= Helium-neon laser
A <helium-neon laser> uses an electrical discharge in a <helium>–<neon> gas mixture to establish <optical gain> on neon transitions. Excited helium atoms transfer <energy> in collisions to suitable excited neon states, helping create the required <population inversion>.
A discharge tube and aligned resonator <mirrors> form the apparatus; one <mirror> transmits part of the circulating <light> as output. The familiar red emission is one selected transition rather than a direct photograph of the entire discharge spectrum. Gas pressure, discharge current and <mirror> selection affect oscillation, while misalignment can suppress the <laser> output even when the discharge remains visibly bright.
Back to article page
