A Situation Known as "Population Inversion" Is Needed for Lasing

question 43

Multiple Choice

A situation known as "population inversion" is needed for lasing action.What does "population inversion" mean?

• A) Electrons are in the -1/2 state.
• B) Excited atoms must be at the top of the laser tube.
• C) Excited atoms must be at the bottom of the laser tube.
• D) The number of excited states that are to emit photons are in greater number than the lower states at which the transition is ending.
• E) The number of lower states are in greater number than the upper states participating in the lasing action.