The physical design of a CO2 laser consists of a gas filled tube sand wedged between a pair of mirrors, this tube is excited by a RF or DC electrical discharge. Contrary to popular belief CO2 is not the only gas apparent inside these tubes. The gas composition of a typical CO2 tube is a mixture of:
77% He (Helium) 13.5% N2 (Nitrogen) 9.5% CO2 (Carbon Dioxide).
Why is my tube branded as CO2 and not a Helium tube?..
Well, the sealed CO2 Tube requires the gas to flow or a pumping mechanism, this is achieved by exciting the nitrogen molecules through electrical discharge. This causes the N2 to collide with the CO2 molecules.
Types of CO2 Lasers
- Axial gas flow: Gas is physically pumped in one end and out the other of the tube, this fresh gas replaces the depleted CO2. He & N2 are commonly added to increase efficiency. Typical power outputs of 40-80w per meter for this tube.
- Transverse gas flow: Gas flows across the tube as apposed to down the length of the tube, this ensure a fresh mixture along the entire length of the tube. Typical power outputs of 10kW per meter can be achieved with this type of arrangement.
- Sealed tube: Similar to sealed HeNe lasers but with dimensions tuned to CO2 excitation wavelength. Typical power outputs of 1-160W are typical of the type of tube.
DC & RF Excitation
Most if not all China import lasers feature a sealed tube design and are DC excited, power control is achieved with pulse width modulation and not current control on this type of laser. Power to the tube is pulsed (pwm) the duty cycle of this pulse (time on vs off) dictate the RMS power (root mean square). Due to the nature of a pwm digital signal only an analog current meter can be used to read this signal.