Page 56 - Tunable Lasers Handbook

3 Tunable Excimer Lasers 37

I\ Other excited states

>
P
t
o
a, \ r = AB’ * Excimer upper level m i c
c
w
Excirner emission excitation
A+B
Weak Van Der Waals Bonding

Internuclear Separation
FIGURE 1 Energy level diagram for excimer lasers showing relevant electronic states.

the pumping rate and the plasma conditions. Predicting the lasing spectra, or even
fluorescence. can involve more than 100 kinetic reactions and loss processes.
The most developed of this class of molecules as laser media are the rare
gas halides, which show strong lasing on the B+X transitions of ArF (193 nm).
KrF (248 nm), XeCl(308 nm), and XeF (351 and 353 nm). The C+A transition
of XeF (490 nm) has also emerged as a potential high-power tunable laser
source in the visible spectrum.
The rare gas excimers are important sources of WV radiation: Ar, (126
nm), Krz (146 nm), and Xe, (172 nm). The requirement that the pump source be
a relativistic electron beam has limited their availability and development.

2.1 Rare Gas Halide Excirners
The most developed of the excimer lasers are the rare gas halides, which
have shown high single pulse energy, high average power, and high efficiency.
The most important of these are ArF, KrF, XeC1, and XeF. The former two, with
an unbound ground state, exhibit continuous homogeneously broadened spectra.
The latter two excimers, with weakly bound ground states, exhibit the highly
structured spectra of overlapping rovibrational transitions.

2.1. I ArF (793 nm)
The ArF spectrum is a continuum similar to that of KrF. The B+X emission
is a *x-?X transition. The reaction kinetics are also similar to KrF. However,