Abstract
Laser Induced Breakdown Spectroscopy (LIBS) based spectral and temporal measurements are carried out to identify and rank the Sodium in bulk liquid under high pressure condition. The experiments are carried out by varying the incident laser irradiance (4 to 5 * 1011 W/cm2), ambient pressure condition (1 to 8 atm) and stand-off collection distance (0.6 to 2 m). The concentration of Sodium Chloride (NaCl) in the sample solution is varied between 250 and 1500 ppm. From the spectral data, the Na I emission line (589 nm) is visualized for all experimentation condition. Emission due to singly ionized atom and doubly ionized atom are not observed, due to the requirement of high ionization energies. It is observed that the Na I (589 nm) peak intensity decreases with increase in ambient pressure condition, due to the plasma condensation effect. It is also observed that the Na I (589 nm) peak intensity increases with increase in incident laser irradiance. Temporal measurement based quantification of Sodium in bulk liquid is carried out. It is observed that the plasma emission time period (Na I at 589 nm) increases with increase in NaCl concentration. This is related to the re-excitation of neutral atoms (Na I) in the plasma state. In the stand-off distance analysis, it is observed that the plasma (Na I) emission peak intensity and time period of emission decreases with increase in stand-off collection distance. This might be due to the low coupling of plasma emission to the measurement system, at longer stand-off distances. The Na detection limit of about 10 ppm is achieved for a laser irradiance of 3 * 1011 W/cm2. The above specified detection limit is obtained for an ambient pressure condition of 1 atm and stand-off collection distance of 0.6 m. On a summary, remote LIBS with temporal measurement is highly suitable to identify and rank the Sodium concentration in bulk liquid under high pressure condition. However, the calibration of LIBS measurements at different experimental condition is required to utilize the instrument in real-time environment.
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