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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

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 Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Excimer e - + A → A* A* + B → AB* → AB + hν Immediately AB → A + B Two important facts: 1.The lower state does not exist! 2.No rotational/vibrational bands Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Excimer LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications Energy states of an excimer

Excimer Excited Dimers –F 2, Xe 2 ect. Excited Complexes (Exciplex) –Combination of rare gas atoms and halogen atoms –Ar, Kr, Xe –F, Cl, Br Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Excimer LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications ExcimerWavelength Ar nm Kr nm F2F2 157 nm Xe and 175 ArF193 nm CaF nm KrCl222 nm KrF248 nm Cl nm XeBr282 nm XeCl309 nm N2N2 337 nm XeF351 nm Many wavelength possibilities Depends upon the excited dimer Repetition rate from 0.05 Hz to 20 kHz High power: several 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 Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

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) Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Dye LASER Polyatomic organic molecules containing conjugated double bonds Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Dye LASER Polyatomic organic molecules containing conjugated double bonds Electrons move freely within the whole chain Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Dye LASER Polyatomic organic molecules containing conjugated double bonds Electrons move freely within the whole chain Can be described as a free electron in one dimensional potential well Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Dye LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications E n = h 2 N 2 /8mL 2

Dye LASER Selection rule: ∆S = 0 –S 0 → S 1 allowed Vibrational and rotational levels unresolved in liquid Fluorescence emission –S 1 → S 0 Losses: –Intersystem crossing S 1 → T 1 –Phosphoresence T 1 → S 0 –Absorption S 1 → S 2 T 1 → T 2 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

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) Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Dye LASER Academic –Tunable in a wide range of wavelengths Environmental –Pollution monitoring Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

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