Page 37 - High Power Laser Handbook

10 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 11

Figure 1.5 Typical low-power diffusion-cooled laser: The fans on top provide
the air cooling. The RF generator is integrated in the housing, and electrical
control interfaces enable the laser power and pulse frequency to be
controlled. 16

Sealed-Off Low-Power Lasers
Diffusion-cooled lasers below the 1-kW power level are usually
sealed-off lasers, meaning that the laser active gas is filled into the
laser cavity once in the factory and is not replaced at regular inter-
vals at the customer’s location. The typical lifespan of the laser gas
fill is about 30,000 hours. To achieve such a long laser gas lifespan,
special care is required when preparing the materials that come in
contact with the laser gas and when determining the leak rates of
the vacuum system (as discussed in Sec. 1.3). Models with power
levels less than 300 W are air cooled and do not require chilled
water. The discharge is powered by an rf-generator that is inte-
grated in the laser head (Fig. 1.5). The excitation frequency ranges
from 40 to 80 MHz.
Due to their compact design, sealed-off lasers can easily be inte-
grated into production lines for marking and coding systems, which
are two of the major applications for these lasers. Other applications
include cutting very thin sheet metal and metal foils or cutting non-
metals, such as plastics, fabrics, ceramics, and wood.

High-Power Diffusion-Cooled Lasers
Diffusion-cooled lasers above the 1-kW power level usually operate
in a near sealed-off mode, meaning that the laser active gas is replaced
in regular intervals at the customer’s location. The typical gas
exchange cycle is 72 hours. The gas is supplied in a small bottle
attached to the laser. To maximize heat extraction from the gas vol-
ume, geometries that have a large ratio of surface area to gas volume
are chosen. The most popular designs are slab and coaxial geometries
(Fig. 1.6).