My Dear Mr. Haddawi

The same traditional methods are used to measure the life time of the upper laser level and one important parameters is effect in the life time is temp.

with best Regard

Jassim

Dear s.F. Haddawi ;

I think you will find a good solution in the link bellow:

https://www.newport.com/medias/sys_master/images/images/hbc/h43/8797050241054/AN33-Estimating-Laser-Diode-Lifetimes-and-Activation-Energy.pdf

Regards;

I think, if you view its optical spectrum in a steady state operation, and then calculates its resonator finesse, you wil get its photon liftime

Article Random laser properties of Nd crystal powders

Following.