Measurement of transparent solution concentration using high sensitivity total-internal-reflection phase-shifting interferometry

• Main Author: 楊里霆
• Other Authors: 林俊佑
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/49921001911088520758

碩士 === 國立彰化師範大學 === 機電工程學系所 === 103 === In this paper, a high-sensitivity total-internal-reflection (TIR) phase-shifting interferometer is proposed for measuring the concentration of transparent solutions. A linearly-polarized expanding beam after passing through a Soleil-Babinet compensator and a spatial filter penetrates into a high-sensitivity TIR apparatus. The apparatus comprises a phase-level shifter (being formed by combining a half-wave plate and two quarter-wave plates that exhibit specific optic-axis azimuths), an isosceles right-angle prism whose base is directly contacted with a tested liquid, and an analyzer. The interference intensity of the TIR beam output from the apparatus is captured by a CCD camera. Using the four-step phase-shifting method by controlling the Soleil-Babinet compensator, the full-field phase difference used to determine the transparent solution concentration of the tested substance is obtained. Because the full-field phase difference exhibited by the transparent liquid concentration is associated with the azimuth angle of the analyzer transmission axis, both the high and low sensitivitymeasurement can be achieved by regulating the transmission axis. The resolution of3.19×10-4 RIU in low sensitivity and ¬¬¬¬¬¬¬¬¬2.38×10-5RIU in high sensitivity was achievable. In addition to high, tunable sensitivity and excellent resolution, the proposed approach also provides the advantage of high stability due to its common-path configuration.