Stabilization of laser-induced plasma in bulk water using large focusing angle

Laser focusing geometry effects on plasma emissions in bulk water were investigated with five focusing angles ranging from 11.9° to 35.4°. Fast imaging and space-resolved spectroscopy techniques were used to observe the plasma emission distributions and fluctuations. We demonstrated that by increasing the focusing angle, discrete and irregular plasma formed in multiple sites could be turned into continuous and stable plasma with single core fixed at the laser focal point. This indicates the key role of laser focusing angle in the stabilization of plasma positions, which is crucial to the improvement of laser-induced breakdown spectroscopy repeatability in bulk water.