Q. Assertion: In He-Ne laser, population inversion takes place between energy levels of neon atoms. Reason: Helium atoms have a meta-stable energy level.
VMMC MedicalVMMC Medical 2005
Solution:
The transition in He-Ne laser is shown below.
An electric discharge in the gas pumps the helium atoms to higher energy states (which is metastable state $ \approx {{10}^{-8}}\,\sec $ ) These He atoms collide with the ground state neon atoms and excite to higher states (levels) and produce an inverted population inversion causing a unidirectional photon beam (laser light).
