The Purpose of the Mirrors at the Ends of a Helium-Neon

Multiple Choice

The purpose of the mirrors at the ends of a helium-neon laser is:

A) to assure that no laser light leaks out
B) to increase the number of stimulated emissions
C) to absorb some of the photons
D) to keep the light used for pumping inside the laser
E) to double the effective length of the laser