Patent ID: 9726474
Date: 2017-08-08
CPC Classifications: G01B,G01S

Claim:
1. A method of measuring a change in an optical path length using differential laser self-mixing interferometry, the method comprising the steps of: obtaining a reference self-mixing interferometric signal (Sr) of a laser (LD) having a laser cavity; obtaining a main measurement self-mixing interferometric signal (Sm) of said laser (LD), once backscattered laser light (br) has re-entered said laser cavity, said backscattered laser light (br) being generated from the reflection on a target (T) of a main measurement laser light beam (be) emitted by said laser (LD) while is being modulated according to a specific modulation pattern; and determining the relative change in the optical path length between said laser (LD) and said target (T) comprised in a range between 0 and λ/2, by comparing the relative positions along time of fringes or transitions of said main (Sm) and reference (Sr) self-mixing interferometric signals; wherein the method is characterised in that said reference self-mixing interferometric signal (Sr) is obtained on said laser (LD) and at a different moment than said main measurement self-mixing interferometric signal (Sm) once backscattered laser light, generated from the reflection on said target (T) of a reference laser light beam (be) emitted by said laser (LD) while maintaining said specific modulation pattern while both the main measurement self-mixing interferometric signal (Sm) and the reference self-mixing interferometric signal (Sr) are acquired, has re-entered said laser cavity.