Frequency Scanning Interferometry

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Frequency Scanning Interferometry (FSI) is a method of accurately measuring distance between two points that uses lasers set up in such a way as to form an interferometer.

The technique works by measuring the relative optical path differences of two interferometers. One interferometer is held at a constant length in a stable environment, and forms a reference length. The length of the second, measurement, interferometer is determined from knowledge of the length of this reference, and the length ratio of the two interferometers.

The ratio of the interferometers' lengths is measured using a frequency scanning laser. The frequency of the laser is scanned over a frequency range. This has the effect of modulating the received intensity of the reference and measurement interferometer in a fringe pattern. The ratio of the number of fringes observed in the measurement and reference interferometers is equal to the ratio of the lengths of the measurement and reference interferometers.

[edit] Uses

An FSI system is being used to monitor the relative orientation of the inner semiconductor tracker on the ATLAS detector at CERN.

[edit] References

• [1]
• P A Coe, D F Howell and R B Nickerson "Frequency scanning interferometry in ATLAS," Measurement Science and Technology, 15 (2004), 2175