Page 39 - High Power Laser Handbook

12 G a s , C h e m i c a l , a n d F r e e - E l e c t r o n L a s e r s Carbon Dioxide Lasers 13

are proportional to the intensity of the focus and not to the power of
the laser beam. Cutting thicker materials is determined by the dynam-
ics of the molten material and the laser’s power, not by the laser’s
intensity.
Because diffusion-cooled lasers have lower efficiency than fast-
flow lasers, the costs for cooling and pumping the gain medium per
unit output power are higher. Since the costs of the other laser compo-
nents are lower as compared with those for fast-flow lasers and because
diffusion-cooled lasers have no moving parts (e.g., the turbo radial
blower), the power level range at which fast-flow designs become more
cost effective than diffusion-cooled lasers is about 3.5 to 4 kW.

1.4.2 Fast-Flow CO Lasers
2
The most common design for industrial CO lasers with power levels
2
above 2 kW is the fast axial flow laser. This laser has been the work-
horse of the industry and has revolutionized sheet metal processing.
Power levels up to 20 kW are available as standard products, and lasers
with up to 100-kW laser power have been built for special projects.
The rf power in fast-flow lasers is delivered to the gas discharge
through electrodes that are attached to quartz tubes in which the dis-
charge runs. To keep the laser gas cool enough to maintain efficient
laser operation, the gas is removed from the discharge area, cooled in
heat exchangers, and returned to the discharge area by a radial turbine
blower (Fig. 1.8). Before the laser gas reenters the discharge area, the
compression heat generated by the radial turbine blower is removed
in a heat exchanger. The laser power scales with the amount of heat
&
that can be removed from the laser gas (gas volume flow V) and the

Radial turbine blower

Cooling coil

Bending
mirror

Rear mirror
Output mirror
Discharge path
Electrodes
Outgoing laser beam

20
Figure 1.8 Multikilowatt fast-flow laser. (Source: TRUMPF )