Fluorescence of a laser vs its pulse duration

[TheSearch]

When working with a pulsed laser (nitrogen),
How can the fluorescence lifetime be longer than the pulse of the laser?

Thanks for any explanations

 

[DaveE]

The upper-state lifetime is always longer than the pulse in pulsed lasers. This allows you to store energy in the gain medium prior to lasing. In a laser you must be able to create a population inversion, where a photon interaction (of the correct type) is more likely to stimulate emission than be absorbed. i.e. more energy available in upper to lower state transition than vice-versa. This requires some "storage time" in the upper state.

The pulse is short because of stimulated emission. The large quantity of photons cause the upper-state to be depleted quickly during lasing. Prior to that the fluorescence (spontaneous emission) happens more slowly at more random times.

https://eng.libretexts.org/Bookshel...on,_Spontaneous_Emission,_Stimulated_Emission