Measurements of corner cubes microstructures by high-magnification digital holographic microscopy

Abstract

This paper presents Digital Holographic Microscopy (DHM) quantitative measurements of transparent high aspect-ratio microstructures. Our experiment was performed using a digital holographic microscope in transmission configuration with a 60x magnification 1.3 NA oil immersion microscope objective, with a diode laser source at 664 nm. We used a calculation model based on the use of two immersion liquids for the experiment, the first one to resolve the phase jumps by using a refractive index liquid close to the sample index, in combination with a second one to retrieve the sample topology from the optical path length information. Such a model makes absolute topographic measurements of high aspect ratio transparent samples achievable by DHM. The model is then applied to measure 25 and 50 m transparent micro-corner cubes arrays, which exhibit up to 1:1,4 aspect ratio with theoretical slopes up to about 55 degrees. Thanks to our phase measurement precision down to 1°, we found possible to measure accurately the slopes of each face of the microstructures under investigation, and this with a good theoretical agreement.