Characterization of the photo-EMF response for laser-based ultrasonic sensing under simulated industrial conditions

Summary form only given as follows. There is a desire in manufacturing environments to nondestructively evaluate components and control processes in real time. Laser-based ultrasound has the potential to be a robust diagnostic for many applications. A simple and inexpensive sensor based on the photoinduced-electromotive effect has been demonstrated to be functional under a variety of manufacturing conditions. To optimize the detector performance, a parametric study was undertaken in which we measured the bandwidth, linearity, and sensitivity of our device as a function of various sensor material properties and optical architectures, as well as under simulated (yet quantifiable) industrial conditions. To quantify the sensitivity of the detector, an interferometric apparatus was set up with a calibrated phase signal introduced by an electro-optic (EO) modulator in one of the legs. To simulate different amplitudes of ultrasonic surface displacements, the detector output was monitored as a function of the EO drive voltage, at a fixed-drive frequency. The data show a high degree of linearity in the displacement range of interest for many commercial applications.