Can Laser Amplification Be Achieved with an External Light Source?

[wasi-uz-zaman]

hi , does input light signal for laser amplification has to be provided by the external source or it is created by lasing material itself?

 

[Gordianus]

Every laser starts from the background signal given by spontaneous emission.

 

[Cthugha]

You can also seed one laser with a different laser as is typical for tunable lasers like Ti:Sapph.