Two-Color Interferometry in the Mid-Infrared based on Quantum Cascade Lasers for Absolute Distance Measurement with Nanometer-Scale Precision

Laser interferometry enables measuring relative distance variations with an extreme sensitivity corresponding to a fraction of the considered optical wavelength, but has a very short unambiguous range of only half a wavelength. In this work, we investigated the use of two-color interferometry, a method in which the use of two different but close optical wavelengths enables the unambiguous range to be extended to a synthetic wavelength Λ much longer than the optical wavelength λ, allowing for absolute distance retrieval. We present a first demonstration of this method in the mid-infrared (MIR) based on the use of quantum cascade lasers (QCLs).