Ultrafast Laser Spectroscopy - Laser Pulse Generation and...

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Unformatted text preview: Laser Pulse Generation and Ultrafast Pump-Probe Experiments By Brian Alberding Goals Basic Laser Principles Techniques for generating pulses Pulse Lengthening Pulse Shortening Ultrafast Experiments Transient Absorption Spectroscopy L.A.S.E.R L ight A mplification by S timulated E mission of R adiation Basic Laser Light Sources Gain medium Mirrors R = 100% R < 100% I I 1 I 2 I 3 Laser medium I R. Trebino Laser Cavity Gain Medium E 1 E 2 BN 1 I = rate of Stimulated absorption Einstein Coefficients E 2 E 1 E 2 E 1 BN 2 I = rate of Stimulated emission AN 2 = rate of Spontaneous emission E = h To achieve lasing: Stimulated emission must occur at a maximum (Gain > Loss) Loss: Stimulated Absorption Scattering, Reflections Energy level structure must allow for Population Inversion E 2 E 1 Obtaining Population Inversion sat I = h d N BIN BI N AN A N dt = -- +- 2 d N BI N AN A N dt = - +- Laser Transition Pump Transition Fast decay Fast decay 1 2 3 2 1 N 2 N 1 Laser Fast decay Laser Transition Pump Transition 1 2 3 2-level system 3-level system 4-level system 1 / sat N N I I = + 1 / 1 / sat sat I I N N I I- = + d N BIN BI N A N dt - = + + / 1 / sat sat I I N N I I = - + Population Inversion is obtained for N < 0 (N = N 1 N 2 ) Summary Basic Laser Source light Reflective Mirrors (cavity) Gain Media Energy Level Structure Population Inversion Pumping Rate Upper laser State Lifetime Upper laser State Lifetime > Cavity Buildup time Laser Transition Pump Transition Fast decay Fast decay 1 2 3 Types of Lasers Solid-state lasers have lasing material distributed in a solid matrix (such as ruby or neodymium:yttrium-aluminum garnet "YAG"). Flash lamps are the most common power source. The Nd:YAG laser emits infrared light at 1.064 nm. Semiconductor lasers , sometimes called diode lasers, are pn junctions....
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This note was uploaded on 02/14/2012 for the course CHEMISTRY 101 taught by Professor Louie during the Spring '11 term at Chemnitz University of Technology.

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Ultrafast Laser Spectroscopy - Laser Pulse Generation and...

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