Waves, Light & Quanta Tim Freegarde Web Gallery of Art; National Gallery, London

2 Rays of light Jan Van Eyck (c ) National Gallery of Art (c1434) Fra Angelico (c ) Museo del Prado (c1430) Carlo Crivelli (c ) Städel, Frankfurt (c1482)

3 Colour Wilton Diptych (c1395-9) National Gallery ultramarine:lapis lazuli sulphur (S 3 - ) 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 dellarte (The Craftsmans Handbook) Cennino D' Andrea Cennini (~1400) electronic absorption 600 nm (red)

4 Colour Methuselah (C12) Canterbury Cathedral Magi and Herod (C12-13) Canterbury Cathedral

5 The prism

6 Colour

7 Rainbows

8 i i i r r r r x r r

9 Rainbows i i i r r r r x r r

10 Rainbows i i i r r r r x r r

11 Rainbows

12 Rainbows

13 Rainbows

14 Sinusoidal waves simple harmonic motion circular motion where z

15 Sinusoidal waves at, wavenumberspectroscopists wavenumber wavelength

16 Sinusoidal waves at, angular frequency frequency period

17 Birefringence asymmetry in crystal structure causes two different refractive indices opposite polarizations follow different paths through crystal birefringence, double refraction

18 Optical polarization for any wavevector, there are two field components light is a transverse wave: perpendicular to any wave may be written as a superposition of the two polarizations

19 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

20 Malus law WIRE GRID POLARIZER amplitude transmission intensity transmission

21 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

22 Polarization in nature the European cuttlefish also has polarization-sensitive vision … and can change its colour and polarization! MANS VIEWCUTTLEFISH VIEW (red = horizontal polarization) CUTTLEFISH (sepia officinalis)

23 Circular dichroism absorption may also depend upon circular polarization the scarab beetle has polarization- sensitive vision, which it uses for navigation the beetles own colour depends upon the circular polarization SCARAB BEETLELEFT CIRCULAR POLARIZED LIGHT RIGHT CIRCULAR POLARIZED LIGHT

24 Optical activity (circular birefringence) l-limonene (orange) r-limonene (lemon) CH 2 CH 3 H CH 2 CH 3 H 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

25 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

26 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

27 Polarization by scattering cdoswell.com/tips3.htm

28 Brewsters angle reflected light fully (s-) polarized

29 Brewsters angle reflected light fully (s-) polarized

30 Characterizing the optical polarization wavevector insufficient to define electromagnetic wave we must additionally define the polarization vector e.g. linear polarization at angle