C02 LASER

C02 laser is a molecular gas laser and infrared emission laser. The emission occurred on the two vibration rotational bands of C02 molecule at wavelength of 10.6 µm in the infrared. It should be equipped with pulsed and continuous wave (CW) modes of operation.

To operate the laser in pulsed-mode, two different techniques have been used. In the first technique, no switching power supply was used. In this simple technique, the discharge impedance collapse caused by high voltage preionizer pulses has been exploited to produce laser pulsation. Using this method the laser has been operated in pulsed-mode up to 1.3 kHz frequency, with 100% amplitude modulation depth and with a peak to average power ratio of 3.35. In second technique, the discharge current has been pulse width modulated using a switched-mode power supply to operation the laser in pulsed-mode up to 1kHz frequency.

There are many different types of design for the CW C02 laser, which generally can be divided into three different groups of slow flow, sealed-off and fast-flow laser system.

Seal off C02 laser
In general, seal-off laser mean discharge gases are completely sealed within the discharge tube. It offers convenient application because there are no vacuum and bottles needed. Heat generated by the electrical discharge is removed by heat conduction through by a water jacket. The output power can be increase only by increasing the discharge tube length. This system is used up to about 100 W.

Slow flow C02 laser
Below is the schematic diagram of a slow flow (diffusion cooled) CW C02 Laser. It is relatively simple to design, build and maintain, and predominate in the range 100 - 400 W power output. The lasing gas is fed from high pressure cylinders into the plasma tubes and flows slowly through them at a few metres per second. The maximum power obtainable from the tube is also dependent on the length of the excited of the plasma tube. Heat generated by the electrical discharge is also removed by heat conduction through by a water jacket. Gas is slowly pumped through the tube in order to refresh the gas mixture continuously.

Fast flow C02 laser
For a fast flow system, the heat absorbed by the C02 gas can be removed by the flowing gas. This technique allows an increase of obtainable power per unit length of discharge by several orders of magnitude. Multi kilowatt electrically excited lasers in reasonable sizes can be built. The fast flow system can be divided into two types, which are fast axial flow and fast transverse flow system.

In the fast axial flow (FAF) C02 laser the gas mixture is forced through the tubes at velocities up to 400 m/s. It is re-circulated through the tubes many times and after each passage through the discharge is cooled directly in a heat exchanger. Roots type gas pumps are usually used in these lasers.
Above is the schematic diagram of a fast axial flow C02 laser, which the optical axes, current and gas flow are in the same direction. The laser's power output is no longer dependent on the length of the discharge tubes. However, largely on the rate of mass flow of gas through them. Laser power therefore be increased either by increasing the volume flow rate or the pressure of the re-circulated gas, provided no other mechanical or electrical limitations. In practice the power output of a FAF C02 laser may be limited by one or more factors as below: