Research on the fluorescence emission from water vapor induced by femtosecond filamentation in air

Highlights: • Effect of laser energy and humidity on fluorescence emission is investigated. • OH and N₂ fluorescence show different emission behaviors as humidity increases. • Influence of polarization on OH and N₂ fluorescence emission is quite different. Our experiments show that initial energy and humidity strongly influences the water vapor fluorescence induced by ultrashort intense femtosecond laser pulses. It is found that the fluorescence signal can be enhanced by both increasing the humidity in the case of fixed energy and increasing the pulse energy in the case of fixed humidity. In addition, water vapor fluorescence emission in the linear polarization is stronger than that in the circular polarization due to the higher dissociation efficiency of linearly polarized pulses. The mechanism of water vapor fluorescence emission during femtosecond filamentation is discussed based on the analysis of these phenomena.