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 10.6μm. 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.