Inst. Optik und Atomare Physik

178 Items

Recent Submissions
Computational imaging methods for visible light and X-ray microscopy

Lötgering, Lars (2020)

In this thesis two computational imaging techniques, namely ptychographic coherent diffraction imaging and propagation-based phase retrieval, are explored. Central to both techniques are algorithmic aspects which are formulated in the framework of nonlinear optimization. Applications such as optical phase retrieval, x-ray beam characterization and lensless imaging are discussed both in theory a...

Symmetric cladding thin-film waveguides

Pufahl, Karsten Simon (2020)

Intrinsic absorption is often considered an undesirable effect in waveguiding applications, severely limiting the propagation length. However, with appropriate design of a symmetric cladding, waveguiding can be achieved even with highly absorbing media, to the degree that increasing absorption has a positive effect on the propagation length. Here, this counterintuitive concept is developed furt...

Two-photon based pulse autocorrelation with CdSe nanoplatelets

Quick, Michael T. ; Owschimikow, Nina ; Khan, Ali Hossain ; Polovitsyn, Anatolii ; Moreels, Iwan ; Woggon, Ulrike ; Achtstein, Alexander W. (2019-09-06)

We investigate broadband two-photon absorption autocorrelators based on II–VI semiconductor nanoplatelets as an alternative to common second harmonic generation based techniques. As compared to bulk materials the exceptionally high enhancement of two-photon absorption in these 2D structures results in very efficient two-photon absorption based autocorrelation detected via PL emission. We compar...

Intracluster proton transfer in protonated benzonitrile–(H2O)n≤6 nanoclusters: hydrated hydronium core for n ≥ 2

Chatterjee, Kuntal ; Dopfer, Otto (2019-10-31)

Protonation and hydration of aromatic hydrocarbon molecules and their derivatives play a key role in many biological and chemical processes. The recent detection of benzonitrile (BN, cyanobenzene, C6H5CN) in the interstellar medium suggests the existence of its protonated form (H+BN) in both the gas phase and in or on ice grains. Herein, we analyze the vibrational signatures of size-selected pr...

Submonolayer-grown quantum dots for nonlinear device applications

Herzog, Bastian (2019)

The submonolayer (SML) growth method was developed as an alternative to the established Stranski-Krastanow (SK) technique in order to produce quantum dots (QDs) with higher areal density and consequently larger optical gain. In this dissertation, fundamental and applied aspects of SML-grown QDs as active media in optoelectronic devices are investigated using different optical spectroscopy metho...

Manganese L-edge spectroscopy of the photosystem II protein and metal complexes in solution

Kubin, Markus (2019)

Photosynthetic water splitting is catalyzed at a Mn4CaO5 complex in the photosystem II protein (PS II). A fundamental understanding of this reduction-oxidation reaction requires detailed information on the electronic structure of the Mn4CaO5 complex and its changes during the water splitting reaction. Important properties of this electronic structure, relevant for a mechanistic understanding of...

Exploiting Nonlinear Photoacoustic Signal Generation in Gold Nanospheres for Selective Detection in Serial 3D PA Tomography

Schrof, Susanne ; Pang, Genny ; Buchmann, Jens ; Laufer, Jan (2018-12-08)

The photoacoustic (PA) signal amplitude measured in gold nanosphere suspensions has been shown to increase nonlinearly with the incident excitation fluence. In this work, this effect is exploited to recover the spatial distribution of gold nanoparticles in tomographic 3D photoacoustic (PA) images against the background contrast provided by absorbers that exhibit a linear relationship between th...

Microhydration Structures of Protonated Oxazole

Chatterjee, Kuntal ; Dopfer, Otto (2019-08-22)

The initial microhydration structures of the protonated pharmaceutical building block oxazole (Ox), H+Ox-Wn≤4, are determined by infrared photodissociation (IRPD) spectroscopy combined with quantum chemical dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ). Protonation of Ox, achieved by chemical ionization in a H2-containing plasma, occurs at the most basic N a...

Synergy Effect of Combining Fluorescence and Mid Infrared Fiber Spectroscopy for Kidney Tumor Diagnostics

Bogomolov, Andrey ; Belikova, Valeria ; Zabarylo, Urszula ; Bibikova, Olga ; Usenov, Iskander ; Sakharova, Tatiana ; Krause, Hans ; Minet, Olaf ; Feliksberger, Elena ; Artyushenko, Viacheslav (2017-11-05)

Matching pairs of tumor and non-tumor kidney tissue samples of four patients were investigated ex vivo using a combination of two methods, attenuated total reflection mid infrared spectroscopy and fluorescence spectroscopy, through respectively prepared and adjusted fiber probes. In order to increase the data information content, the measurements on tissue samples in both methods were performed...

Sea Silk

Pasche, Delphine (2019)

Nature offers excellent archetypes for the development of next generation polymeric materials, which combine exemplary performance with sustainable production. Indeed, many natural protein materials, including mussel anchoring fibers (byssus) exhibit very interesting combination of properties: high extensibility, high toughness and even self-healing capacity. The byssus research has focused pri...

Development and Testing of an LED-Based Near-Infrared Sensor for Human Kidney Tumor Diagnostics

Bogomolov, Andrey ; Zabarylo, Urszula ; Kirsanov, Dmitry ; Belikova, Valeria ; Ageev, Vladimir ; Usenov, Iskander ; Galyanin, Vladislav ; Minet, Olaf ; Sakharova, Tatiana ; Danielyan, Georgy ; Feliksberger, Elena ; Artyushenko, Viacheslav (2017-08-19)

Optical spectroscopy is increasingly used for cancer diagnostics. Tumor detection feasibility in human kidney samples using mid- and near-infrared (NIR) spectroscopy, fluorescence spectroscopy, and Raman spectroscopy has been reported (Artyushenko et al., Spectral fiber sensors for cancer diagnostics in vitro. In Proceedings of the European Conference on Biomedical Optics, Munich, Germany, 21–2...

Unraveling the protonation site of oxazole and solvation with hydrophobic ligands by infrared photodissociation spectroscopy

Chatterjee, Kuntal ; Dopfer, Otto (2019-01-19)

Protonation and solvation of heterocyclic aromatic building blocks control the structure and function of many biological macromolecules. Herein the infrared photodissociation (IRPD) spectra of protonated oxazole (H+Ox) microsolvated by nonpolar and quadrupolar ligands, H+Ox-Ln with L = Ar (n = 1–2) and L = N2 (n = 1–4), are analyzed by density functional theory calculations at the dispersion-co...

Thickening of T1 Precipitates during Aging of a High Purity Al−4Cu−1Li−0.25Mn Alloy

Häusler, Ines ; Kamachali, Reza Darvishi ; Hetaba, Walid ; Skrotzki, Birgit (2018-12-21)

The age hardening response of a high-purity Al–4Cu–1Li–0.25Mn alloy (wt. %) during isothermal aging without and with an applied external load was investigated. Plate shaped nanometer size T1 (Al2CuLi) and θ′ (Al2Cu) hardening phases were formed. The precipitates were analyzed with respect to the development of their structure, size, number density, volume fraction and associated transformation ...

Size-dependent exciton substructure in CdSe nanoplatelets and its relation to photoluminescence dynamics

Specht, Judith F. ; Scott, Riccardo ; Castro, Marta Corona ; Christodoulou, Sotirios ; Bertrand, Guillaume H. V. ; Prudnikau, Anatol V. ; Antanovich, Artsiom ; Siebbeles, Laurens D. A. ; Owschimikow, Nina ; Moreels, Iwan ; Artemyev, Mikhail ; Woggon, Ulrike ; Achtstein, Alexander W. ; Richter, Marten (2019-06-12)

CdSe nanoplatelets can be synthesized with different lateral sizes; very small nanoplatelets have almost quantum dot like features (almost discrete exciton states), while very large ones are expected to have properties of colloidal quantum wells (exciton continuum). However, nanoplatelets can be in an intermediate confinement regime with a rich substructure of excitons, which is neither quantum...

Untersuchung der Expansionsdynamik einzelner Xenoncluster induziert durch hochintensive Lichtpulse aus dem Infrarot- und weichen Röntgenbereich

Richter, Maria (2019)

Diese Arbeit beschäftigt sich mit den grundlegenden Prozessen, die hochintensive und kurze Lichtpulse in Nanopartikeln auslösen. Als Modellsystem werden Xenoncluster im Größenbereich von 20 bis 90\,nm im Radius verwendet. Es wird sowohl die Wechselwirkung von Clustern mit kurzwelligen Pulsen eines Freie-Elektronen-Lasers als auch mit Pulsen aus dem nahen Infrarotbereich (NIR) untersucht. Um dar...

Laboratory based GIXRF and GEXRF spectrometers for multilayer structure investigations

Szwedowski-Rammert, Veronika ; Baumann, Jonas ; Schlesiger, Christopher ; Waldschläger, Ulrich ; Gross, Armin ; Kanngießer, Birgit ; Mantouvalou, Ioanna (2019-02-11)

This work reports laboratory angle resolved measurements with the goal of establishing laboratory techniques to obtain a more complete idea of the intralayer composition of multilayer samples. While X-ray reflectometry is a widely available technique for the characterization of multilayer samples, angle resolved XRF measurements (grazing emission/incidence X-ray fluorescence) are usually perfor...

Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+lumiflavin complexes (M = Li–Cs)

Müller, David ; Nieto, Pablo ; Miyazaki, Mitsuhiko ; Dopfer, Otto (2019-01-07)

Flavin compounds are frequently used by nature in photochemical processes because of their unique optical properties which can be strongly modulated by the surrounding environment such as solvation or coordination with metal ions. Herein, we employ vibronic photodissociation spectroscopy of cryogenic M+LF complexes composed of lumiflavin (LF, C13H12N4O2), the parent molecule of the flavin famil...

Broadband ultrafast spectroscopy on mixed–dimensional InAs/GaAs systems

Kolarczik, Mirco (2019)

This thesis deals with light matter interaction and electron dynamics in coupled systems of nanostructured III-V semiconductors, particularly with quantum dots embedded in quantum wells. Its focus is on the role of dimensionality and the characterization of quantum dot states with respect to their two- and many-level nature. The sample under investigation is a semiconductor optical amplifier un...

New approaches in angle resolved X-ray analysis of stratified materials in the laboratory

Szwedowski-Rammert, Veronika (2019)

Providing access to angular resolved X-ray fluorescence methods in laboratories can enhance the dissemination of these methods for the depth-resolved elemental analysis of samples with layers in the nanometer range. The measurements are so far mainly performed at synchrotron radiation facilities and thus the number of users is limited. Especially in the hard X-ray range, where the production of...

Megaelectron volt secondary-ion mass spectrometry – yield dependence on experimental parameters and new capabilities of the technique

Stoytschew, Valentin (2019)

Time of flight Mega-electron Secondary Ion Mass Spectroscopy (TOF MeV SIMS) is a mass spectrometry technique using swift heavy ions (𝑚>16 𝑢, 𝐸𝑘𝑖𝑛>1 𝑀𝑒𝑉) to induce desorption of secondary ions from a sample. While swift heavy ions have been used for several decades to achieve high molecular secondary ion yields in mass spectrometry, there has been no systematic investigation into the ex...