Integrated accuracy enhancement for the Fabry–Pérot interferometer: The multi-parameter approach series (MPAS)

Fabry–Pérot white light interferometry is at the heart of the surface force apparatus (SFA). One of the applications of SFA is the measurement of properties of sub-nanometer-confined fluids. For the determination of the properties of a confined fluid, the absolute accuracy of SFA is directly linked to the accuracy of the parameters describing the optical layers of the interferometer, particularly the micrometer thick mica spacer layers. During the measurement of nano-confined films, most of the optical path occurs within these mica spacer layers, which are thus identified as the major accuracy-limiting factor. This work describes an integrated accuracy enhancement method, the so-called multi-parameter approach series (MPAS), which is especially designed to determine the mica thickness and its dispersive refractive index in situ at enhanced accuracy, without the use of the conventional mica–mica contact calibration. We show how the proposed procedure increases the absolute instrumental accuracy by increasing spectral correlation. The proposed MPAS algorithm provides a significant accuracy enhancement and concurrently reveals the need to assess the elasto- and opto-mechanical properties of mica for any further accuracy improvements.