The azimuthal alignment and application of Photoelastic modulator system

• Main Authors: Charn-Kuo Wang, 王昌國
• Other Authors: Yu-Faye Chao
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/24126316753241355754

博士 === 國立交通大學 === 光電工程所 === 87 === Instead of the nulling method, we propose a high-level intensity technique to determine the relative azimuth orientation of a photoelastic modulator and an analyzer. In a photoelastic modulating system, one can obtain a DC intensity distribution by varying the phase modulation amplitude at two azimuth angles of the analyzer, which are p/4 apart from each other. The relative azimuth orientation can be determined by taking the ratio of the slopes of these two intensity distributions around the linear region of the zero point of the zero-order Bessel function. A similar technique is also applicable to wave plates and reflecting surface for aligning their optical axes and the plane of incidence with respect to the system. Adjusting the analyzer at 900 to the strain axis of a photoelastic modulator, one can determine the optical activity by measuring the slope of its DC intensity distribution under various phase modulation amplitudes. This technique was applied to measure the ellipticity of few quartz quarter-wave plates and the optical rotation of an optical active crystal. A multiple reflection enhancement effect in the wave plate was observed and discussed. By considering the photoelastic modulator as an elliptical retarder, we also determined its intrinsic ellipticity and static phase retardation, to increase the accuracy of measurements. We conclude that this high-level intensity technique is capable to align the optical elements, and can be considered as an alternative method to measure the optical activity in crystals, in which optical activity and birefringence coexist.