Optical feedback Interferometry for acoustic measurement and flow characterization
Optical measurements of physical quantities in fluid mechanics and acoustics represent an attractive field of research because of the possible applications. Indeed, these measurement techniques can be non-intrusive, unlike techniques using microphonic antennas or probes. In particular, they avoid the phenomena of acoustic diffraction or aliasing.
For acoustic measurement, the physical phenomenon exploited is the acousto-optic effect, where the propagation of an acoustic wave disturbs the refractive index of the medium in which the light waves propagate. With the help of optical interferometry techniques, it is then possible to visualize and even make quantitative measurements of an acoustic field.
However, one of the disadvantages of many of these optical methods is their difficulty of implementation: many optical elements, precision of alignment, high cost, etc. Methods that are simple to implement are therefore to be preferred for industrial applications. Among them, optical feedback interferometry seems to be a wise choice. This technique is inexpensive, requires a minimum of equipment and is easier to implement. It is based on the characteristics of laser diodes and their driving mode.
Recent works apply this technique to the characterization of flows in microchannels, or to the visualization and characterization of acoustic fields. It is in this context that this thesis is offered.
By exploiting the acousto-optic effect, the research will first be oriented towards applications for the very high frequency calibration of MEMS microphones for aeronautics: an optical feedback interferometer is currently being designed in the laboratory for this purpose. Then, the characterization of non-linear acoustic sources will be considered, in particular the shock wave produced by an electric arc source. Indeed, this type of source makes it possible to study in laboratory, under controlled conditions, the physics of the shock waves met in real situation: supersonic bang, noise of projectile. It will then be considered to develop networks of interferometers for the characterization techniques of acoustic fields by tomography, holography or inverse problem. The study of turbulence and noise of compressible flows is targeted.
