Simultaneous measurement of film thickness and concentration of urea-water solution by laser spectroscopy

Measurement of film thickness and concentration of urea-water solution is very important in many practical applications. However, these two important parameters can only be determined separately by conventional measurement methods. Here, a novel online measurement method by laser spectroscopy was developed to obtain the film thickness and concentration of urea-water solution simultaneously. By sensitivity analysis and cross-validation, an optimal wavelength pair (7040.75 cm −1 and 6761.00 cm −1 ) was chosen to determine film thickness and concentration. As shown from cross-validation, uncertainties of the developed method were smaller than 1.40% for thickness measurement and 5.76% for concentration measurement.