What is the mechanism by which CO2 lasers are generated?

The generation of CO2 lasers is primarily achieved through the mechanism of electrical current passing through a mixture of gases, specifically carbon dioxide, nitrogen, and helium. This process, known as gas excitation, involves applying a high-voltage electrical current which energizes the gas molecules. As the gas molecules absorb energy, they enter an excited state and subsequently release this energy in the form of laser light.

In a CO2 laser, the nitrogen molecules are particularly important because they transfer their energy to the CO2 molecules, which have a longer wavelength and thus emit more industrially useful laser light. The presence of helium helps to remove excess heat from the system and aids in the energy transfer process. This gas mixture creates an efficient lasing medium that is capable of producing high-power output and is commonly used in various applications such as materials processing, cutting, and laser surgery.

While other mechanisms such as optical pumping, solid-state crystal excitation, and diode activation are effective in different types of lasers, they do not pertain to the operation of CO2 lasers. Thus, understanding the electrical current through a gas mixture as the correct answer highlights the unique characteristics and operational principles specifically associated with CO2 lasers.