Synchronized delivery of Er:YAG-laser pulses into water studied by a laser beam transmission probe for enhanced endodontic treatment

We examine the effects of the synchronized delivery of multiple Er:YAG-laser pulses during vapor- bubble oscillations into water. For this purpose, we used a laser beam transmission probe that enables monitoring of the bubbleʼs dynamics from a single shot. To overcome the main drawbacks of this technique, we propose and develop an appropriate and robust calibration by simultaneous employment of shadow photography. By using the devel- oped experimental method, we show that the resonance effect is obtained when the second laser pulse is delivered at the end or slightly after the first bubbleʼs collapse. In this case, the resonance effect increases the mechanical energy of the secondary bubbleʼs oscillations and prolongs their duration. The presented laser method for synchronized delivery of Er:YAG-laser pulses during bubble oscillations has great potential for further improvement of laser endodontic treatment, especially upon their safety and efficiency