As we know, if we have a group of atoms at a moment N(t) in an exited state, it will exponentially decrease according to the relation:(adsbygoogle = window.adsbygoogle || []).push({});

N(t)=N(0) exp(-At)=N(0) exp(-t/(tau))

Where A is the Einsteins constant for the spontaneos emission,

In my book they defined tau in the relation I explained in PDF

Can Any one tell me WHERE DID HE BROUGHT THE SECOND RELATION FROM????

Thanks for reading

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Life time in spontaneous emission for laser

**Physics Forums | Science Articles, Homework Help, Discussion**