6.1.1 Helium-Neon (He-Ne) Laser

The Helium-Neon laser was the most common laser until the spread of diode lasers in the last few years. It was first built in 1961 by Ali Javan. The active medium is a noble gas Neon (Ne), and it is a 4 level laser.

The energy level diagram of a Helium-Neon laser is described in figure 6.1.

Two meta-stable energy levels act as upper laser levels. The He-Ne laser have two lower laser levels, so quite a few wavelengths can come out of the transitions between these levels.

The important wavelengths are:

l₁=0.6328 [mm] (632.8 [nm]),  l₂=1.152 [mm], l₃=3.3913 [mm], l₂=0.5435 [mm]

Figure 6.1: Energy Level Diagram of He-Ne Laser