KEYWORDS (Word Style "BG_Keywords"). If you are submitting your paper to a journal that requires keywords, provide significant keywords to aid the reader in literature retrieval.In this work, we present a novel technique to directly measure the phase shift of the optical signal scattered by single plasmonic nanoparticles in a diffraction-limited laser focus. We accomplish this by equipping an inverted confocal microscope with a Michelson interferometer and scanning single nanoparticles through the focal volume while recording interferograms of the scattered and a reference wave for each pixel. For the experiments, lithographically prepared gold nanorods where used, since their plasmon resonances can be controlled via their aspect ratio. We have developed a theoretical model for image formation in confocal scattering microscopy for nanoparticles considerably smaller than the diffraction limited focus We show that the phase shift observed for particles with different longitudinal particle plasmon resonances can be well explained by the harmonic oscillator model. The direct measurement of the phase shift can further improve the understanding of the elastic scattering of individual gold nanoparticles with respect to their plasmonic properties.

Optical half-wave microresonators enable to control the optical mode density around a quantum system and thus to modify the temporal emission properties. If the coupling rate exceeds the damping rate, strong coupling between a microresonator and a quantum system can be achieved, leading to a coherent energy exchange and the creation of new hybrid modes. Here, we investigate strong coupling between two adjacent /2 Fabry-Pérot microresonators, where the resonance of one microresonator can be actively tuned across the resonance of the other microresonator. The transmission spectra of the coupled microresonators show a clear anticrossing behavior, which proves that the two cavity modes are strongly coupled. Additionally, we can vary the coupling rate by changing the resonator geometry and thereby investigate the basic principles of strong coupling with a well-defined model system. Finally, we will show that such a coupled system can theoretically be modelled by coupled damped harmonic oscillators.Optical /2 microresonators are structures that confine light to volumes with dimensions on the order of a wavelength and enable to control and study light-matter interaction. The interaction between a quantum system and an optical field confined in a microresonator can be divided into the weak and strong coupling regime. In the weak coupling regime, the respective decay rates are larger than the coupling rate between the quantum system and the microresonator. In this case, the spontaneous emission rate of the quantum system is altered with respect to the free space, a phenomenon known as Purcell effect [1]. To reach the strong coupling regime, the coupling strength between the optical field in the resonator and the quantum system must be considerably larger than their respective decay rates. This leads to new hybrid polaritonic states [2], which have an energy difference proportional to the coupling strength. The spectral signature is a splitting of the absorption or transmission spectrum into two polaritonic modes, referred to as Rabi splitting [3]. When the cavity resonance is tuned over the eigenfrequency of the quantum system, anticrossing is observed in the dispersive behavior of the polaritonic modes [4]. The first observation of strong coupling between electromagnetic fields and a quantum system has been shown in the form of interaction between Rydberg atoms and a high Q microwave cavity at cryogenic temperatures [5]. Since then, many different optical experiments showing strong light matter coupling have been accomplished using metal or dielectric cavities [4,6-11], photonic crystals [12], micropillars [13] or microdisks [14] that couple with quantum dots [12][13][14], organic semiconductors [15] or J-aggregates [16]. Strong coupling has been shown for molecular systems from ensembles down to single molecules that couple to cavity fields, as well as to plasmonic modes [17][18][19] with sub wavelength dimensions. Today, strong coupling with plasmonic modes at ambient conditions has been shown even for single molecules...

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During photosynthesis, energy conversion at the two photosystems is controlled by highly complex and dynamic adaptation processes triggered by external factors such as light quality, intensity, and duration, or internal cues such as carbon availability. These dynamics have remained largely concealed so far, because current analytical techniques are based on the investigation of isolated chloroplasts lacking full adaptation ability and are performed at non-physiologically low temperatures. Here, we use non-invasive in planta spectro-microscopic approaches to investigate living chloroplasts in their native environment at ambient temperatures. This is a valuable approach to study the complex function of these systems, because an intrinsic property—the fluorescence emission—is exploited and no additional external perturbations are introduced. Our analysis demonstrates a dynamic adjustment of not only the photosystemI/photosystemII (PSI/PSII) intensity ratio in the chloroplasts but also of the capacity of the LHCs for energy transfer in response to environmental and internal cues.