Helium-neon lasers may be little more than glorified neon signs, but there’s just something about that glowing glass tube that makes the whole process of stimulated emission easier to understand.

Helium-neon lasers may be little more than glorified neon signs, but there’s just something about that glowing glass tube that makes the whole process of stimulated emission easier to understand.

Of course that conclusion was drawn on the basis of comparing these lasers with existing ones. At that time there was the helium–neon laser, which had a very clean spectrum, and the carbon ...