10'8'2 Excitation of Rare GasHalogen Excimer Lasers

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10.8.2 Excitation of Rare Gas-Halogen
Excimer Lasers

• There are two primary methods
• E-Beam (or nuclear) excitation
• Discharge pumping

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10.8.2.1 E-Beam (or nuclear) excitation

• Figure 1 Excitation of the
  rare gas-halide laser
• Energetic, High current electron beam is injected
  to the gas mixture.

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10.8.2.1 E-Beam (or nuclear) excitation

• Figure 1 Excitation of the
  rare gas-halide laser
• The electrons are rapidly attached to a halogen
  by a dissociative attachment process typified by

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10.8.2.1 E-Beam (or nuclear) excitation

• Figure 1 Excitation of the
  rare gas-halide laser
• Electrons-ion pairs are created by the electron
  beam in the gas mixture. i.e. is
  created

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10.8.2.1 E-Beam (or nuclear) excitation

• Figure 1 Excitation of the
  rare gas-halide laser
• The negative and positive ions get together in
  the presence of a third body, Usually another
  rare gas atom to form the excimer

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10.8.2.1 E-Beam (or nuclear) excitation

• Figure 1 Excitation of the
  rare gas-halide laser
• The third body (Ar) is necessary to share the
  excess energy of the reaction which is 6.54eV
  (The potential depression due to the coulomb
  attraction of and )

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10.8.2.2 Discharge pumping

• When the electron energy is low, it can only make
  elastic collisions with the majority rare gas.
• The small amount of energy lost in such a
  collision lead to merely warm the gas.
• The energy tail of the electron distribution can
  make inelastic collisions and create excited
  states. In this case ion channel is not
  significant.
• Formation of excimer states

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Problems of discharge-pumped lasers

• Halogen which is created from
  attaches the
  electrons
• Which leads to a negative dynamic resistance and
  a unstable discharge
• When too many electrons are present, then a
  super elastic process robs the energy from
  excimer state
• In this case, a low-current, high-energy
  electron beam is used to sustain the discharge
  process

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• Eg Most small commercial tabletop lasers.
• UV energy 50 to 100mJ/pulse
• width 10ns (power 10MW)
• repetition rate 500pps (average power
  50W)
• These are most efficient source of
  high-intensity UV radiation.

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