Advances in indirect optical geometry measurement

Abstract This work investigates three approaches of indirect optical geometry measurement (InOGeM) based on fluorescent media in combination with confocal microscopy, aiming to overcome the limitations of conventional methods such as white light interferometry for optically uncooperative surfaces. The studied approaches comprise a homogeneous fluorescent medium, a multiple-particles aerosol, and a single-particle with optical tweezing. All approaches enable nearly complete surface acquisition, even for high surface tilts and low backscattered signals. The homogeneous medium provides high measurement speed and robust signal evaluation but suffers from unavoidable contamination of the sample. The multiple-particles approach reduces contamination effects, at the expense of decreased accuracy and increased signal processing complexity due to stochastic particle behavior. The single-particle approach achieves superior axial resolution and offers super-resolution potential, but is yet limited by a small measurement volume and low acquisition speed. Compared to white light interferometry, which was able to capture only less than 20 % of the surface in a highly tilted test region of a Fresnel lens, the indirect methods achieve measurability of up to 100 %. The axial resolution ranges from 684 nm (homogeneous medium) to 2.58 µm (multiple-particles) and down to 181 nm (single-particle), demonstrating the capabilities of precise indirect optical geometry measurements.