215 research outputs found
Rotational Correlation Functions of Single Molecules
Single molecule rotational correlation functions are analyzed for several
reorientation geometries. Even for the simplest model of isotropic rotational
diffusion our findings predict non-exponential correlation functions to be
observed by polarization sensitive single molecule fluorescence microscopy.
This may have a deep impact on interpreting the results of molecular
reorientation measurements in heterogeneous environments.Comment: 5 pages, 4 figure
The intensity correlation function of "blinking" quantum systems
Explicit expressions are determined for the photon correlation function of
``blinking'' quantum systems, i.e. systems with different types of fluorescent
periods. These expressions can be used for a fit to experimental data and for
obtaining system parameters therefrom. For two dipole-dipole interacting
systems the dependence on the dipole coupling constant is explicitly given and
shown to be particularly pronounced if the strong driving is reduced. We
propose to use this for an experimental verification of the dipole-dipole
interaction.Comment: 12 pages, 5 figures, uses iopams.st
Photon antibunching in the fluorescence of individual color centers in diamond
We have observed photon antibunching in the fluorescence light emitted from a
single N-V center in diamond at room temperature. The possibility of generating
triggerable single photons with such a solide state system is discussedComment: 4 pages, 4 figure
Detection of Single Molecules Illuminated by a Light-Emitting Diode
Optical detection and spectroscopy of single molecules has become an
indispensable tool in biological imaging and sensing. Its success is based on
fluorescence of organic dye molecules under carefully engineered laser
illumination. In this paper we demonstrate optical detection of single
molecules on a wide-field microscope with an illumination based on a
commercially available, green light-emitting diode. The results are directly
compared with laser illumination in the same experimental configuration. The
setup and the limiting factors, such as light transfer to the sample, spectral
filtering and the resulting signal-to-noise ratio are discussed. A theoretical
and an experimental approach to estimate these parameters are presented. The
results can be adapted to other single emitter and illumination schemes.Comment: 7 pages, 5 figure
Photonic mode density effects on single-molecule fluorescence blinking
We investigated the influence of the photonic mode density (PMD) on the
triplet dynamics of individual chromophores on a dielectric interface by
comparing their response in the presence and absence of a nearby gold film.
Lifetimes of the excited singlet state were evaluated in ordet to measure
directly the PMD at the molecules position. Triplet state lifetimes were
simultaneously determined by statistical analysis of the detection time of the
fluorescence photons. The observed singlet decay rates are in agreement with
the predicted PMD for molecules with different orientations. The triplet decay
rate is modified in a fashion correlated to the singlet decay rate. These
results show that PMD engineering can lead to an important suppression of the
fluorescence, introducing a novel aspect of the physical mechanism to enhance
fluorescence intensity in PMD-enhancing systems such as plasmonic devices
Enhancing single-molecule photostability by optical feedback from quantum-jump detection
We report an optical technique that yields an enhancement of single-molecule
photostability, by greatly suppressing photobleaching pathways which involve
photoexcitation from the triplet state. This is accomplished by dynamically
switching off the excitation laser when a quantum-jump of the molecule to the
triplet state is optically detected. This procedure leads to a lengthened
single-molecule observation time and an increased total number of detected
photons. The resulting improvement in photostability unambiguously confirms the
importance of photoexcitation from the triplet state in photobleaching
dynamics, and may allow the investigation of new phenomena at the
single-molecule level
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