Transcript Lasers.ppt

Spectrophotometer
Light Sources:
Lasers
L.A.S.E.R.
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Acronym for: light amplification by
stimulated emission of radiation
Basic principle of lasing: population
inversion
Laser light is typically monochromatic –
emitting only one wavelength
Cost as varied as possible wavelength
range: from two-dollar pointers to milliondollar devices
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Laser Wavelengths
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Energy Absorption
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Energy absorption propels molecules to a
higher energy level.
In order for the molecules to move to the
excited state, they must absorb energy
from heat, light or electricity.
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Population Inversion
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Higher energy levels must be more
“populated” than lower levels in order for
lasing to occur.
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Once in the excited state, the molecule
will begin returning to the ground state,
resulting in the release of energy in the
form of a photon.
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- Harris, Daniel C. Quantitative Chemical Analysis. 6th ed.
New York: W.H. Freeman and Company, 2003.
Energy Emission
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From the excited state, molecules begin
to relax, releasing energy in the form of
photons of specific wavelengths
(colors), determined by the state of the
electron’s energy at release.
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Properties of Laser Light
Consists of only one wavelength
(monochromatic).
 Wave fronts of all the photons are
“launched in unison,” all moving in
step with the others (coherent).
 Strong, concentrated, tight beam
(directional).
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Types of Lasers
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excimer: reactive gases (e.g.: chlorine and
fluorine), mixed with inert gases (e.g.: argon,
krypton or xenon). When electrically stimulated,
a pseudo molecule (dimer) is produced. (λ = UV
range when lased)*
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gas: primary output of visible red light. CO2
lasers emit energy in the far-infrared; used for
cutting hard materials.
* UV light is most difficult to obtain due to it high
energy wavelength.
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Types (cont.)
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solid-state: lasing material distributed in a
solid matrix (λ=1064nm; IR)
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dye: use complex organic dyes (e.g.:
rhodamine 6G) in liquid solution or suspension
as lasing media (broad wavelength range).
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semiconductor: (aka: diode lasers); are
not solid-state lasers, but electronic devices.
Generally very small and use low power, found
in laser printers and cd-players.
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