Presentation on theme: "Zero-Phonon Line: transition without creation or destruction of phonons Phonon Wing: at T = 0 K, creation of one or more phonons 7. Optical Spectroscopy."— Presentation transcript:
Zero-Phonon Line: transition without creation or destruction of phonons Phonon Wing: at T = 0 K, creation of one or more phonons 7. Optical Spectroscopy at Cryogenic Temperatures
Mirror Image Absorption and fluorescence spectra are related by a mirror symmetry around the 0-0 transition
Intensity and Width of ZPL Intensity decreases steeply with T Width limited by excited-state lifetime and dephasing (thermal fluctuations)
Inhomogeneous Broadening Disorder and defects cause a spread of electronic transition frequencies
Single-Molecule Spectroscopy Spectral selection of single molecules
The first optical detection of a single molecule, via absorption (W. E. Moerner and L. Kador, Phys. Rev. Lett. 62 (1989) 2535) Detection of single molecules by fluorescence excitation (M. Orrit and J. Bernard, Phys. Rev. Lett. 65 (1990) 2716)
8. Two-Level System in a Laser Field Detuning from resonance Rabi frequency
Optical Saturation Saturation of the fluorescence excitation line of a single dibenzoterrylene molecule in a naphthalene crystal Maximum intensity and width as functions of the laser power
Transients: Optical Nutation Nutation transients without (left) and with (right) coherence damping
Antibunching histograms Antibunching at low temperature (left, pentacene in p-terphenyl) and at room temperature (right, terrylene in p-terphenyl)
Quantum Optics Light Shift of the optical transition Correlation histograms of a single-photon source
9. Triplet State(s) Only one triplet level: correlation function Two sublevels:
On- and Off-time Statistics From: Th. Basché, S. Kummer, Ch. Bräuchle, Nature 373 (1995) 132
Optically Detected Magnetic Resonance Microwave transfers populations between triplet sublevels, modifying the average fluorescence intensity … here for a pentacene molecule in a p-terphenyl crystal,
… or changing the off-time statistics, here for terrylene in p-terphenyl, A. C. J. Brouwer et al., Phys. Rev. Lett. 80 (1998) 3944.
Single nuclear spins ODMR of fully deuterated single pentacene molecules containing only C12 atoms (left), or one C13 atom in two different positions (center, right). The splitting is due to the nuclear spin J. Köhler et al., Science 268, 1995,1457.
10. External Fields Stark effect quadratic …or linear.
Shift of single terrylene molecule lines under modification of the carrier gas in a semiconductor (ITO) by an applied sawtooth voltage
Low-frequency localized acoustic modes
11. Spectral Diffusion Jumps or drift of the ZPL in spectrum Two-level Systems in Glasses Evidence for a single TLS in the correlation of a terrylene molecule in polyethylene
Spectral jumps in p-terphenyl crystals a: p-terphenyl b: terrylene Crystal structure 4 spectroscopic sites of terrylene in p-terphenyl
Spectral diffusion close to domain walls W. P. Ambrose et al. J. Chem. Phys. 95 (1991) Wall = 2D lattice of 2-level systems Random jumps spectral diffusion
12. Interacting Single Molecules Contact interactions Electron exchange Dipole-dipole coupling leads to ¨FRET, excitonic coupling
Exciton coupling in a dimer Energies
Bacterial Light-Harvesting Complex B800 ring B850 ring
Excitation spectra of single LH2’s Ensemble Individual Complexes A. van Oijen et al., Science 285 (1999) 400.
Exciton coupling in the B850 ring k=0 exciton k= ± 1 excitons split by distortion
Two Quasi-Resonant Molecules A new two-photon resonance appears at high laser intensity between two single- molecule lines C. Hettich et al., Science 298 (2002) 386.
Two-photon resonance Excitation of Molecule 1 Excitation of Molecule 2 Molecules are coupled!
13. Other Single Molecule Experiments Studies of soft matter and materials Other emitters, SC nanocrystals, color centers Blinking statistics Non-fluo. optical detection methods Photothermal detection Pump-probe and other nonlinear spectroscopies
Conclusion SM Microscopy at room T: –biophysics –material science SM Spectroscopy at room and low T: –molecular physics –quantum optics –solid state physics