Question

c) (1 pt) If you set up all the parts for a laser and then just barely turn on the pump that puts atoms into the excited state nothing very interesting happens. As you gradually increase the pumping you still do not get any laser light out. However, once you reach a certain point (called the “threshold") suddenly laser light comes out and as you increase above that the amount of laser light produced increases rapidly. This behavior can be observed in the PhET laser applet as well as in any real laser. Explain this behavior of a threshold for laser operation in terms of the underlying physics of lasers.

Answer 1

When we simply operate the pump , nothing interesting happens until one staged is reached while increasing the pumping, when suddenly the amount of laser light produce increases manifolds.

It happens due to the following reasons:

The primary conditions for a laser to work are :

a) atleast one meta stable state

b) population inversion in any higher level as compared to the lover level

So, basically when we keep on increasing the pumping, the population inversion takes place which means that the population density of carriers are increased in one of the excited levels as compared to a lower energy level and hence this population inversion stage is used to stimulate the carriers for a de-excitement and hence the laser action is produced. This cannot be achieved until a stage of population inversion is achieved.

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