Fiber Bragg Grating Sensing System for Detection of Laser-Induced Ultrasonics in Application to Railway

Abstract

This paper presents a new approach for detecting ultrasonic generated by a laser in the confined ablation regime, utilizing an adaptive fiber Bragg gratin (FBG) sensing system. A nanosecond pulsed laser is used for generating ultrasonic wave in aluminum specimen with water-confined layer. Experimental measurements demonstrate that the amplitudes of Rayleigh wave in the confined ablation regime are unexpectedly 8 times larger than the ones in direct ablation regime when the incident laser intensity is about 0.12×109 W/cm2. It is shown that confinement of the surface with a waterconfined layer provides an effective method of enhancing amplitude of laser-induced ultrasonic waves in the target material about an order of magnitude. These results indicate that the possibility of applying the laser-based FBG ultrasonic sensing system in nondestructive testing (NDT) and structure health monitoring (SHM) within special structural materials of high-speed train