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

2 2 Waves, Light & Quanta RAYS AND IMAGES mirrors, lenses and telescopes propagation matrices WAVELENGTH AND POLARIZATION prisms, rainbows and dispersion polarization, birefringence and polarizers Fermat’s principle and Snell’s lawpolarization propagation matrices WAVE PHENOMENA amplitudes and interference Huygens construction and diffraction SUPERPOSITIONS spectra and spectrometers beats and coherence QUANTA AND WAVE- PARTICLE DUALITY electrons: diffraction and tunnelling wavepackets and uncertainty photons: energy and momentum slits, gratings and interferometers

3 3 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 Maxwell’s electromagnetism, Einstein’s relativity

4 Radiation pressure © Malcolm Ellis Comet Hale-Bopp, 1997 intensity (energy per unit time per unit area) pressure (momentum per unit time per unit area) light carries both energy and momentum (Maxwell’s electromagnetism) sun sunshine torque (angular momentum per unit time per unit area)

5 Radiation pressure © Malcolm Ellis Comet Hale-Bopp, 1997 intensity (energy per unit time per unit area) pressure (momentum per unit time per unit area) light carries both energy and momentum (Maxwell’s electromagnetism) torque (angular momentum per unit time per unit area) R A Beth, Phys Rev (1936) Crookes radiometer sun sunshine

6 Pinhole camera foil screen pinholeobject image range of image points for each point on objectLARGE PINHOLE: reduce pinhole size for sharper image

7 7 Pinhole camera x range of image points for each point on objectLARGE PINHOLE: reduce pinhole size for sharper image diffraction causes blurring of imageSMALL PINHOLE: increase pinhole size for sharper image

8 8 Pinhole camera x amplitude intensity range of image points for each point on objectLARGE PINHOLE: reduce pinhole size for sharper image diffraction causes blurring of imageSMALL PINHOLE: increase pinhole size for sharper image optimum pinhole size when

9 9 Pinhole camera range of image points for each point on objectLARGE PINHOLE: reduce pinhole size for sharper image diffraction causes blurring of imageSMALL PINHOLE: increase pinhole size for sharper image Dimitrova & Weis, Am J Phys 76, 137 (2008) optimum pinhole size when x

10 Light and optics RAYS straight propagation paths least time (Fermat’s principle) reflection, refraction, lenses, telescopes, microscopes directrix focus PHOTONS Planck, Compton, Einstein WAVES Huygens’ description of propagation, reflection, refraction polarization, colour (wavelength, frequency) diffraction, interference, beats, interferometers Maxwell’s electromagnetism, Einstein’s relativity

11 Michelson interferometer interference by division of amplitude beamsplitterdetector source δxδx

12 Michelson interferometer interference by division of amplitude beamsplitterdetector source δxδxδxδx sodium doublet optique-ingenieur.org chemistry.oregonstate.edu FTIR: Fourier transform infrared

13 Diffraction grating x

14 Grating spectrometer scope.pari.edu

15 Blackbody radiation RAYLEIGH-JEANS DISTRIBUTION consider modes of given volume of space assume equipartition: average energy kT per mode mode density hence wavelength intensity Rayleigh- Jeans

16 Blackbody radiation intensity Rayleigh- Jeans observed spectrum BLACK BODY perfect absorber, hence ‘ideal’ emitter no spectral features beyond Planck curve wavelength ULTRAVIOLET CATASTROPHE classical thermodynamics predicts monotonic increase with frequency quantization of radiation field supplies required correction

17 Blackbody radiation intensity Rayleigh- Jeans observed spectrum BLACK BODY perfect absorber, hence ‘ideal’ emitter no spectral features beyond Planck curve wavelength ULTRAVIOLET CATASTROPHE classical thermodynamics predicts monotonic increase with frequency quantization of radiation field supplies required correction PLANCK’S DERIVATION hence modify equipartition: energy quantized in units of

18 Messenger Lecture Richard P. Feynman ( ) Nobel prize 1965 Probability and Uncertainty – the quantum mechanical view of nature Messenger series of lectures (lecture 6), Cornell University, 1964 published as The Character of Physical Law - Penguin