AlO molecular spectral emission enhanced by delayed double-pulse laser ablation of aluminum target in air.

• the mechanism of molecular emission spectrum enhancement. • femtosecond and nanosecond double-pulse laser ablation. • strengthening signal intensity and improving analysis sensitivity. The spectral emission of molecules is important for determination of some elements or for isotopic analysis. However, laser ablation molecular emission spectroscopy is usually limited by low sensitivity and high detection limits. Here, femtosecond (fs)-nanosecond (ns) double-pulse laser in the orthogonal geometry was performed to ablate the aluminum target in air. As ns laser pulse delayed the fs laser pulse, the AlO B2Σ+-X2Σ+ emission spectral intensity first increased and then weakened. The optimal enhancement of molecular emission occurred during the second ns laser ablation aerosol particles (formed after the fs laser induced plasma extinguished). The evolution of AlO emission with different fs-ns inter-pulse times was discussed, which was related to whether the aluminum plasma induced by the fs laser pulse expanded to the ns laser focus position and whether the plasma was extinguished, before the ns laser pulse excitation. The influence of the number of ablation laser pulses on the molecular spectrum intensity distribution was also studied, which was found to be attributed to crater effect by fs laser ablation. These results are helpful to deeply understand the mechanism of molecular spectral emission enhanced by double-pulse laser ablation. [ABSTRACT FROM AUTHOR]

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