High-accuracy length metrology using multiple-stage swept-frequency interferometry with laser diodes

Abstract

The optical length of a 1 m Fabry-Pérot etalon has been determined by swept-frequency interferometry using laser diodes. The method involves progressively building up the measurement accuracy using frequency sweeps over increasing ranges, from 150 MHz (one optical fringe) to 19 GHz and 7 THz. The 7 THz sweep is referenced to the splitting of the rubidium D lines at 780 nm and 795 nm. The result from the 7 THz sweep is sufficiently accurate to use the known frequency of either end point of the scan to determine the length to a few parts in , without the need for any further measurement. The scope for further development of this technique to a range of interferometric systems is discussed.

High-precision absolute distance measurement using dual-laser frequency scanned interferometry under realistic conditions

“…Absolute distance measurements using FSI under controlled conditions have been reported previously [8][9][10][11][12][13] by other research groups. Another proposed method for absolute distance measurement with comparable expected precision is based on a phase-stabilized femtosecond laser, using combined time-of-flight information and coherent, fringe-resolved interferometry [14].…”

Displacement Measurement

“…Consider the case of a laser diode aligned to an interferometer of free spectral range, ν R . If the output of the laser is scanned through a frequency range ν s , N fringes are generated at the output of the interferometer [31]. Provided the frequency scan range is accurately known, the free spectral range and hence the optical path length, L, may be determined from counting the number of fringes.…”

Theoretical Considerations on Combined Optical Distance Measurements Using a Femtosecond Pulse Laser

“…However, typical homodyne/heterodyne interferometry can measure displacements and it has the limitation for measuring absolute distance measurements due to its short unambiguity range determined by the used wavelength. To avoid the ambiguity problem in displacement interferometry, various research including synthetic wavelength interferometry [1], a frequency modulated continuous wave method [2], multiple wavelength interferometry [3], and frequency sweeping interferometry [4] have been applied to extend the unambiguity range. Recently, the application of a femtosecond pulse laser for distance metrology not only offers further improvements but also makes it possible to measure absolute distances precisely from industrial applications to space programs [5][6][7][8][9][10][11].…”