CO2 lasers, explained by RP Photonics Encyclopedia; carbon ...
CO 2 lasers typically emit at a wavelength of 10.6 μm, but there are dozens of other laser lines in the region of 9–11 μm (particularly at 9.6 μm). This is because two different vibrational states of the CO 2 molecules can be used as the lower level, and for each vibrational state, there is a substantial number of rotational states, leading to many sub-levels.