Waves, Light & QuantaTim Freegarde

Web Gallery of Art; National Gallery, London

2

Young’s double slit diffraction

x

s

a

amplitude

intensity

d

d2

d

3

Single slit diffraction

x

y

s

a

amplitude

intensity

4

Diffraction grating

x

d

y

s

a

• place secondary sources along wavefront

• ...and trigger when wavefront arrives

• apply to sinusoidal waves by taking into account the phase with which components arrive• combine by adding the amplitudes

• contributions may therefore interfere constructively or destructively

INTERFERENCE

Grating spectrometer

scope.pari.edu

6

Michelson interferometer

• interference by division of amplitude

beamsplitter detector

source

δx

7

Michelson interferometer

• interference by division of amplitude

beamsplitter detector

source

δx δx

Michelson interferometer

• interference by division of amplitude

beamsplitter detector

source

δx δx

• sodium doublet

optique-ingenieur.org

chemistry.oregonstate.edu

• FTIR: Fourier transform infrared

9

Newton’s rings

diffuser

beam-splitter

lens

plate

s

r

• apply to sinusoidal waves by taking into account the phase with which components arrive• combine by adding the amplitudes

• contributions may therefore interfere constructively or destructively

www.sciencebuddies.org

10

Michelson stellar interferometer

x

2

2s

a

intensity

d

d2

d

1

1s

11

Michelson stellar interferometer

ad

12

Michelson stellar interferometer

Mount Wilson Observatory www.mwoa.org

13

Coherence

NON-POINT OBJECTS• many independent emitters, e.g. different atoms in

star• spatial extent (angular width) determines fringe visibility• partial visibility when phase difference partially defined• coherence is a measure of extent to which the phase difference is known

• degree of coherence 2

221

2112

EE

EE

• (approximate expression – requires complex numbers)

• complex degree of coherence

2211

2112

EEEE

EE

14

Light and optics

RAYS• straight propagation paths

• least time (Fermat’s principle)

• reflection, refraction, lenses, telescopes, microscopes

WAVES• Huygens’ description of propagation, reflection,

refraction• polarization, colour (wavelength, frequency)

• diffraction, interference, beats, interferometers

directrix

focus

PHOTONS• Planck, Compton, Einstein

• Maxwell’s electromagnetism, Einstein’s relativity