Lec-4 Laser Fundamentals & its Applications 17 Feb 2011 P-2

Lec-4 Laser Fundamentals & its Applications 17 Feb 2011 P-2

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1 Photonic Network By Dr. M H Zaidi Population Inversion Hence, population inversion is a pre-requisite for amplification. Two most common excitation techniques are light and electricity. Practical Lasers involve 3 or 4 energy levels Three level Lasers are not ideal since ground state is Lower energy level Resonant cavity extracts energy from medium with population inversion. Photonic Network By Dr. M H Zaidi Population Inversion Highly exited level Excitation Laser Transition Population Inversion Between these 2 states Meta Stable State Three level system Ground State
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2 Photonic Network By Dr. M H Zaidi Population Inversion Highly exited level Excitation Laser Emission Upper Layer (Meta Stable) Matural Depopulation Population Inversion Between these states Ground State Four level system Photonic Network By Dr. M H Zaidi Laser Exposition Four General Categories of Lasers. • Gas Lasers • Solid State Lasers (Doped Insulators) • Semiconductor Lasers • Dye Lasers
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3 Photonic Network By Dr. M H Zaidi Laser exposition Gas Lasers Most Gas Lasers are pumped by electric discharge. He-Ne, Argon and CO 2 Lasers are quite popular. Salient features Visible region operation. Spectral purity Coherence Super beam quality. Uses Alignment, Signal and image processing applications Photonic Network By Dr. M H Zaidi Laser exposition Electric Power Supply Electrode Electric Discharge Laser Gas Rear Mirror Outer Mirror Laser Beam Generic Gas Laser
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Photonic Network By Dr. M H Zaidi He-Ne-laser •pump He to metastable state (20.61 eV) •transfer excitation to Ne metastable state (20.66 eV) •laser transition •spontaneous emission (2 times) to deplete lower level (-> low pumping) •not very efficient! (20.6 eV vs 2 eV) Photonic Network By Dr. M H Zaidi Laser exposition Solid state Lasers Most common light emitters are Cr +3 , Na +3 , Er +3 and HO +3 ions. Na-YAG Lasers are most popular. Salient features High power output. Spectral purity.
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This note was uploaded on 06/03/2011 for the course IT ISE808 taught by Professor Mr.tayyab during the Spring '11 term at College of E&ME, NUST.

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Lec-4 Laser Fundamentals & its Applications 17 Feb 2011 P-2

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