The extended surface forces apparatus. Part I. Fast spectral correlation interferometry

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Abstract
This article describes details of the operation and performance of fast spectral correlation interferometry, which allows for considerably improved operation of the surface forces apparatus. Up to 150 interference fringes can be simultaneously tracked over a wide spectral range, leading to considerably more precise and simultaneous extraction of multiple optical quantities, over a greatly extended distance range. When used for surface-separation measurement, a precision of 25 pm is readily achievable over a distance ranging from 0 to >10 μm. Data acquisition rates are also considerably improved, allowing for dynamic measurements. Automated actuation of optical deflectors introduces a multidimensional scanning capability to the optical probe with a lateral resolution of 1 μm. The entire process is computer controlled and features unattended batch processing of complex measurements. This publication illustrates experimental setup, methodology, measurements, and detailed error calculation for a selection of practically relevant situations in the extended surface forces apparatus.