What Is Negative Absorption Coefficient in Lasers?

[Rahul Manavalan]

The fact that energy in a laser can propagate without much loss over long distances is quite shocking !
It's a renowned fact that energy is dissipated when propagation takes place through any medium...
(I'm fully aware that laser is an exception)
But I have quite a difficult time understanding the concept of negative absorption.
Is laser the only device that works on the principle or are there more?.??

 

[Bystander]

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