Optical EngineeringWavefront aberration measurement technology for microlenses using a Mach-Zehnder interferometer with effective apertures
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We describe the wavefront measurement interferometry technologies suitable for microlenses. It is common for microlenses to exhibit large aberrations and microlens arrays can introduce additional negative effects from the array when the wavefront aberration is measured. In the case of a microlens array, stray light may be generated by the rest of the microlenses during measurement. A single-pass interferometer, such as the Mach-Zehnder interferometer, is a good solution. It is sometimes difficult to maintain a conjugate condition due to large aberrations when a double-pass interferometer, such as a Fizeau interferometer, is used. Interferometers usually use a software aperture to define the calculation area for wavefront aberration measurement. But we determine the effectiveness of the hardware aperture in reducing the noise in the interferometer optics compared to the use of the software aperture. The result of a theoretical investigation shows the effects of the hardware, and the software apertures are almost the same. An experimental investigation is also made using a Mach-Zehnder interferometer with both hardware and software apertures. The hardware aperture is inserted into the interferometer optics and is projected to reduce the effective size of aperture on the pupil of the microlens to avoid the Fresnel diffraction. Finally, the theoretical and experimental results show good correspondence. We show the necessity of the wavefront aberration measurement interferometer technologies for microlenses.