Scientists
Electromagnetic waves
University of Pécs, Faculty of
Medicines, Dept. Biophysics
physicists, chemists, astronomers
• Sir Isaac Newton
• Sir William Herschel
• Johann Wilhelm Ritter
• Joseph von Fraunhofer
• Robert Wilhelm Bunsen
• Gustav Robert Kirchhoff
• Albert Einstein
• Louis-Victor de Broglie
• James Clerk Maxwell
• Heinrich Rudolf
- Dispersion (1664)
- IR (1800)
- UV (1801)
- lines in the solar spectra (1814)
- interpretation of lines (1861)
- interpretation of lines (1861)
- light quantum (photon) (1904)
- matter-waves (1924)
- EM radiation theoretically (1864)
- EM radiation pragmatically (1888)
October 2013
The light
Electromagnetic
spectrum
Electromagnetic wave
Transversal
wave
electric field strength vector
wavelength
E
x
B
x
magnetic field
strength- vector
The vectors of the electric and the magnetic gradients
are perpendicular to each other and to the direction of
the propagation of the wave.
• James Clerk Maxwell (1864)
• Heinrich Rudolf (1888) confirmed
verified their existence theoretically. their existence experimentally.
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The spectrum
Kirchhoff’s Laws
• Spallation of one wave e.g. electromagnetic wave to its
component frequencies.
• One intensity-like quantity represented as the function of
an energy-like quantity.
First law: a hot dense gas
at high pressure produces
a continuous emission
spectrum of all colours.
(Thermal radiation.)
energy and energy-proportional
quantities (e.g. frequency,
wavelength, wavenumber)
absorption
intensity, count rate (e.g. measurement
of radioactivity), number of photons,
transmittancy, absorbancy (extinction,
OD)
Second law: hot rarefied gas at low pressure
produces an emission line spectrum (bright
spectral lines in front of a dark background).
Third law: when light from a hot dense gas
passes through a cooler gas, it produces an
absorption line spectrum (bright spectrum with
a number of dark, fine lines).
 (nm)
Line spectra (emission) of some
elements
The appearance of the spectra
• line-type (atoms)
• band (molecules)
• continuous (heated materials)
He
I
Hg
n
Na
Continuous emission
Ne
Line-type emission
Ar
Line-type absorption
Joseph von Fraunhofer
Interaction of the light with matter
(1787–1826)
• Quanted energy uptaking (photon)
• Interaction of electromagnetic wave
with atomic system (matter):
• reflection
• absorption
• transmission
• (scattering)
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Electric energy levels of the atoms
Energy level system of molecules
Bohr- and the quantummechanical atom model
Postulates:
• 1. Electrons can only circle
around the nucleus at definite
levels (does not emit or
absorb energy) – stationary
levels (unchanging).
• 2. Atoms absorb or emit
radiation only when the
electrons
abruptly jump
between
the
different
stationary levels, states.
Important physical quantities and
relations
Frequency:
n or f
(1/s)
v=λ·f
Wavelength:
 (m)
-1
Wavenumber: n (cm )
Energy:
Extinct. coeff.:
E (J)
c
v
n=c/v
1

h.f
Einstein: energy of a photon (light-quantum)
 (M-1cm-1 or (mg/ml)-1cm-1)
The dual nature of the light
Region
Wavelength range (mm)
Wavenumber range (cm-1)
Near
0.78 - 2.5
12800 - 4000
Middle
2.5 - 50
4000 - 200
Far
50 -1000
200 - 10
The most useful I.R. region lies between 4000 - 670cm-1.
Wave
(propagation)
Particle
(interaction)
• Diffraction
• Interference
• Polarization
• photoeffect
• Compton-effect
Albert Einstein (1905) : photoelectric effect
photon (light quantum), its energy: E = h·n (or E = h·f)
Louis-Victor de Broglie (1924) : Matter-waves theory
(All materials have wave nature as well.)
λ = h/p, where p is the impulse => λ = h/m·v
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Interference
Huygens-Fresnel principle
1. All points on a wave front can be considered as
point sources for the production of spherical
secondary wavelets.
2. The interference of the secondary wavelets
determines the further behaviour of the wave.
a
x  s1  s2  a  sin 
To achieve max. gain:
To achieve max. weakening:
a  sin   n  
a  sin   (n  12 )  
Linearly polarized light
Linearly polarized light
Polarization
The dual nature of the light
Wave
(propagation)
Particle
(interaction)
• Diffraction
• Interference
• Polarization
• photoeffect
• Compton-effect
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Spectroscopy
Photo- and Compton-effect, pair production
absorption
Spectra: The distribution of the intensity of the electromagnetic wave
in terms of wavelength. (Greek: picture, colour)
-scopo-, scop-, scept-, skept-, -scope-, -scopy, scopia, -scopic, -scopist
Greek: see, view, sight, look at, examine
 (nm)
•
Studies with EM radiations (e.g. light)
http://nagysandor.eu/harrisonia/XRayInteract_HU.html
Types and methods of spectroscopy
1. Spectroscopy of electric (atomic) energy levels
Intensity - wavelength (frequency):
• VIS, IR, UV, Röntgen, Raman, Mössbauer,
• ESR, NMR, CT, MRI ...
Lifetimes of energy states:
• fluorescence/phosphorescence lifetime
The purposes of the spectroscopy
Qualitative and/or quantitative cognition of matter:
 Analysing the quality („finger-print”)
 Analysing the quantity (intensity)
 Structural information (conformation)
To follow the time scaled change of matter:
(time-resolved spectroscopy)
Polarisation (anisotropy):
• anisotropy decay, CD-spectroscopy
 Changes of chemical constitution (e.g. under chemical reaction).
 Structural changes (acceptable for fast kinetic
measurements)
2. Spectroscopy of radioactivity
We can not see the molecule, but on the basis of the (change of
the) spectrum and with the help of our physical knowledge we
can implicate its structure.
(α-, β-, γ-particles, neutron, neutrino)
...
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