Laser-induced breakdown spectroscopy system for remote measurement of salt in a narrow gap

• Remote measurements with 5 m optical path of the chlorine concentration of a salt attached to stainless steel located at the side wall of a narrow gap were performed by using LIBS.
• A compact optical device was developed to access the surface of stainless steel for focusing laser pulses and collecting laser-induced plasma.
• The chlorine concentration from 0 to 100 mg/m2 can be evaluated quantitatively by use of the calibration data of chlorine emission intensity.

We performed remotely measured, with a 5-m optical path, the chlorine concentration of a sea salt attached to stainless steel (SS) located at the side wall of a narrow gap (width ~ 50 mm) by using laser-induced breakdown spectroscopy (LIBS) in two configurations. One uses mirrors for transmitting laser pulses in air, while the other uses multimode fiber. A compact optical device was developed to access the surface of SS for focusing laser pulses and collecting laser-induced plasma. With the configuration in which laser pulses pass through the fiber, the chlorine spectrum could be detected by fiber-coupled LIBS. In addition, with the configuration in which laser pulses pass through air, chlorine concentrations from 0 to 100 mg/m2 could be evaluated quantitatively by using the calibration data of chlorine emission intensity. These results show that the proposed system enables the measurement of chlorine at the surface of SS remotely, instantly, and quantitatively.