The carbon dioxide laser was first used in 1964 with a wavelength of 10.6 μm. Because this is a very efficient laser, with a conversion efficiency of 10% as a commercial model, CO2 lasers are widely used for laser cutting, welding, drilling and surface treatment. As a commercial application laser up to 45 kW, this is the most powerful material processing laser available.
1.Operating Principle
A carbon dioxide laser is a molecular laser. The main substance is carbon dioxide molecules. It can manifest various energy states depending on its vibration and rotation patterns. The basic energy network is shown in Figure 1. The gas mixture in carbon dioxide is a plasma (plasma) formed from a low pressure gas (usually 30-50 Torr) due to the release of electrons. As the Maxwell-Boltzmann distribution law states, in a plasma, molecules exhibit a variety of excited states. Some will exhibit a high energy state (00o1) which behaves as an asymmetrically oscillating state.The molecule also occasionally loses energy when colliding with a hollow wall or emanating naturally. By naturally emitting this high-energy state drops to a symmetrical wiggling state (10o0) and emits photons (a beam of 10.6 μm wavelength) that may travel in any direction.
Occasionally, one of these photons will travel down the cavity along the optical axis and will also wiggle in the resonance mirror.
In general, the working substance of CO2 lasers is a mixture of carbon dioxide, helium, and nitrogen. Nitrogen acts as a buffer gas and its molecules resonate to deliver stimulating energy to carbon dioxide molecules. Since the relaxation level (01110) is the bottleneck, the helium acts as a thermal gullet to transfer energy to the level (01110) to the helium atoms.
2.The Types Of Carbon Dioxide Lasers
The way waste heat is rejected has a large impact on laser system design. In principle, there are two possible ways. The first method is based on the automatic processing of naturally diffusing hot gas to the pipe wall, and the operating principle is the sealing and slow axial flow laser. The second is based on gas forced convection, which operates on the principle of fast axial flow laser. In general, there are five main types of CO2 lasers:
- Sealed or flowless
- slow axial flow
- Fast axial flow
- fast lateral flow
- Laterally Excited Atmosphere (TEA)
Sealed or flowless CO2 lasers are often used for beam deflection laser marking. Its discharge tube is completely sealed. The quality of this laser beam is very good. And in most cases the entire discharge tube can be replaced with a new one and the old one can be refilled so it is easy to maintain. This eliminates the need for a separate gas supply system. Only need to make fewer connections at the laser head. So it’s both tight and lightweight. But its energy output is low (usually less than 200 watts).
TEA CO2 lasers are commonly used in shield fabrication. Operate only in pulsed situations. Air flow is low and air pressure is high. The excitation voltage is about 10,000 volts. This laser beam energy distribution is uniform over a relatively large area. Its highest energy can reach up to 1012 watts and its pulse width is very small. However, this form of laser is difficult to focus on small spots due to multi-state operation.
3.The Power Supply Of The Pump
For CW CO2 lasers, there are generally three main ways to power the pump. For example: direct current (DC), high frequency (HF), radio frequency (RF). The DC power supply is the easiest to design. Electrons alternate between frequencies of 20-50 kHz in high frequency powered mode. High-frequency power supplies are compact in size and more efficient than direct current. In RF power supply electrons alternate between frequencies of 2 to 100 MHz. Compared with direct current, its voltage and efficiency are lower.