A dual-color super-resolution microscope with polarization and orientation-resolving capabilities is presented. Combining single-molecule localization methods with simultaneous polarization measurements enables the determination of the orientation of single emitters, such as quantum dot nanocrystals, with sub-10 nm precision. Additional simultaneous spectral characterization of particle emission allows the capture of multiple optical properties that impact energy transfer. We report on the instrumentation development and the results from coupled quantum dot clusters.
KEYWORDS: Sensors, Point spread functions, Monte Carlo methods, Optical fibers, Avalanche photodetectors, Avalanche photodiodes, Luminescence, Molecules, Time correlated photon counting, Super resolution microscopy, Fluorescence lifetime imaging, Single photon detectors, Single molecule spectroscopy, Quantum dots
Photoluminescence images can be acquired with detection schemes that have both single-photon sensitivity and nanosecond scale temporal resolution, enabling the study of possible structural bases for photoluminescence lifetimes and other features of the photon arrival statistics. Within the context of super-resolution (SR) imaging, this has been demonstrated with detection schemes that collect images with a bundle of optical fibers that are coupled to individual single-photon counting avalanche photodiode detectors. Recently, our group used a bundle of four optical fibers to collect these “time-resolved photon arrival” images. Despite the paucity of information contained in a four-pixel image, we precisely located the emission centroid of quantum dots (QDs) and observed correlations between centroid location, photoluminescence lifetime, and intensity within clusters of QDs that were suggestive of electronic interactions among them. This proceedings paper details the approach that we used to locate the emission centroid based on the counts in the four detectors.
Semiconductor quantum dots (QDs) in small clusters can exchange excited state energy via various transfer mechanisms such as F¨orster resonant energy transfer (FRET). Such energy transfer enables excitons to move from larger bandgap donors to smaller bandgap acceptors. Clusters of mixed donor/acceptor QD species consequently have a spectral signature that is dependent on which QDs in the clusters are responsible for the emission. Using a dual-color super-resolution imaging approach, we report on the spectral characteristics of interacting QDs in clusters with nanometer spatial resolution. Higher emission intensities from clusters are shown to emanate from sub-regions of the clusters and have spectral signatures that indicate the emission is dominated by the acceptor region of the spectrum. Thus, energy transferring interactions among QDs in clusters funnel excitons primarily to acceptor particles. Acceptor particles are responsible for the majority of the emission from the clusters with an emission spectra corresponding to the spectral profiles of the acceptor species.
Quantum light and in particular single photons have become essential resources for a growing number of quantum applications including quantum computing, quantum key distribution and quantum metrology. Solid-state atomlike systems such as semiconductor quantum dots and color defects in crystals have become the hallmark of highly pure single photon emitters in the past two decades. A particular interest has been developed in nanocrystal quantum dots (NQDs) and color centers in diamond as potential compact room-temperature emitters. There are however several challenges that inhibit the use of such sources in current technologies including low photon extraction efficiency, low emission rates and relatively low single photon purities. In this work we will review our efforts in overcoming these technical difficulties using several complementary methods including designing several nanoantenna devices that enhance the directionality and emission rate of the nanoemitter. In addition, we developed several temporal heralding techniques to overcome the hurdle of low single photon purity in NQDs in an effort to produce a highly pure, bright and efficient single photon source on-chip.
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