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30 November 2009 The measurement of refractive index homogeneity of the large diameter Ge plate using interferometry
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Abstract
The method is presented to measure the homogeneity of the refractive index of infrared optical material, germanium (Ge) plate, using infrared interferometer working at 10.6μm. In order to measure the refractive index homogeneity of large diameter infrared material, the infrared standard lens is used in the test arm of infrared interferometer. The Ge plate is placed in the infrared spherical wave brought by infrared standard lens. The difference is measured between the wavefront with Ge plate and the one without Ge plate by the infrared interferometer working at 10.6μm. The addition aberration caused by Ge plate needs to be eliminated with Zernike polynomials fit from the results. As the Ge plate is too soft to process, its surface form may not meet the requirement for the measurement. In order to improve the measuring accuracy of the refractive index homogeneity, the surface deformations of two boundaries of the Ge plate are measured by phase-shifting digital interferometer working at 0.6328μm. The surface deformations are removed from the result of the refractive index homogeneity measurement. In this way, the measuring accuracy of the refractive index homogeneity is up to 10-5. A piece of Ge plate is tested. The peak-valley (PV) value of its refractive index deviation is 3.65×10-5, and the root mean square (RMS) value is 4.11×10-6.
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Jun He and Lei Chen "The measurement of refractive index homogeneity of the large diameter Ge plate using interferometry", Proc. SPIE 7506, 2009 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments, 750623 (30 November 2009); https://doi.org/10.1117/12.838104
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