30 October 1998 Common-path heterodyne interferometer with automatic focusing system for online surface profiling
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A common-path heterodyne interferometer for on-line non- contact measurement of surface profile has been developed. A single-mode frequency-stabilized laser diode (780 nm) serves as the light source to make whole system compact (total volume 250L X 200W X 100Dmm). The optical common-path configuration remarkably minimizes the effects caused by vibration, air turbulence and other environmental variations. Multiperiodical phase measuring technique, which is based on the combination of fractional periodic phase measurement and integer periodic phase counting, is employed in signal processing, so the system features not only high vertical resolution but wide measuring range as well. In addition, the automatic focusing system greatly facilitates the measurement especially on-line profiling. This paper gives the brief principles, the arrangement of the interferometer and some test results. The system has vertical resolution of 0.39 nm and lateral resolution of 0.73 micrometer. The stability is 1.95 nm (3(sigma) ) during about 1 hour and the accuracy of automatic focusing system is 0.1 micrometer within plus or minus 25 micrometer of the focus.
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Rong Liang, Rong Liang, Dacheng Li, Dacheng Li, Mang Cao, Mang Cao, Hongzhi Zhao, Hongzhi Zhao, Yong-jun Wu, Yong-jun Wu, "Common-path heterodyne interferometer with automatic focusing system for online surface profiling", Proc. SPIE 3426, Scattering and Surface Roughness II, (30 October 1998); doi: 10.1117/12.328470; https://doi.org/10.1117/12.328470

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