Spontaneous emission

About: Spontaneous emission is a research topic. Over the lifetime, 12855 publications have been published within this topic receiving 323684 citations.

Continuum generation from single gold nanostructures through near-field mediated intraband transitions

Abstract: A broad visible and infrared photoluminescence continuum is detected from surface-plasmon-enhanced transitions in gold nanostructures. We find that the ratio of generated infrared to visible emission is much stronger for gold nanostructures than for smooth gold films. While visible emission is well explained by interband transitions of d-band electrons into the conduction band and subsequent radiative recombination, the strong infrared emission cannot be accounted for by the same mechanism. We propose that the infrared emission is generated by intraband transitions mediated by the strongly confined fields near metal nanostructures (localized surface plasmons). These fields possess wave numbers that are comparable to the wave numbers of electrons in the metal, and the associated field gradients give rise to higher-order multipolar transitions. We compare photoluminescence spectra for single gold spheres, smooth and rough gold films, and sharp gold tips and demonstrate that the infrared signal is only present for surfaces with nanometer-scale roughness.

Atomic and laser spectroscopy

Abstract: 1. Introduction 2. Review of Classical Electrodynamics 3. Review of Quantum Mechanics 4. The Spontaneous Emission of Radiation 5. Selection Rules for Electric Dipole Transitions 6. Measurement of Radiative Lifetimes of Atoms and Molecules 7. Forbidden Transitions and Metastable Atoms 8. The Width and Shape of Spectral Lines 9. The Absorption and Stimulated Emission of Radiation 10. Radiative Transfer and the Formation of Spectral Lines 11. Population Inversion Mechanisms in Gas Lasers 12. Resonant Modes of Optical Cavities 13. Saturation Characteristics and the Single-Frequency Operation of Gas Lasers 14. Turnable Dye Lasers and Atomic Spectroscopy 15. The Hanle Effect and the Theory of Resonance Flourescence Experiments 16. Optical Double Resonance Experiments 17. Optical Pumping Experiments 18. The Hyperfine Structure of Atoms and its Investigation by Magnetic Resonance Methods Appendix

Demonstration of self-seeding in a hard-X-ray free-electron laser

Abstract: Lasing in a hard-X-ray free-electron laser is typically seeded from noise due to the self-amplification of spontaneous emission, which limits temporal coherence and spectral characteristics. Researchers now demonstrate self-seeding using X-rays from the first half of the magnetic undulator to seed the second half via a diamond-based monochromator at angstrom wavelengths.

Spontaneous emission near the edge of a photonic band gap

Abstract: We study spontaneous emission near the edge of a photonic band gap. Instead of a simple exponential decay in the vacuum, spontaneous emission displays an oscillatory behavior. A single photon-atom bound dressed state exhibits a fractional steady-state atomic population on the excited state. For a three-level atom we evaluate the spectral splitting and subnatural linewidth of spontaneous emission. In the presence of N-1 unexcited atoms we show that the collective time scale factor is equal to ${\mathit{N}}^{\mathrm{\ensuremath{\varphi}}}$, where \ensuremath{\varphi}=2/3 for an isotropic band gap and \ensuremath{\varphi}=1 or 2 for anisotropic two-dimensional or three-dimensional band edges, respectively.

Energy-transfer pumping of semiconductor nanocrystals using an epitaxial quantum well.

Abstract: As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size1,2. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies—for example, displays, fluorescence tagging3, solid-state lighting and lasers4. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals. Here, we describe an approach for indirect injection of electron–hole pairs (the electron–hole radiative recombination gives rise to light emission) into nanocrystals by non-contact, non-radiative energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically. Our theoretical and experimental results indicate that this transfer is fast enough to compete with electron–hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures. Furthermore, the measured energy-transfer rates are sufficiently large to provide pumping in the stimulated emission regime, indicating the feasibility of nanocrystal-based optical amplifiers and lasers based on this approach.