Excimer and Dye lasers Helga Dgg Flosadttir Ntma

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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications – 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 LASER • Excited dimer Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications – 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 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 LASER Energy states of an excimer Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications

Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • 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 LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications Excimer Wavelength Ar 2 126 nm Kr 2 146 nm F 2 157 nm Xe 2 172 and 175 Ar. F 193 nm Ca. F 2 193 nm Kr. Cl 222 nm Kr. F 248 nm Cl 2 259 nm Xe. Br 282 nm Xe. Cl 309 nm N 2 337 nm Xe. F 351 nm • Many wavelength possibilities • Depends upon the excited dimer • Repetition rate from 0. 05 Hz to 20 k. Hz • High power: • several 10 -200 W

Excimer LASER • Micromaching Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications – 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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • Eye surgery for vision correction with Ar. F lasers at 193 nm • psoriasis treatment with Xe. Cl lasers at 308 nm • Pumping dye lasers (Xe. Cl)

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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • Liquid LASERs • Organic dyes solved in organic solvents • Pumped with a LASER and emit light via fluoresence

Dye LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • Organic polyatomic molecules with conjugated π-chains – Rhodamine, tetracene, coumarine, stilbene and more. • Solvent – Methanol, water or ethylene glycol • Additional chemicals added to prevent intersystem crossing and prohibit degration of the dye

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

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

Dye LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • 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

Dye LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications En = h 2 N 2/8 m. L 2

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

Dye LASER Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • Problems – Short lifetime of the S 1 state – Intersystem crossing and long lifetime of T 1 – 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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • 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 Excimer Function Chemicals Characteristic applications Organic Dye Chemicals Function Characteristic applications • Academic – Tunable in a wide range of wavelengths • Environmental – Pollution monitoring

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