Enhancement of femtosecond laser-induced plasma fluorescence using a nanosecond laser.

We demonstrate the enhancement of femtosecond (fs) laser-induced filaments in air and nitrogen flow fields using a nanosecond (ns) laser. With the ns laser being imposed on the filaments, the length and the emission intensity of the filaments were largely increased. Temporally resolved spectra of the enhanced filaments were obtained. The results show that the ns laser enhanced the short-lifetime fluorescence of nitrogen, which comes from the transition processes of N2 + (B2 Σu + - X2 Σg + ), N2 (B3 Пg - A3 Σu + ) and N2 (C3 Пu - B3 Пg ). However, it had little effect on the long-lifetime chemiluminescence, which mainly comes from reactions such as N2 (A3 Σu + ) + N2 (A3 Σu + ) → N2 (X1 Σg + , v = 0) + N2 (B3 Пg ). A possible explanation of this phenomenon is given, and this phenomenon might have potential applications in instantaneous one-dimensional measurements of various species in gas flow fields.