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

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 mu 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 P, we found possible to measure accurately the slopes of each face of the microstructures under investigation, and this with a good theoretical agreement.