Nondestructive Evaluation of Concrete Structures by Laser Ultrasonic Method

The nondestructive testing of concrete structures has been attempted using ultrasonic methods such as impact echo methods, though no automated remote testing method has been realized yet. The laser ultrasonic method is a non-contact nondestructive evaluation method that uses short laser pulses to generate and Continuous Wave (CW) laser radiation to detect ultrasonic waves. In the applications of ultrasonic to nondestructive testing, it is necessary to choice the characteristics of the ultrasonic field radiated by the ultrasonic transmitter. The characteristics of that exited by laser pulses determine the usefulness in detecting flaws. In this paper, we present experimental results of investigation of relation between the waveforms of the ultrasonic exited by Q-switched pulse laser and the wavelengths of the pulse laser in concrete. The experiment was carried out using the Q-switched pulse laser of several wavelengths. We clarify that it is possible to control the amplitude and the pulse width of P-wave by a choice of the pulse energy and the wavelength of the laser source respectively.