Common gas lasers?

Question

Why don't Neon lasers or helium lasers exist on their own, and instead they are combined to form He-Ne lasers?

Answer 1

The metastable state that makes the laser work is the Neon 3s2 state. Direct excitement alone won't produce the required population inversion in Ne. However, Helium has couple of long-lived states that don't lase, but because of a coincidence of energy levels between He and Ne, excited He atoms can collide with Ne atoms and excite them into their metastable state.

See the reference below for all the details.