The Cadmium metal is heated to a temperature of 250⁰C, to create the appropriate vapor pressure.
The Cadmium vapor pressure of a few millitorr is added to Helium gas at a pressure of 3-7 millitorr.
Since Helium is a noble gas, its excitation energy is very high (24.46 [eV]) compared to the Cadmium which is a metal with low excitation energy (8.96 [eV]). Thus in He-Ne laser the Helium remains electrically neutral, and fills the cavity of the tube, while the positive Cadmium atoms are moving toward the negative cathode.

In the design of the tube of Helium-Cadmium laser most of the effort is to reduce to a minimum the amount of Cadmium ions on the cathode. The best He-Cd lasers loose about 1 [g] Cadmium metal for 1,000 hours of operation of the laser.

For comparison, the gain and power output of the main two lines of He-Cd laser are higher than for the He-Ne laser, but less than for the Ar⁺ laser.

 Characteristics of He-Cd lasers:

• Output wavelengths: Blue light 0.4416 [mm],  and Ultra-Violet (UV) light 0.3250 [mm].
• Maximum output power: 150 [mW] in the blue line, and 50 [mW] at UV.
• Maximum total efficiency: in the blue line 0.02%, and in the UV 0.01%.
• Spectral width: 0.003 [nm] (about 5 [GHz]), and coherence length: about 10 [cm].
• Distance between two longitudinal modes: about 200 [MHz].