In a Laser

Multiple Choice

In a laser:

A) excited atoms are stimulated to emit photons by radiation external to the laser
B) the transitions for laser emission are directly to the ground state
C) the states which give rise to laser emission are usually very unstable states that decay rapidly
D) the state in which an atom is initially excited is never between two states that are involved in the stimulated emission
E) a minimum of two energy levels are required.