Revealing single emitter spectral dynamics from intensity correlations in an ensemble fluorescence spectrum

We show that the single emitter linewidth underlying a broadened ensemble emission spectrum can be extracted from correlations among the stochastic intensity fluctuations in the ensemble spectrum. Spectral correlations can be observed at high temporal and spectral resolutions with a cross-correlated pair of avalanche photodiodes placed at the outputs of a scanning Michelson interferometer. As illustrated with simulations in conjunction with Fluorescence Correlation Spectroscopy, our approach overcomes ensemble and temporal inhomogeneous broadening to provide single emitter linewidths, even for emitters under weak, continuous, broadband excitation.Comment: 9 pages, 5 figure

Synthese von Coil-Rod-Coil-Blockcopolymeren und Synthese "haariger" MOFs

Brokmann L. Synthese von Coil-Rod-Coil-Blockcopolymeren und Synthese "haariger" MOFs. Bielefeld: Universität Bielefeld; 2019

Determination of piezo-resistive coefficient π44 in p-type silicon by comparing simulation and measurement of pressure sensors

The piezo-resistive coefficient π44 is reported for the case of single crystalline p-type silicon. By comparing the measured sensitivity of pressure sensors with the simulated sensitivity of these pressure sensors, we are able to extract π44 since this is the only free parameter in the simulation. A value of π44 = (108.3 ± 2.1) × 10−11 Pa−1 at a dopant concentration of (5.0 ± 4.5) × 1017 cm−3 was found, which is in good agreement with experimental literature dat

Beitrag zur Mikrostrukturierung von fotostrukturierbarem Glas mittels UV-Laserstrahlung

Abstract The rationale of this PhD dissertation is the systematic elaboration of interaction parameters of UV-laser radiation with photosensitive glass. Photochemical modifications in the photo-sensitive glass can be used for geometrical micro structurization processes using UV-laser radiation. A directly writing-exposure-method is used to perform irradiations. All parameters concerning exposure and micro structurization processes are systematically investigated and discussed. A short introduction includes all necessary information concerning the used glasses, exposure processes and micro structurization outlines basically required for further understanding of the topics. Subsequent sections describe the characterization of the used photosensitive glass prior to exposure. The photo form process consisting of: 1st: UV-laser exposure by 3 different laser types (3??Nd:YAG solid-state laser, XeCl- and KrF-excimer laser), 2nd: thermally induced partial crystallization in exposed areas, and 3rd: dissolution of partially crystallized by wet chemical etching processes is systematically investigated in respect to exposure and other process determining parameters. The fundamental progress in knowledge is given by the description of radiation induced modifications in photo structurable glass to optical properties and consequential structure modifications in partial crystallized areas of thermal treated samples. Samples were investigated with UV-VIS spectrometry, REM, TEM- and HREM, AFM as well as optical microscopic techniques. Regarding the irradiation process, four major processes were identified to be the most likely pathways for the formation of color centers: formation of (Ce3+)+ excitons, stimulated states of polyvalent elements (Sb, Sn), non-bridging-oxygens and formation of silver-nano-clusters inside the glass matrix. Irradiated samples crystallized during a subsequent thermal treatment were investigated in respect to their crystallized areas (crystallization depth, lateral geometry, crystal size and crystal network). After the final photo structurization step (etching), etch rate ratios were determined in dependence of exposure parameters. Results in the present study and potential fields of application for the systematically investigated photo structurization process are briefly discussed.Wird ein fotosensibles Glas mit UV-Laserstrahlung belichtet, so können fotochemische Gefügemodifizierungen im Glas für einen geometrischen Mikrostrukturierungsprozess nach dem Fotoformverfahren genutzt werden. Für ein verbessertes Prozessverständnis erfolgt anhand einer direkt-schreibenden Belichtungsmethode die systematische Untersuchung des Einflusses von Belichtungsparametern auf Kenngrößen des Mikrostrukturierungsprozesses . Nach einer kurzen Einführung erfolgt die Darstellung der zum Verständnis notwendigen Grundlagen zum Fotoformverfahren, zur UV-Laser-Belichtung und zum verwendeten fotostrukturierbaren Glas. Der Hauptteil der Arbeit widmet sich der Analyse des Einflusses der Belichtungsparameter auf die 3 Prozessschritte des Fotoformverfahrens: UV-Laser-Belichtung (KrF- und XeCl-Excimerlaserstrahlung und (3w)Nd:YAG Festkörperlaserstrahlung), partielle Kristallisation durch Temperung und geometrische Mikrostrukturierung durch nasschemisches Ätzen. Der grundlegende Erkenntnisfortschritt besteht in der Beschreibung strahlungsinduzierter Gefügemodifizierungen auf optische Eigenschaften des Glases und den daraus folgenden Strukturveränderungen in partiell kristallisierten Bereichen getemperter Proben. UV-Laser-belichtete Proben wurden mittels UV-VIS-Spektroskopie, TEM-, HREM-, REM- und AFM-Analyse sowie optischer Lichtmikroskopie untersucht. Die wesentlichen Ergebnisse sind: infolge UV-Laser-Belichtung erfolgt die Bildung von angeregten Zuständen an Ce3+-Ionen, Farbzentren an polyvalenten Elementen (Zinn, Antimon) und Trennstellensauerstoffen sowie Ag-Nanopartikel im Glas. Aus der Belichtung resultierende Gefügemodifizierungen beeinflussen die Größe einzelner Kristalle und deren Vernetzung, die Kristallisationstiefe und die laterale Ausdehnung kristallisierter Bereiche. Das Ätzratenverhältnis wird maßgeblich vom Grad der Vernetzung der einzelnen Kristalle bestimmt. In einem abschließenden Kapitel wird der Einfluss von Belichtungsparametern auf die Glasmikrostrukturierung anhand strukturierter Gräben für die Belichtung mit XeCl-Excimerlaserstrahlung diskutiert. Die potentiellen Anwendungsfelder für das vorgestellte Verfahren liegen auf den Gebieten der Mikrosensorik, -aktuatorik, -mechanik, -optik, -fluidtechnik und nicht zuletzt der Mikroreaktionstechni

UV laser radiation for microstructuring of photostructurable glasses

Photostructurable glasses are important materials for applications in microsystems. They enable structures with high aspect ratios and a high dependability of mechanical, optical and chemical properties in a large range of temperatures. The exposure of photostructurable glasses to UV laser radiation, as a rapid prototyping technique, is an alternative method to the exposure by a mask aligner. Α photostructurable glass (FS21) was exposed to UV laser radiation of the wavelengths 248, 308 and 355 nm. Investigated was the influenee of the exposure parameters wavelength of laser radiation and energy density on structuring results such as crystallization depth, lateral geometry of crystallized areas, structure of crystallized areas and etch angle for single pulse exposure

Evidence for a diffusion-controlled mechanism for fluorescence blinking of colloidal quantum dots

Fluorescence blinking in nanocrystal quantum dots is known to exhibit power-law dynamics, and several different mechanisms have been proposed to explain this behavior. We have extended the measurement of quantum-dot blinking by characterizing fluctuations in the fluorescence of single dots over time scales from microseconds to seconds. The power spectral density of these fluctuations indicates a change in the power-law statistics that occurs at a time scale of several milliseconds, providing an important constraint on possible mechanisms for the blinking. In particular, the observations are consistent with the predictions of models wherein blinking is controlled by diffusion of the energies of electron or hole trap states

Aging in Financial Market

We analyze the data of the Italian and U.S. futures on the stock markets and we test the validity of the Continuous Time Random Walk assumption for the survival probability of the returns time series via a renewal aging experiment. We also study the survival probability of returns sign and apply a coarse graining procedure to reveal the renewal aspects of the process underlying its dynamics.Comment: To appear in special issue of Chaos, Solitons and Fractal