Proceedings Article | 24 May 2018
KEYWORDS: Phase shifts, Interferometry, Vibrometry, Microscopy, Phase interferometry, Stereoscopy, Image resolution, Detector development, Sensors, Phase imaging
Parallel phase shift interferometric detection systems were developed using polarized interferometry, three detectors and multiple wavelengths. In phase shift interferometry (PSI) several phase shifted interference images are usually acquired in a sequence and are algebraically combined to extract the phase information. However, phase imaging is limited both by the 2π phase modulo limiting the ability to map structures with heights only up to half the source's wavelength i.e. several hundreds of nm, and also by error induced by the movements of the sample between the acquisitions of phase shifted interference images. Several approaches for dealing with these limitations have been developed that provided only a limited solution, e.g. using a beat wavelength interferogram by a two wavelength illumination but that is more sensitive to phase noise and thus less accurate and parallel PSI in which all phase shifted images are acquired simultaneously but that does not resolve the height limitation. We have developed a combined and improved technique for parallel PSI and three wavelength illumination enabling overcoming both limitations without elevating phase noise sensitivity. Several bench prototypes were built: some allowing video rate 3D imaging of moving samples such as biological live samples or high throughput scanning of metrology samples with nm scale resolution, and others allowing single point very high speed axial motion tracking and vibrometry with sub-nm scale resolution and max step height of few tens of µm.
Selected References:
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