Effects of Ambient Temperature on Laser-Induced Plasma in Bulk Water

Laser-induced breakdown spectroscopy (LIBS) has been successfully applied to ocean exploration, but the changes in marine environmental factors could have an important impact on the LIBS signals. The aim of the research is to investigate the ambient water temperature effects on laser-induced plasma in bulk water. Both the spectroscopic and fast imaging techniques are used to observe the plasma emission with the temperatures in the range of 5-60 ℃. It is shown that as the ambient temperature increases, an obviously increasing trend of emission intensity is observed, both for the atomic and ionic lines of Ca. Higher plasma temperature and electron density can be obtained at higher ambient temperature. The image results demonstrate that hotter and larger plasmas can be produced in water with the increase of ambient temperature. In addition, it is found that the changes of plasma emission and morphologies could be related to the changes of physical property parameters of water such as thermal expansivity and viscosity with ambient temperature. The results suggest that the ambient temperature has great influences on laser-induced plasma, which needs to be taken into account in underwater LIBS measurement, especially on-site marine applications.