Carbon dioxide (CO2) lasers use the energy difference between vibrational and rotational states of CO2 molecules to emit a long infrared (IR) between 9 and 11µm wavelengths. CO2 lasers are able to maintain a consecutive high level of power and are also some of the most versatile lasers for processing applications. The active medium in a carbon dioxide (CO2) lasers consists of a mixture of carbon dioxide (9.5%), nitrogen (13.5), and helium (77%).
With carbon dioxide lasers, the energy is first absorbed by the nitrogen, which serves as an primer for the carbon dioxide. The carbon dioxide then produces the laser light while the nitrogen continues to pump the CO2 to emit more light. The helium in carbon dioxide lasers has two roles: helping the CO2 return to the ground state and, fostering the heat transfer.
Types of CO2 Lasers
There are three types of carbon dioxide lasers: axial gas-flow, transverse gas-flow, and sealed tube. Axial gas-flow carbon dioxide lasers pump the gas mixture (CO2, N2, and He) into one end of a tube and out the other. Fresh carbon dioxide is pumped in continuously to maintain a flow. Nitrogen and helium are added into the mixture as a way to boost efficiency. The power output for axial gas-flow lasers is typically 40 to 80W per meter of tube length (more or less independent of tube diameter). Folded optical systems can be used as a way to reduce the physical length of the CO2 laser.
Transverse gas-flow lasers are carbon dioxide lasers that have a horizontal gas flow which, rather than flowing downward, which provides high power ratings for continuous CO2 laser operation. When using a transverse excited atmospheric design (TEA), there may be power outputs of up to 10 kW per meter. These carbon dioxide lasers are able to attain an increased power output due to the higher pressure in the tube.
Sealed tube carbon dioxide (CO2) lasers are similar to sealed He/Ne (helium and neon) and Ar/Kr (argon and krypton) lasers in that the gas is preserved within the tube cylinder and is not refilled during use. However, the size of the tube and its bore are different as they are meant to function in using a much longer CO2 wavelength. Sealed CO2 lasers can reach a power output ranging from a few watts to upwards to 100 W or more.
Energy Input Configurations
Carbon dioxide lasers are attainable in two energy input configurations; those with an internal power supply, and those with a reliance on external power for stimulation. In addition, these lasers are designed to output energy as a continuous wave or pulse. Some carbon dioxide lasers are Q-switchable, allowing the device to rapidly change the Q of an optical resonator. This feature is used in the optical resonator of the CO2 laser to prevent a lasing action until an optical gain and energy storage is achieved. When the switch increases the Q of the cavity, pulsing is generated.
Carbon Dioxide Laser Application
Carbon dioxide lasers are found in a wide range of industries and applications. CO2 laser cutters and CO2 engravers are used in marking and laser welding applications. Medical CO2 lasers are also available, their most notable application being skin treatment. Other applications include heat treating, the processing of cardboard, ceramics, composites, fabric, metals, paper, plastics, wood, and many other materials.
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