A Brief Analysis on the Working Principles and Categories of the CO2 laser The first usage of CO2 laser was in 1964 with wavelength of 10.6Οm. As it’s a very efficient laser, its conversion efficiency can reach up to 10% as a business model; thus it’s widely used in laser cutting, welding, drilling and surface treatment. As a commercial application laser, it can reach 45 KW as the most powerful material handling laser.
1.Working principles CO2 laser is a kind of excimerlaser, whose main substance is CO2. Its different energy states depend on its vibration and rotation form. For the basic energy network, please refer to Fig 1. The gas mixture in CO2 is formed through electron releasing. As the Maxwell-Boltzmann distribution law says, molecules present a variety of excited states in plasma. Some high-energy states (00o1) molecules present their asymmetric
swing state. When collide with hollow wall or emanate naturally, the molecule will lose energy accidently. Through natural emanation, the high-energy state will fall to symmetrical swing state (10o0), and it can also emit photons (light beam with wavelength of 10.6μm) that can spread to any direction. Fig 1. Simple energy level diagram of CO2 Generally, the working substance of CO2 laser consists of mixture gas composed of CO2, Helium and Nitrogen gas. As buffer gas, Nitrogen gas and its molecule transmitter exciting energy to CO2 resonantly. As the relaxation level (01110) is the bottleneck, Helium is used to transfer energy to helium atom (01110) as the heat sink. 2.Categories of CO2 laser Waste heat rejection plays a very important role in laser system designing. Theoretically, there are two possible ways. The first is based on automatically processing steam for its natural diffusion to pipe-wall. The second is based on air forced convection; its working principle is fast axial flow laser. Basically, there are five CO2 lasers: Sealed type or no flow type Slow axis flow Fast axis flow Fast transverse flow Transverse excitation atmosphere（TEA） Sealed or no flow type CO2 laser is usually used in beam deflection laser for marking. Its discharging tube is completely sealed. It has high quality. It’s easy to maintain, because in most cases the discharging tube can be renewed and reaerated. Thus there is no need to use separated gas. What we need is some connection for the laser head. Thus it’s compact and lightweight but with lower energy output (less than 200W). TEA CO2 laser is usually used in the manufacturing of shield. It operates only by pulse, with low airflow and high air pressure. Its driving voltage is about 10000 V. The energy of this kind of laser beam distributes in relatively laser areas. Its highest energy can reach up to 1012 W with small pulse width. Nevertheless, this type of laser can hardly focus on small point due to its multimode operation.
3.Power supply of pump There are three means of power supply for pumps generally, as for CW CO2 laser; such as direct current (DC), high frequency (HF) and radio frequency (RF). The power supply design of DC is quite simple. Electron alternates around 20-50 KHz in HF power supply. Compared with DC, HF power supply is dense in size and with high efficiency. Electron alternates around 2-100 MHz in RF power supply. Compared with DC, the voltage and efficiency of RF power supply is relatively lower.