Energy transfer in laser-induced plasma generation on nano-aerosols

We report on the investigation of laser-induced plasma generation mechanisms in laser-aerosols interaction with dry Cu nano-aerosols of different sizes as the samples. The energy transfer mechanism is firstly analyzed based on the comparison of electron temperature between pure air and that containing aerosols, and the breakdown energy threshold for particles with respect to aerosol density. It is inferred that both laser-particle interaction and plasma-particle interaction exist in laser-induced plasma generation in nano-aerosols. The plasma-particle interaction becomes dominant for the cases with low aerosol density. Specifically, the plasma plays dual roles in interaction with aerosols-atomization and excitation. According to the electron temperature drop for the case with aerosols compared with pure air, we roughly estimated the energy loss of plasma and found that it is not enough to fully atomize the particles. On this basis, the smaller particles, which can absorb more energy because of the larger relative surface and more absorbing entities presenting in the plasma, are helpful to achieve higher LIBS signal intensity, electron temperature and density. This work is useful in understanding the mechanism of laser-aerosol interaction, which would be of importance in the wide applications of laser-induced plasma generation from aerosols including radiation generation, aerosol detection, and the dual-pulse LIBS technique.