Spontaneous emission

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

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

Abstract: We study experimentally time-resolved emission of colloidal CdSe quantum dots in an environment with a controlled local density of states (LDOS). The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. We manage to obtain the oscillator strength of the important class of CdSe quantum dots. The oscillator strength varies weakly with frequency in agreement with behavior of quantum dots in the strong confinement limit. Surprisingly, previously calculated tight-binding results differ by a factor of 5 with the measured absolute values. Results from pseudopotential calculations agree well with the measured radiative rates. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics

Fluorescence control through multiple interference mechanisms

Abstract: We discuss the spontaneous emission from a coherently prepared and microwave-driven doublet of potentially closely spaced excited states to a common ground level. Multiple interference mechanisms are identified that may lead to fluorescence inhibition in well-separated regions of the spectrum or act jointly in canceling the spontaneous emission. In addition to phase-independent quantum interferences due to combined absorptions and emissions of driving field photons, we distinguish two competing phase-dependent interference mechanisms as means of controlling the fluorescence. The indistinguishable quantum paths may involve the spontaneous emission from the same state of the doublet, originating from the two different components of the initial coherent superposition. Alternatively the paths involve a different spontaneous photon from each of two decaying states, necessarily with the same polarization. This makes these photons indistinguishable in principle within the uncertainty of the two decay rates. The phase dependence arises for both mechanisms because the interfering paths differ by an unequal number of stimulated absorptions and emissions of the microwave field photons. @S1050-2947~98!03011-X#

Structure in the nonlinear saturation spectrum of parametric instabilities

Abstract: The nonlinear saturation spectrum of the decay instability is obtained in the limit of small spontaneous emission, for comparable ion and electron temperatures, from numerical solutions of a kinetic equation based on an accurate expression for the nonlinearity. The spectral energy occupies several pairs of isolated saucer‐shaped regions in wave‐vector space. The regions increase in thickness, angular diameter, and number as the pump power is increased. The theory thus predicts the generation of waves propagating in directions which can differ substantially from the direction of the pump field. Ionospheric observations confirm this prediction; they were difficult to reconcile with the predictions of previous theories based on an approximate expression for the nonlinearity. The present work also corrects the results of previous one‐dimensional theories that used an accurate expression for the nonlinearity and predicted “spectral lines” in the limit of vanishing spontaneous emission. Excitation of the purely growing instability is predicted for pump powers greater than about 2.5 times the threshold of the decay instability.

High-brightness single photon source from a quantum dot in a directional-emission nanocavity

Abstract: We analyze a single photon source consisting of an InAs quantum dot coupled to a directional-emission photonic crystal (PC) cavity implemented in GaAs. On resonance, the dot’s lifetime is reduced by more than 10 times, to 45ps. Compared to the standard three-hole defect cavity, the perturbed PC cavity design improves the collection efficiency into an objective lens (NA = 0.75) by factor 4.5, and improves the coupling efficiency of the collected light into a single mode fiber by factor 1.9. The emission frequency is determined by the cavity mode, which is antibunched to g^(2)(0) = 0.05. The cavity design also enables efficient coupling to a higher-order cavity mode for local optical excitation of cavity-coupled quantum dots.

A condition of single longitudinal mode operation in injection lasers with index-guiding structure

Abstract: A condition for single longitudinal mode operation (SMO, for short) of index-guided injection lasers is given theoretically and supported by experiment. For SMO, the transverse higher modes must be cut off by using a narrow-width index-guiding waveguide. Inclusion of the spontaneous emission into the lasing field must be reduced by using a thinner active region. In terms of the impurity concentration of the active region, the undoped case is the most stable for temperature variation. A heavily doped active region may also produce SMO. The thermal resistance must be reduced to increase temperature stability. MO with a fixed lasing wavelength is experimentally obtained by temperature control up to an injection current of twice threshold.