The Electromagnetic Spectrum 1
The term electromagnetic radiation includes the entire spectral range
from atmospheric radiation at 1023 Hz to radio waves at few Hz.
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The Electromagnetic Spectrum 2
Sizes of Physical Objects:
10+28 m
10+21 m
10+16 m
10+9 m
10+7 m
10+3 m
diameter of observable universe
diameter of Milky Way galaxy
distance to nearest star
diameter of sun
diameter of earth
diameter of city
10+0 m diameter of (overfed) human (1 m)
10-5 m diameter of a blood cell
10-8 m diameter of a large molecule
10-9 m diameter of a small molecule
10-10 m diameter of an atom
10-14 m diameter of atomic nucleus
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Nature of Light 1
Geometric optics:
Treating light as a bundle of rays enables to describe the distribution of
light as well as the creation of images. No information is provided about
the interaction of light with matter.
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Nature of Light 2
Wave optics:
Based on Maxwells's theory, light can be described as periodic oscillation of
electric and magnetic vectors in time and space. Resulting, optical phenomena
such as diffraction, interference and polarization can be explained.
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Nature of Light 3
Quantum optics:
Only light described as flux of discrete particles without mass, so called photons,
allows explaining the absorption and emission of light. The energy of photons is
proportional to the frequency of the radiation.
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Spectroscopic Methods
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When do we use which model?
Wave optics:
Ø Reflection
Ø Transmission
Ø Diffraction
Ø Refraction
Ø Scattering
Ø Polarization
Quantum optics:
Ø Photoelectric effect
Ø Emission of radiation (Line- and Bandspectra)
Ø Absorption of radiation
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Basic Parameters 1
Wave optics:
Ø Amplitude (A): represents the length of the electric field component
at the maximum of the wave.
Ø Wavelength (λ): the linear distance between two corresponding
points within successive sine-waves, e.g. the distance between two
maxima.
Ø Wavenumber (ν): defined as 1/λ in centimeters, allows to directly
correlate the wavelength to the frequency via ν = kν with k as
proportionality constant.
Ø Frequency (ν): number of oscillations of the electromagnetic field
per second (s-1 or Hz). ν is determined only by the light source and
thus remains constant!
Ø Period (p): time in s required for sucessive maxima and minima to
pass through a fixed point in space.
Ø Velocity of propagation (ν i): νi = ν λ i
in vacuum: velocity independent of wavelength, c = 2.998*108 ms-1
(νi depends on the composition of the medium!)
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Basic Parameters 2
Wave optics:
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Basic Parameters 3
Ø Power (P): energy of the beam that reaches a given area per s.
Hence, the power is defined as energy/time. The total emitted power of a
light source is called radiative flux Φ, e.g. In Watt.
Ø Intensity (I): power of the beam or radiative flux detected at a certain
area A or at a certain dihedral angle Ω [steradiant, sr].
I = Φ/A [W/m2]
⇒ The same radiative
flux or power leads to a
higher intensity if confined
to a smaller illuminated area.
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Basic Parameters 4
General:
Ø Polychromatic radiation: light is usually not homogeneous with
respect to the wavelength but consisting of light quanta with different
energy.
(broad-band (polychromatic) emitters, e.g. black bodies,
halogen lamps, gas discharge lamps, etc.)
Ø Monochromatic radiation: light with a narrow energy distribution
curve or, ideally, light quanta of a single frequency (energy).
(narrow-band (monochromatic) emitters, e.g. light emitting diode (LED)
laser, etc.)
Ø Coherence: the property that the multitude of individual wave trains
emitted from a light source have a fixed phase relation
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