1. Photon Physics Lourens van Dijk, April 7, 2009
The Excimer Laser
Photon Physics
Lourens van Dijk, April 7, 2009  
Maybe you know somebody who has had a laser treatment for his eyes. The laser used for that is an excimer laser.
Outline:
Principle
-reactions
Advantages
applications

2. The Principle Excimer: Excited Dimer
Noble gas and Halogen: Ar & F form complex  Exciplex
Stable in excited state; indirect pumping
Dimer: intermolecular forces

3. Reactions Gas: Ar and F Electrical discharge results:
F2  2 F
Ar  Ionize Ar+ + e-
F + e- (from Ar)  F-
Result: two ions, combining:
Ar+ + F-  ArF*
ArF*  ArF +‘hν’ (UV photon!)
ArF  not stable (repulsive)  Ar + F
Nl = 0 ☺
Corrosive F
UV photon

4. Applications Photolithography: production of IC’s
Ablation: material processing (1013 W/m2)
Pumping of dye lasers: extended absorption for UV
Medical applications
The invention, wikipedia: Samuel E. Blum
1981, Thanksgiving, turkey, beam cut cartilage with great precision
method for creating clean precise cuts in tissue (patent)
Photolithography: selectively remove some part of Thin Film
experimenting with short-pulse, ultraviolet lasers
Maybe you think that’s trivial, but you should hit upon the idea of placing a turkey in you laser beam.

5. Medical Applications:
Advantages
UV light, nm: Absorption over very short region, very precise  photolithography
high pulse intensity
Photo-etching: breaking chemical bonds  Separate cells (ablation), less heating
‘no’ damage to tissues around them
Medical Applications:
LASIK: Reshaping of the cornea
Treatment of Atherosclerosis: removing plaque  prevent cardiac death.
Kransslagader: coronary artery
Improvement optical properties
Next slides: appl

6. LASIK Incision into cornea
A flap of the outer corneal tissue is folded back.
Ablation by laser.
Advanced techniques: following eye
20/400  20/20
Deal with the problem itselfs.
Verdoven: apply/do a local anaesthetic
anaesthesia
Bulky device
Eyes our most important sense; no glasses/lenses
20/10 vision

7. Treatment of Atherosclerosis
Doctoral thesis, study of removing plaque and blood clot by using an excimer laser.
Cardiac death
Thin metal (guiding) wire in aorta
Catheter with laser is pushed over the wire
Alternatives
Blockage
Already:
-bypass and
-chemically reducing activity of the heart.

8. Pig aorta CW argon laser (400-500 nm)
10 atm
and subsurface temperature exceeds the surface temperature at the onset of ablation.
Distinct sound
With UV no popcorn effect
Ideal: absorbtion over a few micrometers (EOH)
Popcorn effect

9. Enormous expansion of water:
ρwater vapor = 0.81 kg/m3  1235 L per l water
Volume increase of factor 864
Insoluble  bubbles
Too large  damage of aorta (overstretch); keep fluence low
Kransslagader: coronary artery
70% water