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Introduction to Lasers

Introduction to Lasers. 자연과학부 나종훈. LASER 의 시초 Atomic Structure Transitions between Laser states Population Inversion Pulsed Operation Power and Energy The elements for Lasers Transverse & Longitudinal Modes. 목 차.

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Introduction to Lasers

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  1. Introduction to Lasers 자연과학부 나종훈

  2. LASER의 시초 Atomic Structure Transitions between Laser states Population Inversion Pulsed Operation Power and Energy The elements for Lasers Transverse & Longitudinal Modes 목 차

  3. Microwave Amplification by the Stimulated Emission of Radiation -1954, 24-GHz ammonia device Light Amplification by Stimulated Emission of Radiation -1957, First idea of LASER(using Fabary Perot cavity as part of LASER) The Beginning of LASER

  4. ATOMIC STRUCTURE

  5. Spontaneous · Stimulated Emission E=hν=E2-E1 h: Planck’s constant ν: frequency of the laser light Ideal laser light are at exactly the same frequency (wavelength) & all the photons are in phase.

  6. N2/N1=Exp-(E2-E1)kBT Population Inversion Population ratio between two states N2: population in the upper state N1: population in the lower state kB: Boltzman’s constant T: temperature (K) Gain 달성 조건: Population in the upper laser state is greater than the population in the lower state. A pulse of light, an electrical spark or a chemical reaction can all be used to populate the upper laser state. → pumping

  7. Q-swicthing To concentrate the laser energy into the pulse Mode locking To shorten the width of the pulse in time Pulsed Operation Effective for reducing the laser’s heating (cf: semiconductor diode lasers)

  8. Average Power : The power of a continuous wave laser Pavg=Epulse*Rreprate Peak power : Epulse/tpulse Average energy density : The energy(J) per unit area Average power density : The energy power per unit area Peak power density : The peak power per unit area Power and Energy

  9. Monochromaticity & Coherency • Monochromaticity • A group of photons at exactly one frequency • Coherency - A group of photons with the same relative phase

  10. Gain Materialsolid(Nd:YAG,Ruby,GGG,GSGG,alexandrite,emerald,Cr:Sapphire,Ti:Sapphire,AlGaAs) Liquid(dye,chelate) Gas(Krypton,argon,nitrogen,helium-neon,CO2,KrF,XeCl) Plasma(X-ray,free-electron) Pumping source To provide the energy to set up the energy states so that stimulated emission can occur optically to be pumped using other lasers(most solid-state lasers) electrically to be pumped using a pn-junction(semiconductor diodes) Resonant cavity physically shorten the laser tailor the profile of the electromagnetic mode The elements for Lasers

  11. Transverse & Longitudinal Modes • TEM(transverse electromagnetic mode) • The frequencies of Longitudinal electromagnetic modes of the cavity(v=p*c0/2nL) • A laser can only lase at those wavelengths(longitudinal mode) for which an integral multiple of wavelengths fit into the cavity.

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