Page 56 - 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

100

80

Signal (%) 60

40

20

0
0 50 100 150
Time (ns)
Figure 2.9 Pulse shape of KrF excimer laser operating at 248 nm and
650 mJ energy.

The excitation of the excimer is achieved by a short pulse. The
resulting laser output is a pulse that starts after the laser threshold is
exceeded and that then rapidly rises to its maximum intensity. A sec-
ond and third maxima can be observed until finally all inversion is
extracted within a few roundtrips in the resonator.
The typical output pulse of the 248-nm excimer laser is shown in
Fig. 2.9 with a full-width, half-maximum (FWHM) pulse length of
22 ns. The pulse is modulated, and in this case, two peaks are seen.
The separation between the peaks is 9 ns, which corresponds to the
resonator length.

2.3 Excimer Laser Designed to Application
The development of excimer laser technology has been driven by sev-
eral main applications. Each application poses different requirements
on the laser to enable successful implementation in scientific, medical,
and industrial fields.

2.3.1 High-Power Excimer Laser
High laser power in the UV region is the domain for the excimer, and
the demand for higher power has driven the development of the exci-
mer laser for many years. Several projects in the 1980s to reach multi-
kilowatt output from the excimer laser were followed globally.
5
Although some interest in the target applications, such as isotope
separation, has faded, the achievements of these basic developments
are still utilized in the mature industrial excimer lasers of today. Typ-
ical output of 600 W is commercially available and proven in indus-
trial operation. Development roadmaps show power levels of more