We present for the first time cavity‐controlled fluorescence spectra and decay curves of single dipole emitters interacting at room temperature with the first longitudinal mode of a Fabry–Perot ...microcavity offering a λ/2‐spacing between its silver mirrors. The spontaneous emission rate of individual dye molecules was found to be enhanced by the Purcell effect by up to three times compared to the rate in free space, in agreement with theoretical predictions. Moreover, our new microcavity design was found to provide long‐term stability and single‐molecule sensitivity under ambient conditions for several months without noticeable reduction of the cavity‐Q value. We consider this as a significant advance for single‐photon sources operating at room temperature.
Tailoring single‐molecule fluorescence: The fluorescence characteristics of single immobilized dye molecules are controlled by the interaction with a λ/2 Fabry–Perot‐type microcavity (see picture). The microcavity design can be integrated on a microchip to act as a tunable single‐photon source or as an ultrasensitive microfluidic analytical device.
We have investigated the influence of the plasmon resonances of individual, spatially isolated gold nanoparticle aggregates on their emission properties using combined optical confocal and dark field ...scattering microscopy and spectroscopy. The emission intensity of the same aggregate is enhanced by up to 1 order of magnitude if the emission wavelengths overlap with the plasmon resonance in the corresponding white light scattering spectrum. Regardless of the specific geometry of an individual aggregate, the in situ measurement of the plasmon characteristics delivers unique information about its potential as a substrate for surface-enhanced spectroscopy and allows its characterization as a nanoscatterer, nanoemitter, or local heater.
Silicon nanocrystals were synthesized by CO2 laser pyrolysis of SiH4. The fresh silicon nanopowder was oxidized in water to obtain SiO2 nanoparticles (NPs) exhibiting strong red-orange ...photoluminescence. Samples of SiO2 NPs embedded in low concentration in a thin polymer layer were prepared by spin-coating a dedicated solution on quartz cover slides. Using an argon ion laser at 488 nm with higher-order laser modes (azimuthally and radially polarized doughnut modes) for excitation, the three-dimensional orientation of the nanoparticles’ transition dipole moment was investigated in a confocal microscope. The linear transition dipole moment was found to be rather stable and randomly oriented. However, dynamical effects such as fluorescence intermittency and transition dipole moment flipping could also be observed. The spectral analysis of single SiO2 NPs revealed double-peak spectra consisting of a narrow zero-phonon line and a broader phonon band being associated with the excitation of longitudinal optical phonons in the SiO2 NP.
We present a novel scattering microscopy method to detect the orientation of individual silver nanorods and to measure their relative distances. Using confocal microscopy in combination with either ...the fundamental or higher order laser modes, scattering images of silver nanorods were recorded. The distance between two individual nanorods was measured with an accuracy in the order of 1 nm.We detected the orientation of isolated silver nanorods with a precision of 0.5 degree that corresponds to a rotational arch of about 1 nm. The results demonstrate the potential of the technique for the visualization of non-bleaching labels in biosciences.
We analyzed the scattering patterns of individual Au nanorods detected by means of confocal interference scattering microscopy in combination with a higher order laser mode. We placed the Au nanorods ...at the interface between two dielectric media and examined the influence of different interfaces on the signal amplitude, the signal-to-noise ratio as well as on the precision of topological measurements. Approaching the index matching regime allows for topological measurements with high accuracy minimizing the acquisition time. We were also able to track the position and the orientation of particles embedded in water even when they were not thoroughly sticking to the glass surface. These results underscore the potential of the presented technique for applications in life sciences.
We studied spatially isolated single-walled carbon nanotubes (SWNTs) immobilized in a quasi-planar optical λ/2-microresonator using confocal microscopy and spectroscopy. The modified photonic mode ...density within the resonator is used to selectively enhance or inhibit different Raman transitions of SWNTs. Experimental spectra are presented that exhibit single Raman bands only. Calculations of the relative change in the Raman scattering cross sections underline the potential of our microresonator for the optical control of nonequilibrium phonon populations in SWNT.
The cover picture shows
a dipole emitter embedded in a microresonator with variable mirror separation that is excited by a tightly focused laser beam. Single dye molecules can be forced to emit into ...a narrow spectral window with an enhanced fluorescence rate (red curve). The efficiency of this process is determined by the interplay between the microresonator structure and the original fluorescence spectrum of the dye (grey curve). Details can be found in the Article by M. Steiner et al. on page 2190.
We studied spatially isolated single-walled carbon nanotubes (SWNTs) immobilized in a quasi-planar optical λ/2-microresonator using confocal microscopy and spectroscopy. The modified photonic mode ...density within the resonator is used to selectively enhance or inhibit different Raman transitions of SWNTs. Experimental spectra are presented that exhibit single Raman bands only. Calculations of the relative change in the Raman scattering cross sections underline the potential of our microresonator for the optical control of nonequilibrium phonon populations in SWNT.
PDF
