Cost-effective laser feedback sensor for nanometric scale acoustic perturbations

In our earlier work, we introduced and demonstrated continuous wave frequency modulated differential optical feedback to measure low-frequency vibrations with displacements lower than half of emission wavelength of the laser. Using modulated optical feedback interferometry on perturbations whose amplitude was smaller than half the emission wavelength of the laser, the proposed sensor-enabled nanometric scale amplitude measurements from the shift in fringes that appear in a vibrating target by comparing them with the fringes on the stationary target. We extend the application of the technique to noncontact measurement of surface perturbations generated by acoustic beams. First, the displacement of the acoustically perturbed membrane of the transducer at a frequency of 26 kHz with an amplitude of 101 nm (lambda/10) is performed using a single laser diode in a point-and-measure fashion. Once the acoustic waveform has been characterized, the instantaneous surface displacement of a remote aluminum plate due to acoustic pressure is measured using the same setup, yielding a value of 75 nm. As a consequence, an application of a very cost-effective, noncontact, and high accuracy sensor based on the laser diode under optical feedback has been presented. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).