The use of techniques for analyzing the fluorescence photon statistics of a single molecule for modeling single-emitter dynamics is demonstrated. The photon distribution function measured in the fluorescence of a single tetra-tert-butylterrylene molecule embedded in polyisobutylene is used to devise a theoretical model for single emitters with complicated fluorescence photon statistics. Our analysis was carried out with the theoretical approach developed by Osad'ko and co-workers [J. Chem. Phys. 130, 064904 (2009); J. Phys. Chem. C 114, 10349 (2010)] for photon distribution functions. Although the experimental data were obtained at cryogenic temperature where narrow zero-phonon lines are present, the method is based on a purely statistical approach and does not require spectrally resolved data. It can also be applied to the analysis of broad fluorescence bands as measured at room temperature. Therefore, the method has prospects for revealing the quantum dynamics of single biological objects and other single quantum emitters in ambient conditions.
The use of techniques for analyzing the fluorescence photon statistics of a single molecule for modeling single-emitter dynamics is demonstrated. The photon distribution function measured in the fluorescence of a single tetra-tert-butylterrylene molecule embedded in polyisobutylene is used to devise a theoretical model for single emitters with complicated fluorescence photon statistics. Our analysis was carried out with the theoretical approach developed by Osad'ko and co-workers [J. Chem. Phys. 130, 064904 (2009); J. Phys. Chem. C 114, 10349 (2010)] for photon distribution functions. Although the experimental data were obtained at cryogenic temperature where narrow zero-phonon lines are present, the method is based on a purely statistical approach and does not require spectrally resolved data. It can also be applied to the analysis of broad fluorescence bands as measured at room temperature. Therefore, the method has prospects for revealing the quantum dynamics of single biological objects and other single quantum emitters in ambient conditions.
An analysis of intermittent fluorescence is presented for a single molecule driven by a continuous-wave laser field. The interruptions of fluorescence are caused by transition of the molecule to a triplet state. A method previously developed to calculate photon distribution for continuous-wave fluorescence is applied to analyze photon statistics of fluorescence blinking. The probability w N (T) of counting N photons over a time interval T is derived for intermittent fluorescence. The photons counted over relatively short intervals are found to have a sub-Poissonian (narrower than Poisson) distribution. The photon distribution over intervals longer than the mean off time has a complicated form with two maxima; i.e., a super-Poissonian (wider than Poisson) distribution is obtained.
Single-molecule fluorescence microscopy has been established in life science as an essential tool for studying the characteristics and dynamics of individual fluorescent emitters both in vitro as well as in vivo. Acquiring quantitative information from the confocal observation volume is still a challenging task and knowing the absolute number or concentration of proteins in, e.g., cellular structures can significantly improve our understanding of cell biology, which is an important step towards quantitative microscopy. In this talk, a new quantitative analytical tool called Counting by Photon Statistics (CoPS) will be presented. The approach relies on a statistical analysis of detected photon coincidences to estimate the number of independent fluorescent labels in the observation volume [1]. CoPS does exploit the photon antibunching effect: a single photon emitter can only generate one photon at a time. Originally developed for point measurements, CoPS has recently been extended to an imaging scheme [2]. Using a confocal fluorescence microscopy setup with pulsed excitation, four single-photon, detectors and parallellized time-correlated single photon counting electronics (MicroTime 200, PicoQuant), we prove the applicability of the method with artificial model systems (immobilized DNA origami) and present first steps towards biological samples. [1] Ta, H., Wolfrum, J., Herten, D.-P., An extended scheme for counting fluorescent molecules by photon-antibunching Laser Phys. 20:119 (2010). [2] Ta, H. et al., Mapping molecules in scanning far-field fluorescence nanoscopy. Nat. Commun. 6:7977 (2015).
The lack of reliable quantitative methods in fluorescence microscopy prevents the detailed investigation of basic molecular processes. Single-molecule fluorescence spectroscopy offers several techniques to determine the stoichiometry of fluorescent probes. Among them, an approach using the single-photon emission of an individual quantum system, also known as photon antibunching, yields access to both the emitter number and their molecular brightness. Previous work demonstrated the feasibility of the method to estimate up to five dyes without further physical characterization. In this work, I investigated and improved the reliability and robustness of this method. I developed different fluorescent probes with a defined label stoichiometry to explore the performance of our approach \nin experiments. I could demonstrate, in combination with simulations, that it can provide reliable estimates of up to 18 fluorescent emitters at a time resolution of approximately 200 ms. Furthermore, I inspected the dependency of the estimation bias and precision on the laser intensity, the analysis time and the number of expected molecules in detail. My results designate the scope for future stoichiometry determinations. In initial experiments, I analyzed the labeling distributions of different fluorescent probes. In addition, I could combine our counting approach with super-resolution STED-microscopy and identify critical parameters for possible applications
We extend the generating function technique for calculation of single molecule photon emission statistics (Zheng, Y.; Brown, F. L. H. Phys. Rev. Lett. 2003, 90, 238305) to systems governed by multi-level quantum dynamics. This opens up the possibility to study phenomena that are outside the realm of purely stochastic and mixed quantum-stochastic models. In particular, the present methodology allows for calculation of photon statistics that are spectrally resolved and subject to quantum coherence. Several model calculations illustrate the generality of the technique and highlight quantitative and qualitative differences between quantum mechanical models and related stochastic approximations when they arise. Calculations suggest that studying photon statistics as a function of photon frequency has the potential to reveal more about system dynamics than the usual broadband detection schemes.
The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of interphoton time distributions, second order correlation functions, and the variance of the photon number probability distribution. Antibunching at short times and bunching behavior for longer times is observed, associated with sub- and super-Poissonian statistics, respectively. A rate-equation analysis of the molecular level populations indicates an accelerated reverse intersystem crossing.
Single photons are highly desirable for encoding, sending and processing quantum information. Suitable engineering of single quantum emitters and their environment can lead to a reliable single photon source and to mediated photon-photon interactions, essential assets for quantum communication and computation purposes. Dye molecules, our chosen single quantum emitter, have attracted much attention in recent years due to their high photostability and narrow emission lines. In this thesis I present a detailed analysis of the optical properties of single dibenzoterrylene molecules in an anthracene matrix. Single photon emission is demonstrated at room and cryogenic temperatures. In the latter case, an analysis of the second-order correlation function of the emission of a single molecule is studied at various temperatures. The data agree with a full solution of the optical Bloch equations over a wide range of temperature, and provide some insight into the dephasing process of the molecules. I then present a technique for integrating single dye molecules with nano-photonic devices. These are hybrid plasmonic waveguides, designed to guide light and to enhance the interaction with a single emitter by a tight confinement of the waveguide mode. Single molecules are deposited over the waveguides and a first evidence of coupling is presented. I conclude with proposed improvements to the optical setup and to the deposition methods. Finally, I present another type of integrated device, where the light matter interaction is enhanced by inserting single quantum emitters into coupled optical resonators. The theoretical description for the case of resonant two-photon absorption from single atoms in coupled photonic crystal cavities is developed. I conclude by proposing a possible realisation of this system, and describing the first steps towards the fabrication of such a device.