Distance measurement by multiple-wavelength interferometry

Multiple-wavelength interferometry enables us to increase the range of non-ambiguity and to reduce the sensitivity of classical interferometry. It can also be operated on rough surfaces. The accuracy depends on the stability and the calibration of the different wavelengths. An electronically calibrated three-wavelength source for synthetic wavelengths in the millimetre range with an accuracy of better than 10(-5) has been demonstrated. Absolute distance measurements were performed up to 200 mm with a resolution of better than 10 mu m.