Describe the construction and working of carbon dioxide laser.

Construction and Working:

The most fundamental form of a CO₂ laser comprise a gas discharge (along with a mix close to which specified above) along with a total reflector at one end, and an output coupler (generally a semi-reflective coated zinc selenide mirror) at the output ending. The output coupler reflectivity is usually around 5 to 15 percent. The laser output may also be edge-coupled into higher power systems to decrease optical heating difficulties. The carbon dioxide (CO₂) laser gas mixture consists of 70 percent He, 15 percent CO₂, and 15 percent N₂.

The rotational and vibrational modes of the CO₂ cannot be excited themselves with photons. While a voltage is placed across the gas, electrons collide along with the N₂ molecules and excite them to their lowest vibrational levels. All vibrational levels occur to be at energy very close to the energy of the asymmetric vibrational states into the CO₂ molecule. Currently, the excited N₂ molecules populate the asymmetric vibrational states within the CO₂ molecule by collisions. The infrared output of the laser is the consequence of transitions among rotational states of the CO₂ molecule of the first asymmetric vibrational mode (001) to rotational states of both the initial symmetric stretch mode (100) and second bending mode (020). Such transitions are demonstrated in the Energy level diagram below:

Construction and working of carbon dioxide laser

In words of Hollas, the emitted photons like a result of these transitions happen at 10.6µm and 9.6µm, correspondingly. The (100) first and second (020) vibrational levels depopulate to lower vibrational levels. Once more, through collisions, the carbon dioxide molecule transfers energy through these lower vibrational levels to the He atoms and the carbon dioxide (CO₂) return to ground state.