Abstract
Abstract. The applications of freeform surfaces in optical components and systems are increasing more and more. Therefore, appropriate measurement techniques are needed to measure these freeform surfaces for verification. This task is still a challenge for most measurement techniques. In this paper, we propose a measurement technique for optical and other specular freeform surfaces based on experimental ray tracing. This technique is able to measure form and mid-spatial-frequency deviations simultaneously. The focus will be set on the sensing technique and the measurement uncertainties in the setup. As the measurement technique is described, an estimation of the influence of different uncertainties based on simulations is given. The result from an experimental measurement is evaluated in relation to the influence of the uncertainties. A comparison measurement for evaluation is given.
Highlights
Freeform surfaces are the level in the evolution of optical surfaces
The quality of the manufactured surfaces has to be verified to ensure the desired functionality in the optical system. We target this need for verification using a variation of the measurement technique called experimental ray tracing (ERT) (Häusler and Schneider, 1988)
This includes the precise measurement of the paraxial focal length of optical components (Binkele et al, 2016), the performance measurement of progressive addition lenses (Gutierrez et al, 2017a), the characterization of secondary optics for LEDs (Gutierrez et al, 2017b) and even the refractive index measurement in gradient-index lenses (Binkele et al, 2019a)
Summary
Freeform surfaces are the level in the evolution of optical surfaces. After spherical and aspherical surfaces, they open new degrees of freedom to design optical components (Thompson and Rolland, 2012). The original measurement system implemented by Ceyhan et al (2011) was already able to determine surface imperfections in the range of form and mid-spatial-frequency of spherical and aspherical lenses. These imperfections are derived from the determined optical function. We modified the principle of ERT in a way not to measure the surface under test (SUT) in transmission, but in reflection This opens the possibility of using the abilities of the sensing technique while overcoming the ambiguity in the measurement results
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