Apparatus for measuring the uniformity of the optical transmittance of a semispherical surface at normal incidence

TL;DR

This paper presents a novel apparatus combining traditional photometry and custom mechanics to accurately measure the optical transmittance uniformity of semispherical surfaces at normal incidence, improving measurement reliability.

Contribution

The paper introduces a new measurement system with a specialized mechanical structure and alignment process for precise transmittance uniformity assessment of hemispherical surfaces.

Findings

Successfully characterized transmittance uniformity of optical glass

Achieved a repeatability error of 0.026% in measurements

Solves limitations of traditional spectrophotometers for hemispherical surfaces

Abstract

In this paper, we build an apparatus for measuring the optical transmittance and its uniformity for a semispherical surface at normal incidence; the system is primarily comprised of a traditional double-beam photometric framework and a novel custom-made mechanical structure with multidimensional degrees of freedom. During the measurement process, a key aligning step is adopted to guarantee that the center point of the semispherical surface stands still in the light beam while scanning the hemispherical optical element point by point around the horizontal and vertical axes, which ensures that the laser beam is always normally incident onto the surface of the hemisphere. The experimental results show that the uniformity of the optical transmittance for a semispherical optical glass can be successfully characterized by the system, with a three-cycle repeatability error of 0.026% being demonstrated. Our system solves the problem of traditional spectrophotometers when measuring the spectral property of a hemispherical surface and thus can be popularized in similar applications.