Carbondioxide is a four level molecular laser. The CO2 molecules consist of two oxygen atoms and a carbon atom between them. These molecules undergo three different types of vibrational oscillations. These three vibrational configurations are called vibrational modes.
The three vibrational modes are:
i) Symmetric stretching mode: In this mode, the oxygen atoms oscillate along the axis of the molecule simultaneously departing or approaching the carbon atom which is stationary.
ii) Asymmetric stretching mode: In this mode, all the three atoms oscillate but oxygen atoms move in one direction and carbon atom moves in the opposite direction.
iii) Bending mode: In bending mode, atoms move perpendicular to the molecular axis.
As a result of vibrational modes, CO2 molecule is characterized not only by electronic levels but also by vibrational and rotational levels. Each electronic level is split into various vibrational sublevels and each vibrational level is further splitted into rotational sublevels. The energy difference between various electronic levels corresponds to visible and ultraviolet region. The energy difference between various vibrational levels corresponds to the infrared region while the energy difference between various rotational levels corresponds to far infrared region of the spectrum.
Note: In next article, I will explain the construction and working of CO2 laser. Till then, try to make the modes diagram. In case of any problem in this article or any other physics article, post in the comment section.
Reference: This article is referred from my authored book “optics and lasers” having ISBN 978-81-272-2948-2