Laser self-mixing interferometric sensors

Laser feedback interferometry is being applied both to technical problems in mechatronics and to fundamental issues in laser dynamics. In the first case, with the aim of providing efficient and cost effective solutions for contactless measurements. In the second case, as a powerful investigation tool of the manifold realm of nonlinear laser dynamics.

Laser-self-mixing (LSM) was soon discovered as a promising candidate to replace interferometers in almost every application where a precision optical measuring system were required for the measurement of displacement, distance, velocity, vibration amplitude. In spite of its simplicity and the many proved realizations, laser-self-mixing has not yet sprang off a relatively small scientific community, possibly because of the onset of periodic and even chaotic instability in the diode-based LSM sensors for a sufficient feedback power.

In our laboratory we are exploring, both theoretically and experimentally, the origin of those instabilities in state-of-art lasers, like THz and mid-IR Quantum Cascade Lasers, with the aim to overcome one of the main drawbacks of LSM.

In addition, a number of new and potentially marketable applications of LSM have been developed by our group: a modular (up to six degrees-of-freedom simultaneously) motion sensor for correcting the off-axis deviations of a long linear slide displacement; a fiber LSM sensor for measuring the integral strain, as opposite to the local strain measured by point-like FBG sensors and the first real-time ablation-depth profiler based on LSM, in both semiconductor diode lasers and quantum-cascade lasers.