Generating Laser
The above left is a three-level laser energy diagram, where
. Which of following explanations is NOT correct?
a) Level is a metastable state.
b) Electrons stay longer at than at .
c) There is no electron that shows a spontaneous transition from to .
d) If a laser beam can be generated constantly, the electron population in level must be larger than the electron population in level
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A&B) metastable state is a state where electronics spent more time.These are states generated by electron bombardment but not by the natural photo excitation
C)actually spontaneous emtion (direct transition of electron from higher state to lower state) exists in LED's but in LASER's radiation occurs by the stimulated emition(electron passes through different levels). here E2 to E1 is single bad transition so,it is a spontaneous emition
D)population inversion (more number of electrons in an excited state than in lower energy states) is the basic principle for laser operation. this can be achieved by constantly pumping the electrons to higher energy level