excimer and dye lasers helga dögg flosadóttir nútíma ljósfræði vor 2008

Excimer and Dye lasers

Helga Dögg Flosadóttir

Nútíma Ljósfræði

Vor 2008

Outline

• Excimer LASER– Function– Chemicals– Characteristics– Applications in industry and research

• Organic Dye LASER– Chemicals– Function – Characteristics– Applications in industry and research

Excimer LASER

• N.G. Basov et al 1970– First excimer laser

– Xe(g)

– 172 nm

• Uversity of Cambridge, Kansas State University, Avco Everett Research laboratory, 1974– First exciplex excimer lasers– Simulataneously

• Lambda Physik 1977– First commercial excimer/exciplex laser– 10 MW

ExcimerFunctionChemicalsCharacteristicapplications

Organic DyeChemicalsFunction Characteristicapplications

Excimer LASER

• Excited dimer– Short lived molecule formed from one or two

species, at least one of which is in an electronically excited state

– May not be stable in ground state

• Excimer LASER: – Electron pumped LASER– Dimer (excimer)/complex (exciplex) formation– LASER radiation: relaxation from excited

state dimer to ground state



Excimer

e- + A → A*A* + B → AB* → AB + hν

ImmediatelyAB → A + B

Two important facts:1. The lower state does not exist!2. No rotational/vibrational bands



Excimer LASER



Energy states of an excimer

Excimer

• Excited Dimers– F2, Xe2 ect.

• Excited Complexes (Exciplex)– Combination of rare gas atoms and halogen

atoms– Ar, Kr, Xe– F, Cl, Br



Excimer LASER



Excimer Wavelength

Ar2 126 nm

Kr2 146 nm

F2 157 nm

Xe2 172 and 175

ArF 193 nm

CaF2 193 nm

KrCl 222 nm

KrF 248 nm

Cl2 259 nm

XeBr 282 nm

XeCl 309 nm

N2 337 nm

XeF 351 nm

•Many wavelength possibilities

•Depends upon the excited dimer

•Repetition rate from 0.05 Hz to 20 kHz

•High power:

•several 10-200 W

Excimer LASER

• Micromaching– Ink jet cartidges (drilling the nozzles)

• Radiation for changing the structure and properties of materials– Active matrix LCD monitors– Fiber bragg gratings– High temperature superconducting films

• “Short wavelength light bulb” in optical litography– Computer chips



Excimer LASER

• Eye surgery for vision correction with ArF lasers at 193 nm

• psoriasis treatment with XeCl lasers at 308 nm

• Pumping dye lasers (XeCl)



Outline

• Excimer LASER– Function– Chemicals used– Characteristics– Applications in industry and research

• Organic Dye LASER– Chemicals– Function – Characteristics– Applications in industry and research

Dye LASER

• Liquid LASERs• Organic dyes solved in organic solvents• Pumped with a LASER and emit light via

fluoresence



Dye LASER

• Organic polyatomic molecules with conjugated π-chains– Rhodamine, tetracene, coumarine, stilbene and more.

• Solvent– Methanol, ethanol, water or ethylene glycol

• Additional chemicals added to prevent intersystem crossing and prohibit degration of the dye

ONH+ HN

O

O

Cl-

Rhodamine 6G, 570-610

NH

O+NH

Acridine red, 600-630 nm

O

O

H

OH

H

OH

OH

H

HH

O

HO

HO O

Esculin, 450-470



Dye LASER

• Polyatomic organic molecules containing conjugated double bonds



Dye LASER


• Electrons move freely within the whole chain



Dye LASER


• Electrons move freely within the whole chain

• Can be described as a free electron in one dimensional potential well



Dye LASER



En = h2N2/8mL2

Dye LASER

• Selection rule: ∆S = 0– S0 → S1 allowed

• Vibrational and rotational levels unresolved in liquid

• Fluorescence emission– S1 → S0

• Losses:– Intersystem crossing

• S1 → T1

– Phosphoresence• T1 → S0

– Absorption• S1 → S2

• T1 → T2



Dye LASER

• Problems– Short lifetime of the S1 state– Intersystem crossing and long lifetime of T1– Thermal gradients produce refractive gradient

• Operation– Pulsed laser action– Circulation of dye solution– Pumping – another laser such as

• Nitrogen laser (UV-visible)• Excimer laser (UV-visible)• Nd:YAG laser (visible)



Dye LASER

• Vibration and rotational energy levels not resolved– Broad emission spectrum– tunable

• Wide selection of dyes for different emission wavelength ranges and absorbance

• Very short pulses achievable



Dye LASER

• Academic– Tunable in a wide range of wavelengths

• Environmental– Pollution monitoring



Thank you!

excimer and dye lasers helga dögg flosadóttir nútíma ljósfræði vor 2008

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