Investigation of factors affecting sensitivity enhancement of an optical fiber probe for microstructure measurement using oblique incident light

Recently, the demand for accuracy measurement of microstructures has been remarkable. We have been developing a measurement system for microstructures using a stylus made of an optical fiber and prisms. In this measurement system, the oblique irradiation of the laser beam was employed to detect the displacement of the stylus shaft generated by contact between the stylus tip and the measured surface, and to expand the measurable area and depth. After these evaluations, we discovered that the sensitivity was enhanced with the increase in the incident angle of the laser beam on the stylus shaft. Therefore, in this study, we focus on the effect of the incident angle of light on the measurement sensitivity. First, the enhancement sensitivity is confirmed by using the basic experimental apparatus. Next, the relationship between the incident angle of the laser beam and the sensitivity is theoretically examined using the 3D ray-tracing method. Finally, the factor of the sensitivity enhancement is analyzed using the same method. As a result, it was confirmed that the sensitivity was enhanced with the increase in the incident angle of the laser beam on the stylus shaft.