| Abstract: | The effect of the matrix temperature on laser-induced plasma generated in bulk water by using a
532nm pulsed laser beam has been studied. Ca I and II emission line intensities were recorded
for an aqueous solution of CaCl 2 in the temperature range of 7 °C–70 °C. The emission line
intensities did not follow the matrix temperature in our experiments. Maximum intensities were
observed at ～18 °C for both lines. Herein, a possible mechanism responsible for the observed
variation in intensity is suggested, in which laser-produced bubbles play important roles. Bubble
formation is essential to ignite plasma in the liquid and more feasible at the higher liquid
temperature. However, the abundant bubbles at the higher temperature can scatter the incident
laser beam more effectively to decrease the energy delivered for the laser-induced plasma. Thus,
these two roles have effects on the optical emission intensities in opposite ways. The validity of
the suggested mechanism is discussed based on the plasma temperature, temperature dependence
of the refractive index of water, plasma electron density, scattered light intensity, and plasma
ignition threshold energy. Our result indicates that the temperature of the liquid is also an
important parameter to be considered in the laser-induced breakdown spectroscopy analysis of
bulk liquid samples and its application in deep-sea exploration. |
