Laser-induced breakdown spectroscopy for the measurement of air humidity using spectral line intensity ratio

Laser-induced breakdown spectroscopy (LIBS) is widely used in air environment. Humidity is an important parameter in the air environment, and its variation can affect the accuracy of LIBS. Therefore, measurement of humidity is very necessary when performing LIBS applications. We present a method for humidity measurement using laser-induced breakdown spectroscopy. The intensity ratio between spectral lines was used to establish the relationship with relative humidity. The relative humidity has a linear relationship with the intensity ratio of Hα 656.3 nm to N II 463.0 nm, N II 500.5 nm, N I 746.8 nm and O I 777.4 nm. The linearity can exceed 99.9%. The linear relationship was also used to measure the air humidity, and the measurement results were accurate. This study confirms the feasibility of using laser-induced breakdown spectroscopy to measure humidity. The advantage of this method is that when using LIBS applications, no other instruments are required to measure humidity.