Page 57 - High Power Laser Handbook

28 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 Excimer Lasers 29

Laser control

Solid-state pulser

Laser tube

Gas cleaning
Power supply
Gas system
Figure 2.10 High-power industrial excimer laser.

than 1 kW are needed to achieve shorter takt times and high through-
put for industrial applications.
As an example of a high-power industrial excimer laser, Fig. 2.10
shows an excimer laser from Coherent Inc. configured for 600-Hz
operation. All laser modules are integrated into one laser chassis,
which provides all utilities of gas, water, air flow, and electrical sup-
plies and which serves as the laser tube’s stable optical base. The
center part of the excimer laser is the discharge unit, which com-
prises the laser tube, including the gas, and the discharge circuit. The
laser uses solid-state switching in combination with magnetic pulse
compression and voltage transformation, which eliminates routine
maintenance of the excitation circuit. Maintenance costs are further
reduced by an integral mechanical device that enables exchange of
the laser tube without the pulser. High throughput (600-W power)
and high stability (<0.5% root mean square), combined with long
component lifetimes and a single discharge chamber configuration,
significantly reduce operating costs.
For integration into the specific equipment and factory environ-
ment, laser control becomes more and more important. An inte-
grated computer control with customized laser control boards and
a real-time operating system manages all laser parameters on a
shot-to-shot basis and actively stabilizes the energy, the time delay
of the pulse, and other vital laser parameters. In addition, the con-
troller provides fully automated data logging. Communication with
the factory host via Ethernet protocol enables full integration into
the manufacturing process.
The laser’s peak-to-peak energy stability is shown in Fig. 2.11;
the histogram is based on a test run of more than 62 million laser
pulses. More than 99.999 percent of laser pulses are within the target
energy window of ±1.5 percent. This stability is maintained under