Comparison of two noise reduction methods in coherence scanning interferometry for surface measurement

Gomez, Carlos; Su, Rong; Lawes, Simon; Leach, Richard

Abstract

Coherence scanning interferometry (CSI) can measure relatively flat surfaces with sub-nanometre precision, but the measurement noise may increase significantly if the intensity of the interferometric signal reduces when measuring non-flat surfaces or surfaces with low reflectance. Furthermore, environmental vibrations may cause small changes in the positions of the optical and mechanical components in a CSI instrument, causing errors in the vertical sampling distance. Using low-pass or averaging filters may reduce noise by digitally smoothing the measured topography at the cost of lower lateral resolution. Alternatively, there are two physical methods to reduce measurement noise in CSI at the expense of longer data acquisition times: (1) average a sequence of repeated topography measurements, or (2) increase the sampling frequency of the fringe signal in the vertical direction during a single data acquisition-sometimes referred to as signal oversampling. In this paper, we compare these two methods by measuring a silicon carbide reference flat at 0° and 4° tilt angles. It is found that mechanical vibration of the system has a different impact on the measurement noise when using the topographic averaging and fringe signal oversampling methods.

Citation

Gomez, C., Su, R., Lawes, S., & Leach, R. (2019, September). Comparison of two noise reduction methods in coherence scanning interferometry for surface measurement. Presented at 14th International Symposium of Measurement Technology and Intelligent Instruments (ISMTII2019), Niigata, Japan

• Presentation Conference Type: Conference Paper (published)
• Conference Name: 14th International Symposium of Measurement Technology and Intelligent Instruments (ISMTII2019)
• Start Date: Sep 1, 2019
• End Date: Sep 4, 2019
• Acceptance Date: Jul 16, 2019
• Publication Date: Sep 4, 2019
• Deposit Date: Aug 14, 2019
• Peer Reviewed: Peer Reviewed
• Keywords: Measurement noise; coherence scanning interferometry; surface metrology
• Public URL: https://nottingham-repository.worktribe.com/output/2428323
• Related Public URLs: https://www.ismtii2019.jp/