Page 61 - High Power Laser Handbook

32 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 33

Figure 2.14 Compact excimer laser for refractive surgery (LASIK).

tabletop excimer laser, the ExciStar XS from Coherent Inc., is shown
in Fig. 2.14. This compact model measures only 650 × 300 × 410 mm
and easily integrates into medical systems. The laser delivers 5-mJ
pulse energy that is stabilized by a built-in energy monitor and a
feedback-loop with a typical repetition rate of 500 Hz. Long lifetimes
of the gas and components lead to maintenance-free operation of
more than one year.

2.4 Application of High-Power Excimer Lasers
The unique beam properties of today’s excimer lasers allow these
lasers to transform an unspecific material layer into a high-value
functional surface. Representing today’s most cost-effective and
dependable pulsed UV laser technology, excimer lasers enable inno-
vations in diverse growth industries, including the medical, micro-
electronic, flat panel display, automotive, biomedical device, and
alternative energy markets. The combination of two fundamental
aspects—wavelength and peak energy or peak power—determines
the excimer laser’s unique value, adding potential in high-tech indus-
tries that more than ever must balance product size, efficiency, and
performance demands with process speed and production costs.
The unique interaction of pulsed short UV with materials such
as polymer and poly(methyl methacrylate), or PMMA, was studied
9
by Srinivasan as early as the 1980s. The use of a high-intensity
beam with photon energy that is higher than the bond energy of the
substrate material (e.g., 5 eV for 248 nm) allows for the unique abla-
tion mechanism of UV light and excimer lasers. From these studies,
the term cold ablation was generated to describe the removal of poly-
mer material by breaking chemical bonds rather than thermal
decomposition. As the name indicates, there is minimal effect on the
surrounding material due to the strong absorption of the UV laser
radiation. The application of the 193 nm laser for photorefractive
surgery is a direct result of these studies and has driven the devel-
opment of the compact, low-powered excimer laser for the popular
LASIK application.