Transcript Lasers.ppt
Spectrophotometer
Light Sources:
Lasers
L.A.S.E.R.
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
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
Higher energy levels must be more
“populated” than lower levels in order for
lasing to occur.
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
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
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)*
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.)
solid-state: lasing material distributed in a
solid matrix (λ=1064nm; IR)
dye: use complex organic dyes (e.g.:
rhodamine 6G) in liquid solution or suspension
as lasing media (broad wavelength range).
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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