Frequency Scanning Interferometry - a Versatile, High Precision, Multiple Distance Measurement Technique

Frequency Scanning Interferometry (FSI) has been developed for high precision, simultaneous, absolute distance measurements along multiple lines of sight. In the ATLAS semiconductor tracker, FSI will be used to measure lines of sight between nodes of a geodetic grid, attached to the support structure. Movements of the detector modules on the order of ten microns will be monitored by measuring changes in grid line lengths on the order of one micron. In this paper, the FSI technique is explained and FSI measurement results, demonstrating achievement of the required precision, are presented. These measurements have been made using interferometer components of the final ATLAS design. This interferometer design complies with the following requirements: low mass, rugged, radiation hard, able to fit into the small spaces allocated and insensitive to all conceivable changes in interferometer alignment. Future plans for using FSI within alignment systems for survey and operation of the next generation of linear colliders will also be discussed.