Enhancement mechanism and optimization analysis of resonant excitation Laser-induced Breakdown Spectroscopy (LIBS-RE) in gaseous ammonia element detection.

The existing techniques for gas components detection, such as Tunable Diode Laser Absorption Spectroscopy (TDLAS) and Cavity Ring-Down Spectroscopy (CRDS), are constrained by their inability to discern the elemental composition of the gas molecules. As a supplementary technology for detecting the total amount of atoms of each component in a gas, Laser-Induced Breakdown Spectroscopy (LIBS) offers significant advantages in gas elemental composition detection. Nevertheless, there are still some challenges to be overcome, including weak spectral signals and instability. In a previous study, we proposed a novel approach for detecting gaseous ammonia molecules using LIBS. The experiment employs a wavelength-tunable, continuous wave (CW) CO laser resonant excitation LIBS (LIBS-RE) to improve signal intensity. A comprehensive examination of the experimental parameters still needs to be required. This paper optimizes the gas flow rate and the energy of the resonant excitation source by comparing the spectral intensities of analysis lines between LIBS and LIBS-RE. The enhancement mechanism of LIBS-RE is analyzed concerning ammonia characteristics, molecular motion, and absorption efficiency. Furthermore, we examined the temporal evolution of H and N ions and atoms. By comparing the spectra of LIBS and LIBS-RE, the maximum enhancement factor for H and N was determined to be approximately 6.59 ± 0.51 and 2.44 ± 0.12, respectively. Finally, the feasibility of using LIBS-RE for the detection of gaseous ammonia has been preliminarily verified. The results demonstrate that LIBS-RE can realize the detection of the atomic content of gas components and has the potential to improve the detection capability.