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Waves, Light & Quanta. Tim Freegarde. Web Gallery of Art; National Gallery, London. Fra Angelico (c1387-1455) Museo del Prado (c1430). Carlo Crivelli (c1435-1495) St ä del, Frankfurt (c1482). Jan Van Eyck (c1395-1441) National Gallery of Art (c1434). Rays of light. ultramarine:. - PowerPoint PPT Presentation
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Rays of light
Jan Van Eyck (c1395-1441)National Gallery of Art (c1434)
Fra Angelico (c1387-1455)Museo del Prado (c1430)
Carlo Crivelli (c1435-1495)Städel, Frankfurt (c1482)
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Colour
Wilton Diptych (c1395-9)National Gallery
• ultramarine: lapis lazuli
sulphur (S3-)
Azzurro oltramarino si è un colore nobile, bello, perfettissimo oltre a tutti i colori; del quale non se ne potrebbe né dire né fare quello che non ne sia più. E per la sua eccellenza ne voglio parlare largo, e dimostrarti appieno come si fa. E attendici bene, però che ne porterai grande onore e utile.
Ultramarine blue is a colour that is noble, beautiful, the most utterly perfect of all colours; of which one can neither say nor do anything that it would not surpass. And because of its excellence, I wish to speak of it at length, and show you in detail how to make it. And pay attention, because it will bring you great honour and usefulness.
Il libro dell’arte (The Craftsman’s Handbook)
Cennino D' Andrea Cennini (~1400)
electronic absorption 600 nm
(red)
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Sinusoidal waves
kztrtxy sin,
• simple harmonic motion
• circular motion
,r kzt where
kztrkztr sin,cos
z
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Sinusoidal waves
0tt
0tt at ,
• wavenumber
2k
x
y
000 sin, tkxytxy
• spectroscopists’
1~ wavenumb
er
00~2sin txy
00
2sin txy
• wavelength
kxtytxy sin, 0
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Sinusoidal waves
0xx
0xx at ,
• angular frequency
2
t
y
000 sin, kxtytxy
• frequency
1 00 2sin kxty
00
2sin kxty
• period
kxtytxy sin, 0
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Birefringence
• asymmetry in crystal structure causes two different refractive indices
• opposite polarizations follow different paths through crystal
• birefringence, double refraction
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Optical polarization
• for any wavevector, there are two field components
• light is a transverse wave: perpendicular to E k
• any wave may be written as a superposition of the two polarizations
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Linear dichroism
• conductivity of wire grid depends upon field polarization
• electric fields perpendicular to the wires are transmitted
WIRE GRID POLARIZER
• fields parallel to the wires are absorbed
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Linear dichroism
• crystals may similarly show absorption which depends upon linear polarization• absorption also depends upon wavelength• polarization therefore determines crystal colour
TOURMALINE
• pleochroism, dichroism, trichroism
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Polarization in nature
• the European cuttlefish also has polarization-sensitive vision
• … and can change its colour and polarization!
MAN’S VIEW CUTTLEFISH VIEW (red = horizontal polarization)
CUTTLEFISH (sepia officinalis)
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Circular dichroism
• absorption may also depend upon circular polarization
• the scarab beetle has polarization-sensitive vision, which it uses for navigation
• the beetle’s own colour depends upon the circular polarization SCARAB BEETLE LEFT CIRCULAR
POLARIZED LIGHT
RIGHT CIRCULAR
POLARIZED LIGHT
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Optical activity (circular birefringence)
l-limonene(orange)
r-limonene(lemon)
CH2
CH3
HCH3 CH2
CH3
HCH3
CHIRAL MOLECULES
• optical activity is birefringence for circular polarizations
• an asymmetry between right and left allows opposing circular polarizations to have differing refractive indices• optical activity rotates the polarization plane of linearly polarized light• may be observed in vapours, liquids and solids
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Categories of optical polarization
• linear (plane) polarization• non-equal components in phase
• circular polarization• equal components 90° out of
phase• elliptical polarization
• all other cases
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Polarization notation
• circular polarization• right- or left-handed rotation
when looking towards source
• linear (plane) polarization• parallel or perpendicular to
plane of incidence
RCP plane of incidence
perpendicular
parallel
• traces out opposite (right- or left-) handed thread
• plane of incidence contains wavevector and normal to surface
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Brewster’s angle
ir
ri sincos
i
sin1
itan
• reflected light fully (s-) polarized
ir
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Brewster’s angle
www.paddling.net/sameboat/archives/sameboat496.html
ii
r
r
itan• reflected light fully (s-) polarized
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