1 μrad (0.02 arcsec). We conducted an experiment to verify the effectivity of the wide measuring range AC by the measurement of a spherical mirror with a curvature radius of 500 mm. Furthermore, we conducted an experiment to measure an aspherical optical surface (an off-axis parabolic mirror) and found an angular change of 0.07 rad (4 arcdegrees). The repeatability (average standard deviation) for ten measurements of the off-axis parabolic mirror was less than 4 nm.

An Efficient Automotive Paint Defect Detection System

“…Many different deflectometry methods are proposed for surface profilometry and defect detection. Some of these include Moier deflectometry [12][13][14][15][16], Ronchi method [17,18], laser scanning deflectometry [19][20][21], and phase measuring deflectometry (PMD) [11,[22][23][24].…”

Error compensation for long-distance measurements with a photoelectric autocollimator

“…7 Because the measurement range of the photoelectric autocollimator is closely related to the measurement distance, 8 long-distance and wide-range autocollimator has become a significant research focus in recent years. [9][10][11][12][13] Chen et al 12 proposed an angle measurement method based on optical frequency domain and realized a measurement range of 21,600 arc sec. Li et al 9 employed a cube corner as a reflector to extend the angle measurement range from 1.2 deg to 12 deg with an accuracy better than 35 arc sec.…”

An optical angle sensor based on chromatic dispersion with a mode-locked laser source

“…Where f is a focal length of the collimator objective. With the employment of a charge coupled device (CCD) as the photodetector of an optical angle sensor based on the laser autocollimation, a wide measurement range of over 1000 arc-seconds can be achieved (Ishikawa et al, 2014), while its measurement sensitivity becomes in proportion to f. On the other hand, in the case where a photodiode is used as the photodetector, the measurement sensitivity becomes independent from f, and an optical setup based on the laser autocollimation can be designed in a compact size (Saito et al, 2007). According to the previous study by the author's group, the sensor sensitivity S, which represents the degree of the change in photodiode output with respect to the change in angular displacement of a target of interest, becomes independent from f and can be given by the following equation (Saito et al, 2007;Gao, 2010):…”