Novel non-guideway laser interferometer for absolute long distance measurement

A novel non-guideway laser interferometer for absolute long distance measurement is presented. An external cavity diode laser (ECDL) shows great selectivity to its wavelength, with a bandwidth less than 100 kHz and a coherent distance of about 1000 m. The wavelength can be continuously tuned from 1495 nm to 1645 nm. These two characteristics enable a wavelength-tuning interferometry for absolute long distance measurement. In the interferometry for measuring the distance of L, the resolution and uncertainty could be 3 nm and 2.5 × 10^-6 L respectively, when the measuring range is about 100 m. In order to improve accuracy, exact fraction method can be applied employing several specific wavelengths. By this means, the uncertainty could be up to 5 × l0^-7 L.