Stabilized three-wavelength source calibrated by electronic means for high-accuracy absolute distance measurement

Multiple-wavelength interferometry offers great f lexibility in working distance and sensitivity by permitting an appropriate choice of the different wavelengths used, and it can be operated on rough surfaces. The accuracy of distance measurement with this approach depends on the stability and the calibration of the different wavelengths. A novel concept of a multiple-wavelength source that uses laser diodes has been developed. It allows one to obtain an absolute calibration of the synthetic wavelengths by the use of electronic beat-frequency measurements. Experimental results show that a calibration of the synthetic wavelength in the millimeter range with an accuracy of better than 10(-5) is feasible.