Fast high-precision distance measurements with electro-optic frequency combs

Non-contact distance measurements on scattering surfaces with short acquisition times are of great importance in industrial metrology. This requires highly sensitive detection schemes that maintain precision over a large range of received power levels. In this context, frequency combs (FC) based on femtosecond lasers have emerged as valuable tools. However, while considerable technical effort is required to ensure stable operation of femtosecond lasers in an industrial environment, the achieved sub-µm precision is not necessary in many applications. Here we demonstrate that optical distance measurements to scattering metal surfaces can also be performed using continuous-wave lasers and electro-optic modulators for FC generation. We generate spectrally flat FC with 40 GHz line spacing defined by the modulator driving frequency. No knowledge of the absolute optical wavelengths is needed in this scheme. We obtain measurement errors of less than 3 µm in an acquisition time of only 8.3 µs, and a measurement error of less than 10 µm can be maintained over a dynamic range of more than 37 dB. Profile measurements on a technical part agree well with tactile reference measurements.