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摘要:
为瞬态测量大口径光学元件波前,提出一种基于斜入射结构的近红外反射式错位点衍射干涉原理的Φ400 mm瞬态波前检测方法。该方案将待测光分成两束互相错位的参考光与测试光,从而在干涉图中引入高线性载频,采集到对比度良好的干涉图后,利用傅里叶变换相位解调法从单幅干涉图中提取待测波前相位,实现瞬态波前动态测量。实验光路总长近20 m,极易受气流的影响,且由于气流干扰随时间变化,该系统本身可以看作是大口径光学元件瞬态波前发生与检测装置。测试结果与SID4波前传感器比较,波前均方根(RMS)小于1/50 λ,可知所提方法可以实现大口径瞬态波前的高分辨率与高精度检测。
Abstract:In order to measure the instantaneous wavefront of large aperture optical elements, a method based on the structure of oblique incidence of reflective shearing point diffraction interferometer is proposed. A lateral displacement between the reference wavefront and the test wavefront is formed after passing this structure. The shear of two beams introduces linear spatial carrier frequency to the point diffraction interferogram. After receiving a good contrast interferogram, wavefront phase is retrieved by Fourier transform (FT) automatically to realize the dynamic measurement of instantaneous wavefront. The optical path is up to 20 m, so the air current is a significance factor to the result. Besides, because of the air current, the system itself can be seen as a instantaneous wavefront happening and measurement of large aperture optical elements. The results indicate that the root mean square value is in accord with that acquired by SID4 wavefront sensor (less than 1/50λ), so about the repeated accuracy. The method proposed can be applied in high resolution and accuracy measurement of instantaneous wavefront.
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Overview: In order to measure the instantaneous wavefront of large aperture optical elements, a method based on the structure of oblique incidence of reflective shearing point diffraction interferometer is proposed. In the measurement, the near infrared fiber laser, which operates at 1313 nm wavelength, works as a light source. The light beam transmits through the spatial filter to generate a standard spherical wavefront. The standard spherical wavefront passes through the beam splitter and then it reaches the off-axis parabolic mirror whose diameter is 400 mm and F number is 10. The off-axis parabolic mirror realizes the transformation between the convergent wavefront and the collimation wavefront. The collimated wavefront reaches back to the off-axis mirror after being reflected by the mirror under test. The wavefront to be measured is splitted into two parts. One part is reflected directly from the slit and form the wavefront to be measured, the other part transmits through the slit and is diffracted by the pinhole to get a standard spherical wavefront works as the reference wavefront.These two kinds of wavefront form interference fringe at the target surface of the CCD and the imaging lens images the location of the exit pupil. Because of the transverse dislocation of the two beams of light, high linear carrier frequency of the interferogram is introduced.The frequency of the linear carrier is set, by adjusting the incidence angle θ, near the Nyquist frequency as close as possible. After receiving a good contrast interferogram, wavefront phase is retrieved by Fourier transform (FT) automatically to realize the dynamic measurement of instantaneous wavefront. On the basis of scalar diffraction theory and Fourier optics theory, a theoretical model of instantaneous wavefront was established and formula of linear carrier was derived.Furthermore, to study the effect which the lateral and axial defocus of pinhole have on diffraction intensity and reference wavefront quality, a mathematical model of convergent beam diffraction by a pinhole is established based on Fresnel diffraction theory. F number of the converging beam, diameter of the pinhole and so on are also taken into account. The optical path is up to 20 m, due to the long cavity of the optical path, the air current is a significance factor to the result. Besides, because of the air current, the system itself can be seen as a instantaneous wavefront happening and measurement of large aperture optical elements. The results indicate that the root mean square value is in accord with that acquired by SID4 wavefront sensor (less than 1/50λ), so about the repeated accuracy. The testing method proposed can be applied in high resolution and accuracy measurement of instantaneous wavefront
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表 1 室温15℃、湿度50%情况下某次恢复的30组波面数据
序号 PV/λ RMS/λ 1 0.616 0.079 2 0.689 0.079 3 0.641 0.080 4 0.609 0.079 5 0.631 0.079 6 0.642 0.078 7 0.607 0.079 8 0.599 0.078 9 0.644 0.079 10 0.573 0.080 11 0.654 0.079 12 0.596 0.080 13 0.581 0.081 14 0.594 0.081 15 0.608 0.081 16 0.615 0.081 17 0.573 0.084 18 0.630 0.084 19 0.606 0.085 20 0.594 0.086 21 0.577 0.087 22 0.654 0.079 23 0.662 0.078 24 0.673 0.079 25 0.676 0.078 26 0.660 0.077 27 0.661 0.077 28 0.624 0.074 29 0.559 0.083 30 0.567 0.082 -
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