Study on the most influential parameters in low-power laser generated ultrasound

Abstract

The current work studies the influence of the most widely used time-domain techniques for signal to noise ratio (SNR) increase for laser-generated ultrasound (US), employing a low power (150 mW) modulable diode: these methods utilize highly random pseudo-noise (PN) sequences which, after the use of the cross-correlation, underline the presence of an ultrasonic output. PN sequences can broaden the signal's band through random lengths of LOW and HIGH levels in laser pulses' duration, scattering the energy on a wide range of frequencies: this might represent a disadvantage in case of controls with narrow-band probe, which are the most used instruments for this kind of applications. From this point of view, creation of specific drive signals allows to improve significantly the control on frequency response. A SNR consistent with the ones achievable through the classically adopted methods is highlighted, but featuring an advantageous concentration in the output frequency band.