An Introduction to AMO Physics - Department of Physics PDF
Preview An Introduction to AMO Physics - Department of Physics
An Introduction to AMO Physics Cass Sackett UVA What is AMO? = Atomic, molecular, and optical physics Linked because share basic approach: - Study “simple” quantum systems with high precision - Learn to control systems for applications - Central tool: laser Purpose of Talk Introduce key background ideas of AMO Helpful for subsequent talks Aimed at new students Outline I. Atoms and molecules Hierarchy of structures, notation II. Driving transitions Transition rate, saturation, coherent evolution III. Lasers Basic theory, types of laser IV. Frequency conversion Nonlinear response, phase matching V. AMO at UVA Groups, courses Atoms Simplest atom: hydrogen Energy levels have hierarchy mc2 Highest level: Coulombic E = - a 2 n 2n2 e2 1 a = = fine structure constant ep h 4 c 137 0 1 = - Often write E using atomic units n 2n2 a unit of energy = mc2 2 = Hartree = 27.2 eV Label states with n, l: 3d state has n = 3, l = 2 Fine structure Spin orbit coupling correlates L and S Use J = L +S Relativistic effects shift energy levels a Fractional shift ~(Z )2 for atomic number Z More important for heavier atoms Energy levels split by J J = 5/2 (6 states) ⇒ 3d J = 3/2 (4 states) (10 states) Notation: n 2S+1L J So “3 2D ” means n = 3, S = ½, L = 2, J = 3/2 3/2 Hyperfine structure Electronic angular momentum J coupled to nuclear angular momentum I via magnetic moments ⇒ Total momentum F = I+J Hydrogen has I = ½: F = 2 ⇒ 3 2D 3/2 F = 1 nuclear moment » · Energy scale FS scale electron moment Typically about 10-3 Other atoms Alkali atoms (Li, Na, K, Rb, Cs) have one valence electron + core electrons Act like H, but levels shifted due to core Rb: 6 S -13500 cm-1 1/2 units cm-1 = wave numbers 4 D 3/2 -14300 cm-1 1 eV = 8050 cm-1 4 D 5/2 = inverse of corresponding 517 nm wavelength 5 P -20800 cm-1 3/2 5 P -21000 cm-1 1/2 497 nm 780 nm 5 S -33600 cm-1 1/2 Multielectron Atoms More than one valence electron = more complex l Multiple s ’s and ’s, couple in different ways i i = ∑l = ∑ = + Typically L S s J L S i i Label state with L, S and J: Calcium: 1S (4s5s) 33300 cm-1 0 31500 3S (4s5s) 0 300 nm 1P (4s4p) 23700 1 1D (4s3d) 21900 2 3D (4s3d) 20300 1,2,3 3P (4s4p) 15300 0,1,2 422 nm 653 nm 1S (4s2) 0 cm-1 0 Molecules Put two atoms together, even more fun! Interact via molecular potential V(R) = energy as function of nuclear separation R Born-Oppenheimer approximation: - Fix nuclei at spacing R - Find electronic energies E (R) n - Use E (R) as potential for nuclear motion n Usually valid (m << m ) e N → At large R, E (R) E + E atomic energies n n1 n2 lots of quantum numbers! Alkali diatom ground state potential: E Pauli exclusion Spin triplet R Attractive van der Waals bound states Spin singlet Nuclei move in V(r): have own eigenstates and energies vibrational and rotational quantum numbers
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