HIGH POWER LASERS
There are two main types of high power CO2 lasers, slow flow and fast flow. In a slow flow laser, the relatively low flow rate of the gas limits heat conduction through the glass tubes to dielectric oil or water cooling jackets, thereby outputting only about 50-75 watts per meter of cavity length. The fast flow principle relies on high-speed gas transport to aid in heat removal in place of oil cooling jackets. This produces 500-750 watts per meter of cavity length.
A CO2 laser gas mixture is circulated, via a turbine, roots blower or vacuum pump, through an electrode structure, which creates electrical excitation of that mixture. The electrical excitation provides, via molecular collision, pumping of the CO2 molecules which in turn can be stimulated to release optical energy to the laser beam. After the gas mixture passes through the discharge region it must be cooled to remove non-useable thermal energy. This cooling is achieved by passing the gas through gas-to-water heat exchanges while it is continuously recycled.
Situated on both ends of the discharge region are optical assemblies, which are held in a fixed position by a water-cooled resonator assembly. The mirrors mounted in these assemblies form an optical resonator, which reflects light back and forth through the discharge region with accompanying amplification on each pass. A portion of this circulating optical power is allowed to exit through an output mirror. This optical output is controlled either by electronic on-off shuttering of the discharge or absorbing the output with a water cooled shutter mechanism situated between the output mirror and output aperture of the cabinet.
In order to measure the output power of the laser, a small portion of the circulating resonator power is allowed to leak through the rear mirror onto a power meter. The output power is proportional to this rear mirror leakage. The laser beam is then directed by mirrors, through the focussing lens, to the work-piece.