Comparison of the performance of the next generation of optical interferometers

Abstract

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.

Dimensional stability validation and sensor calibration with sub-nanometer accuracy

“…State-of-the-art lock-in detection instrumentation may be applicable. However, FPGAbased digital phase detection together with fast digitizers may outperform lock-in solutions in terms of sampling rate for a given phase sensitivity, digital noise filtering and high bandwidth common-mode noise suppression for sample and heterodyne reference signals [3,13]. The latter is of specific importance for the presented drift measuring interferometer.…”

“…Non-contact optical heterodyne, homodyne and phase shifting interferometry minimize the perturbation on the sample under test and provide high sensitivity, that scales with the optical wavelength [3][4][5][6]. Versatile configurations and large displacement range are supported.…”

Displacement Measurement

“…In some cases, where an un-polarised beam is used [11], a coating is applied to the beam splitter to give the required phase shift [12]. After traversing their respective paths, the two beams re-combine in the beam splitter to produce an interference pattern.…”

“…The flexure stage has a range of a few micrometres and is driven by a PZT. X-rays are incident at the Bragg angle [12] on lamella B, and two diffracted beams are transmitted. Lamella A is analogous to a beam splitter in an optical interferometer.…”

A low noise laser interferometry readout for challenging acceleration measurements in space

“…Typically, the displacement measurement is made with a capacitive sensor with a first armature fixed to the cage, the second one being the mass itself, which is made of, or properly coated with metal [1,2,3]. Laser interferometers have demonstrated to be able to measure displacements with accuracies to the level of the picometer [4] and their use is foreseen in high-resolution measurement in space [5]. Today's laser sources -such as solid state diode pumped lasers, extended cavity diode lasers or fiber lasers-can be integrated in compact subsystems suitable for space missions.…”