Six European National Measurement Institutes (NMIs) have joined forces within the European Metrology Research Programme funded project NANOTRACE to develop the next generation of optical interferometers having a target uncertainty of 10 pm. These are needed for NMIs to provide improved traceable dimensional metrology that can be disseminated to the wider nanotechnology community, thereby supporting the growth in nanotechnology. Several approaches were followed in order to develop the interferometers. This paper briefly describes the different interferometers developed by the various partners and presents the results of a comparison of performance of the optical interferometers using an x-ray interferometer to generate traceable reference displacements.
An imaging spectrometer based on a Fabry-Perot interferometer is presented. The Fabry-Perot interferometer scans the mirror distance up to contact and the intensity modulated light signal is transformed using a Fourier Transform based algorithm, as the Michelson based Fourier Transform Spectrometers does. The resulting instrument has the advantage of a compact, high numerical aperture, high luminosity hyperspectral imaging device. Theory of operation is described along with one experimental realization and preliminary results.
A homodyne interferometer which exploits a multiple reflection arrangement between two quasi parallel mirrors to deliver a multiplication factor is presented. The relative displacement of the two mirrors causes a more than 100-fold increment of the optical path, which is measured by the optoelectronic circuitry. This leads to a proportional reduction of the errors associated with the subdivision of the optical fringes, with the effect of fringe nonlinearities, and with the opto-electronic noise. In particular the reduction of the electronic noise limit to the level of 20 fm Hz −1/2 has been demonstrated. The exact formula of the gain has been calculated and confirmed experimentally.
A method to amplify the rotation angle of a mirror, based on multiple reflections between two quasi-parallel mirrors, is presented. The method allows rotations of fractions of nanoradians to be measured with a simple setup. The working principle, the experimental setup, and the results are presented.
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