Laser shock wave-induced visible mechanoluminescence from semi-transparent organic crystals.

Indirect focusing of the output from a pulsed infrared Nd :YAG laser through a shock-generating layer onto organic crystals results in the emission of an intense microsecond duration pulse of mechanoluminescence (ML). The ML appears after a threshold laser fluence has been reached and increases sharply above this threshold. This specifies that there is a corresponding amplitude of a laser-induced shock wave that is necessary to induce crystal fracturing. Thus, the intensity of ML can be controlled by varying the laser fluence. Piezoelectric charges produced on the surfaces of a fractured crystal create the foundation for luminescence. Initially, the ML intensity increases with the shock wave pressure and time due to the creation of more surfaces in the crystal; the ML intensity reaches a peak value and then decreases over time. Thus, laser shock wave-induced ML provides a new optical technique for the study of materials under high pressure. Expressions explored for the characteristics of laser shock wave-induced ML satisfactorily explain the experimental results. Copyright © 2016 John Wiley & Sons, Ltd.