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Measurement Method of Curvature Radius of Spherical Mirror Based on Pinhole Point Diffraction Interferometer

A technology of curvature radius and measurement method, applied in the field of optical measurement, can solve the problems of low measurement accuracy and limited measurement accuracy, and achieve the effect of avoiding influence, synchronizing measurement and avoiding damage

Inactive Publication Date: 2017-06-27
NANJING UNIV OF SCI & TECH
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Problems solved by technology

In 2011, Hengyu Yi designed a set of compensation devices, using ZYGO interferometer to measure the radius of curvature of the mirror, using a compensation device can simultaneously realize the measurement of concave and convex mirrors, but the compensation is ignored in the process of calculating the radius of curvature The measurement error introduced by the thickness of the device makes the measurement accuracy limited
In 2012, Abdelsalam used a synchronous phase-shifting interferometer to measure the radius of curvature, which is a new non-contact measurement method, but the measurement accuracy is not high

Method used

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Embodiment

[0082] In the embodiment, the method of the present invention is used to detect the radius of curvature and surface profile of the two aluminum-coated spherical mirrors sequentially. The initial values ​​of the radius of curvature of the two mirrors are R=-220mm,-402mm. Polarization frequency stabilized helium-neon laser 1 has a working wavelength of λ=632.8nm, power of 1.5mw, and output spot diameter of φ1mm. The beam is reflected by the plane mirror 2, and the beam spot diameter is φ8mm after passing through the 8× laser beam expander 3. After the magnification 20 × , NA=0.42, working distance 20.68mm, the microscope objective lens 4 converges, and the focal point is projected onto the pinhole reflector 5, and the incident beam is diffracted by the pinhole to obtain a nearly ideal spherical wave.figure 1 The plate substrate of the middle pinhole reflector 5 has a thickness of 200 μm, on which a metal Cr film with a thickness of 200 nm is plated, and a φ1 μm diffraction pinhol...

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Abstract

The invention discloses a device and method for measuring the curvature radius of a spherical mirror based on a pinhole type point diffraction interferometer. Double quantitative defocusing is realized through sequentially inserting two parallel flat plates with different thicknesses in an interfering cavity of the pinhole type point diffraction interferometer. When the parallel flat plates are not placed in a test optical path, wavefront data W0 are obtained through phase shifting measurement. After the two parallel flat plates with different thicknesses are respectively placed in the test optical path, two different wavefronts W1 and W2 are obtained through phase shifting measurement, and the calculating formula of the curvature radius of the spherical mirror is derived through the difference between the defocusing coefficients of the W1 and the W0, the difference between the defocusing coefficients of the W2 and the W0 and a Gaussian imaging formula. When the non-contact type measurement method is adopted, the damage of the surface of the spherical mirror is avoided, a feasible method is provided for the non-destructive measurement of the curvature radius of the spherical mirror with a large numerical aperture. Meanwhile, the method is suitable for the surface shape test of the spherical mirror with the large numerical aperture.

Description

technical field [0001] The invention belongs to the technical field of optical measurement, in particular to a device and method for measuring the radius of curvature of a spherical mirror based on a pinhole type point diffraction interferometer. Background technique [0002] Spherical mirror is a common optical element in optical system and has important applications in various optical systems. For example, in the next-generation lithography projection objective lens system (Extreme Ultra-violet, EUV for short), a 13.5nm total reflection lithography objective lens is used. The system contains 6 pieces of off-axis spherical or aspheric mirrors, and the processing quality of the spherical mirrors has a key influence on the imaging effect of the entire system. The radius of curvature (ROC) is an important parameter to characterize the optical properties of an optical spherical mirror. The radius of curvature of the spherical mirror has a great influence on the imaging qualit...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01B11/255
Inventor 高志山田雪杨忠明王凯亮王帅成金龙叶井飞袁群
Owner NANJING UNIV OF SCI & TECH
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