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Waves, Light & Quanta

Waves, Light & Quanta. Tim Freegarde. Web Gallery of Art; National Gallery, London. electron wavelength. Davisson-Germer experiment. NICKEL TARGET. C Davisson & L H Germer, Phys Rev 30 705 (1927). ELECTRON DIFFRACTION. electrons behave like waves. Diffracting atoms.

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Waves, Light & Quanta

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

  2. electron wavelength Davisson-Germer experiment NICKEL TARGET C Davisson & L H Germer, Phys Rev 30 705 (1927) ELECTRON DIFFRACTION • electrons behave like waves

  3. Diffracting atoms E M Rasel et al, Phys Rev Lett 75 2633 (1995)

  4. molecule wavelength Diffracting molecules S Gerlich et al, Nature Physics 3 711 (2007) MOLECULE DIFFRACTION • molecules behave like waves

  5. + • circular orbits Bohr model of the hydrogen atom BOHR MODEL • quantized angular momentum • de Broglie wavelength • quantized energy levels • Hydrogen energy level measurements and calculations agree to 15 figures

  6. energy quantized in units of (h = Planck’s constant) • momentum quantized in units of • frequency determined by energy • de Broglie wavelength determined by momentum • angular momentum quantized in units of • angular momentum quantized in units of PHOTONS Quantum theory • blackbody radiation • photoelectric effect • Compton scattering PARTICLES • electron diffraction • atomic theory

  7. + • circular orbits Bohr model of the hydrogen atom BOHR MODEL • quantized angular momentum • de Broglie wavelength • quantized energy levels • Hydrogen energy level measurements and calculations agree to 15 figures

  8. energy • allowed energies 0 n = 3 n = 2 n = 1 Bohr model of the hydrogen atom n =  Rydberg constant • emission wavelengths

  9. energy • allowed energies n =  0 n = 3 n = 2 n = 1 Atomic line spectra Rydberg constant • emission wavelengths

  10. n =  energy n = 3 0 n = 2 universe-review.ca scope.pari.edu n = 1 Atomic line spectra Paschen Balmer Lyman

  11. energy • allowed energies 0 n = 3 n = 2 n = 1 Hydrogenic atoms n =  Rydberg constant • emission wavelengths

  12. singlet triplet Hg J Franck & G Hertz, Verh. Dtsch. Phys. Ges. 16 457 (1914) Franck-Hertz experiment • accelerate electrons through atomic vapour • periodic modulation of measured current • inelastic collisions when electron energy equals atomic transition energy G Rapior et al., Am J Phys 74 423 (2006)

  13. energy quantized in units of (h = Planck’s constant) • momentum quantized in units of • frequency determined by energy • de Broglie wavelength determined by momentum • angular momentum quantized in units of • angular momentum quantized in units of PHOTONS Quantum theory • blackbody radiation • photoelectric effect • Compton scattering PARTICLES • electron diffraction • atomic theory • Stern-Gerlach • discrete energy levels for bound particles • atomic theory

  14. SPONTANEOUS EMISSION energy 0 n = 3 n = 2 STIMULATED EMISSION n = 1 Quanta: absorption and emission of photons ABSORPTION n =  ABSORPTION absorption emission

  15. SPONTANEOUS EMISSION • thermal equilibrium STIMULATED  blackbody spectrum EMISSION • amplification of light if atomic population is inverted i.e. Quanta: absorption and emission of photons ABSORPTION EINSTEIN EQUATIONS • Einstein A and B coefficients ABSORPTION • spontaneous emission stimulated by vacuum field

  16. Waves, Light & Quanta: the LASER LIGHT AMPLIFICATION by Stimulated Emission of Radiation • Theodore Maiman, 16 May 1960 mirror beam splitter 693.4 nm ruby flash tube light amplifier optical resonator

  17. energy Waves, Light & Quanta: the ruby LASER mirror beam splitter 693.4 nm ruby flash tube metastable light amplifier optical resonator • Cr3+ ions in sapphire (Al2O3) absorb blue and green from flash light absorption emission • internal transitions to metastable state Cr3+ • spontaneous emission is amplified by passage through ruby • repeatedly reflected/amplified near-axial light builds up to form coherent laser beam

  18. mirror beam splitter ruby flash tube • narrow linewidth for long pulses ( ) Waves, Light & Quanta: beam characteristics 693.4 nm • as initial source recedes down unfolded cavity, emission approaches that from distant point source • divergence determined by diffraction by limiting aperture • focusable • constructive interference between reflections for certain wavelengths • long pulse  continuous wave (c.w.) • monochromatic • noise from spontaneous emission gives lower limit to linewidth • nonlinear processes have various effects in detail • Hecht section 13.1

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