Digital Holography Microscopy (DHM): Fast and robust systems for industrial inspection with interferometer resolution
With the recent technological advances, there is an increasing need for measurement systems providing interferometer resolution for inspection of large quantities of individual samples in manufacturing environments.. Such applications require high measurement rates, robustness, ease of use, and non-contact systems. We show here that Digital Holographic Microscopy (DIM), a new method that implements digitally the principle of holography, is particularly well suited for such industrial applications. With the present computers power and the developments of digital cameras, holograms can be numerically interpreted within a tenth of second to provide simultaneously: the phase information, which reveals object surface with vertical resolution at the nanometer scale along the optical axis, and intensity images, as obtained by conventional optical microscope. The strength of DHM lies in particular on the use of the so-called off-axis configuration, which enables to capture the whole information by a single image acquisition, i.e. typically during a few ten of microseconds. These extremely short acquisition times make DHM systems insensitive to vibrations. These instruments can operate without vibration insulation means, making them a cost effective solution not only for R&D;, but also especially for an implementation on production lines. Numerous application examples are presented in this paper such as shape and surface characterization of high aspect ratio micro-optics, surface nanostructures, and surface roughness.