Parametrically polarization shaped pulses guided via a hollow core photonic crystal fiber for coherent control

We present ultrafast polarization pulse shaping through a micro structured hollow core photonic crystal fiber. The pulses are shaped in pulse sequences in which the energy, distance, phases, and chirps as well as the state of polarization of each individual sub-pulse can be independently controlled. The application of these pulses for coherent control is demonstrated for feedback loop optimization of the multi-photon ionization of potassium dimers. In a second experiment, this process is investigated by shaper-assisted pump–probe spectroscopy which is likewise performed with pulses that are transmitted through the fiber. Both techniques reveal the excitation pathway including the dynamics in the participating electronic states and expose the relevance of the polarization. These methods will be valuable for endoscopic applications

Simultaneous phase, amplitude, and polarization control of femtosecond laser pulses

We present a serial pulse shaper design which allows us to shape the phase, amplitude, and polarization of fs laser pulses independently and simultaneously. The capabilities of this setup are demonstrated by implementing a method for generating parametrically tailored laser pulses. This method is applied on the ionization of NaK molecules by feedback loop optimization, employing a temporal sub pulse encoding. Moreover, we introduce and characterize a further development of this common path pulse shaper scheme for full control of all light field parameters

Photoassociation and coherent transient dynamics in the interaction of ultracold rubidium atoms with shaped femtosecond pulses - I. Experiment

We experimentally investigate various processes present in the photoassociative interaction of an ultracold atomic sample with shaped femtosecond laser pulses. We demonstrate the photoassociation of pairs of rubidium atoms into electronically excited, bound molecular states using spectrally cut femtosecond laser pulses tuned below the rubidium D1 or D2 asymptote. Time-resolved pump-probe spectra reveal coherent oscillations of the molecular formation rate, which are due to coherent transient dynamics in the electronic excitation. The oscillation frequency corresponds to the detun-ing of the spectral cut position to the asymptotic transition frequency of the rubidium D1 or D2 lines, respectively. Measurements of the molecular photoassociation signal as a function of the pulse energy reveal a non-linear dependence and indicate a non-perturbative excitation process. Chirping the association laser pulse allowed us to change the phase of the coherent transients. Furthermore, a signature for molecules in the electronic ground state is found, which is attributed to molecule formation by femtosecond photoassociation followed by spontaneous decay. In a subsequent article [A. Merli et al., submitted] quantum mechanical calculations are presented, which compare well with the experimental data and reveal further details about the observed coherent transient dynamics

Coherent control with shaped femtosecond laser pulses applied to ultracold molecules

We report on coherent control of excitation processes of translationally ultracold rubidium dimers in a magneto-optical trap by using shaped femtosecond laser pulses. Evolution strategies are applied in a feedback loop in order to optimize the photoexcitation of the Rb2 molecules, which subsequently undergo ionization or fragmentation. A superior performance of the resulting pulses compared to unshaped pulses of the same pulse energy is obtained by distributing the energy among specific spectral components. The demonstration of coherent control to ultracold ensembles opens a path to actively influence fundamental photo-induced processes in molecular quantum gases

Dystonia Linked to EIF4A2 Haploinsufficiency: A Disorder of Protein Translation Dysfunction

Background: Protein synthesis is a tightly controlled process, involving a host of translation-initiation factors and microRNA-associated repressors. Variants in the translational regulator EIF2AK2 were first linked to neurodevelopmental-delay phenotypes, followed by their implication in dystonia. Recently, de novo variants in EIF4A2, encoding eukaryotic translation initiation factor 4A isoform 2 (eIF4A2), have been described in pediatric cases with developmental delay and intellectual disability. Objective: We sought to characterize the role of EIF4A2 variants in dystonic conditions. Methods: We undertook an unbiased search for likely deleterious variants in mutation-constrained genes among 1100 families studied with dystonia. Independent cohorts were screened for EIF4A2 variants. Western blotting and immunocytochemical studies were performed in patient-derived fibroblasts. Results: We report the discovery of a novel heterozygous EIF4A2 frameshift deletion (c.896_897del) in seven patients from two unrelated families. The disease was characterized by adolescence- to adulthood-onset dystonia with tremor. In patient-derived fibroblasts, eIF4A2 production amounted to only 50% of the normal quantity. Reduction of eIF4A2 was associated with abnormally increased levels of IMP1, a target of Ccr4-Not, the complex that interacts with eIF4A2 to mediate microRNA-dependent translational repression. By complementing the analyses with fibroblasts bearing EIF4A2 biallelic mutations, we established a correlation between IMP1 expression alterations and eIF4A2 functional dosage. Moreover, eIF4A2 and Ccr4-Not displayed significantly diminished colocalization in dystonia patient cells. Review of international databases identified EIF4A2 deletion variants (c.470_472del, c.1144_1145del) in another two dystonia-affected pedigrees. Conclusions: Our findings demonstrate that EIF4A2 haploinsufficiency underlies a previously unrecognized dominant dystonia-tremor syndrome. The data imply that translational deregulation is more broadly linked to both early neurodevelopmental phenotypes and later-onset dystonic conditions. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Parametrische Methoden der Polarisationspulsformung und Kontrolle der Anregungsdynamik in ultrakaltem Rubidium

This work focuses on the developments of ultrafast laser pulse shaping techniques and their application to diatomic molecular systems in order to reveal fundamental effects in light matter interaction. It describes the development of a new pulse shaper consisting of a sequence of four liquid crystal arrays and a polarizer. This pulse shaper is the first non- interferometric setup for unrestricted phase, amplitude, and polarization shaping. Moreover, a parametric encoding of the electrical field was developed which allowed for generating pulse sequences consisting of several sub-pulses. Each sub-pulse can be controlled in its physically apparent parameters: energy, position in time, phase, and chirps as well as state of polarization with ellipticity, orientation, and helicity. The feasibility of the setup is illustrated by systematic variations of single and double pulses, which are experimentally generated and measured. In these series of pulses, one of the pulses parameters is varied while the other parameters are kept constant. This proves the precise control of the pulse shape. Further, more complex pulses are shown to give an impression of the capabilities of this setup in combination with the parameterization. For some fields of application, it could be desirable to guide the phase, amplitude and polarization shaped pulses through an optical fiber. For example, life science could benefit from shaped pulses in the area of imaging and photodynamic therapy. In order to make the shaped pulses available at the distal end of an optical fiber, the effects of the fiber have to be compensated. In this work, the generation of phase, amplitude, and polarization shaped pulses after transmission trough an optical fiber is presented. This is demonstrated for two types of optical fibers – a standard single-mode fiber and a microstructured hollow core photonic crystal fiber. The procedure for the determined generation of parametrically shaped pulses differs for both types of optical fibers. The capabilities of parametrically shaped pulse sequences are – again – illustrated by a series of example pulses. The parametrically shaped pulses transmitted through the hollow core fiber are implemented in a coherent control experiment. For this purpose, the potassium dimer produced in a molecular beam serves as a test system. The multi-photon ionization is studied by a closed feedback loop optimization and shaper-assisted pump-probe spectroscopy. These experiments revealed the excitation path including the vibrational dynamics in the first and second excited state. Further, the relevance of the polarization control in the excitation process is highlighted. Moreover, coherent control techniques are applied to investigate the interaction of shaped femtosecond laser pulses with ultracold atoms and molecules. The focus of these experiments is the control of the photoassociation of a colliding atom pair to a bound molecule. This process is investigated using two-color pump-probe spectroscopy. The molecular transients are compared to theoretical calculations. The analysis of this data reveals the interaction process which is discussed in the time and frequency domain. In a second experiment, the multi-photon ionization of ultracold rubidium dimers is optimized in a closed feedback loop. In this optimization, a parameterization in the frequency domain is employed which extracts the relevant transition frequencies. In combination with a complementary experiment the excitation pathway was revealed.Kern dieser Arbeit ist die Manipulation von ultrakurzen Laserpulsen und deren Anwendung auf molekulare Quantensysteme. Zwecks uneingeschränkter Formung der Phase, Amplitude und Polarisation von Laserpulsen wurde ein neuer Pulsformer entwickelt. In diesem nicht-interferometrischen Aufbau werden vier aufeinander folgende Flüssigkristallarrays für die Modulation des Lichtfeldes verwendet. Für die gezielte Kontrolle des geformten elektrischen Feldes wurde ein Verfahren zur Erstellung von Pulssequenzen entwickelt. Die Unterpulse dieser Sequenzen können in ihren physikalisch intuitiven Parametern Energie, zeitliche Position, Phase, Chirps und der Polarisation, die durch die Orientierung, die Elliptizität und die Helizität gegeben ist, individuell kontrolliert werden. Die Funktionsweise des Pulsformers und der Parametrisierung wird anhand von experimentell erstellten und charakterisierten Pulsen veranschaulicht. Pulsformen von höherer Komplexität bieten Einblicke in die Möglichkeiten und die Präzision der vorgestellten Methoden. Für einige Anwendungsgebiete ist es wünschenswert, die geformten Laserpulse durch optische Fasern zu transportieren. Insbesondere würde im Bereich Biowissenschaften und Medizin von endoskopisch verfügbaren Femtosekunden-Laserpulsen profitiert werden. In dieser Arbeit wird die Erstellung von ultrakurzen Laserpulsen vorgestellt, die nach der Transmission durch optische Fasern gezielt in Phase, Amplitude und Polarisation geformt werden. Hierbei müssen die speziellen Eigenschaften der Faser berücksichtigt werden. Dies wird exemplarisch für eine konventionelle Step-Index-Glasfaser sowie für eine photonische Hohlkern-Kristall-Faser gezeigt. Aufgrund der unterschiedlichen Eigenschaften dieser Fasern ist zur Erstellung parametrisch geformter Pulse ein jeweils eigenständiges Verfahren notwendig. Ähnlich wie bei der Vorstellung des Pulsformers werden die Möglichkeiten der Kontrolle der Pulssequenzen mit Beispielpulsen belegt. Die durch die Faser transmittierten und in Phase, Amplitude und Polarisation parametrisch geformten Pulse werden zur Untersuchung der Moleküldynamik genutzt. Zu diesem Zweck wird die Mehrphotonen-Ionisation des Kalium-Dimers in einem Molekularstrahl in einer Rückkopplungsschleife unter Verwendung evolutionärer Algorithmen optimiert. Ferner wird eine durch den Pulsformer erstellte Doppelpulssequenz für zeitaufgelöste Pump-Probe-Messungen genutzt. Beide Experimente geben Aufschluss über die Vibrationsdynamik und den Anregungsweg der Moleküle. Dabei wird die Relevanz der Polarisationsänderung für den Prozess der Mehrphotonen- Ionisation deutlich. In einem weiteren Experiment werden Methoden der kohärenten Kontrolle angewendet, um die Wechselwirkung zwischen geformten ultrakurzen Laserpulsen und ultrakalten Atomen und Molekülen zu untersuchen. Die Kontrolle und Untersuchung der Photoassoziation eines ultrakalten atomaren Sto"spaares zu einem gebundenen Molekül war hier von besonderem Interesse. Dieser Prozess wurde mittels Zweifarben-Pump-Probe-Spektroskopie untersucht. Die experimentell erhaltenen Transienten wurden mit theoretischen Berechnungen verglichen. Deren Analyse gab Aufschluss über die Wechselwirkung, die in der Zeit- und Frequenzdomäne diskutiert wird. Des Weiteren wird die Mehrphotonen- Ionisation des ultrakalten Rubidium-Dimers in einer Rückkopplungsschleife optimiert. Hierfür wurde zur Identifikation der für die Anregung relevanten Frequenzen eine Parametrisierung des Pulses in der Frequenzdomäne genutzt. In Verbindung mit den Ergebnissen eines komplementären Experiments konnte der Anregungsprozess erfolgreich entschlüsselt werden

An experimental and numerical survey into the potential of hybrid foams

Hybrid foams are composite materials consisting of two foamed constitutive materials. Compared to conventional mono material foams, hybrid foams have the advantage that their material properties can be adapted more easily to comply with any kinds of prescribed requirements deriving from the intended structural application. The present study is concerned with a survey of the mechanical properties of a variety of hybrid foams with both, interpenetrating and particulate microstructures. As constituent foams, polymeric, metallic and ceramic foams of different types are considered. In an experimental survey, the mechanical response of the hybrid foams is characterized under compression with loading rates covering the entire spectrum from quasi-static conditions up into the high rate regime. The experimental investigation is complemented by a numerical simulation using a hierarchical homogenization procedure to predict the effective material properties numerically. The experimental and numerical results reveal that the hybrid foam concept provides the opportunity to design lightweight cellular solids with effective mechanical properties in a wide range. The optimization potential is demonstrated in a case study considering the design of a material for a bird-strike protection system for commercial aviation

Berichte vom Historikertag 2016

Unter dem Motto „Glaubensfragen“ fand vom 20. bis 23. September 2016 der 51. Deutsche Historikertag an der Universität Hamburg statt. H-Soz-Kult und Clio-online haben als offizieller Medienpartner das Organisationsbüro mit Ankündigungen im Vorfeld begleitet. Nach dem Historikertag wurde über zahlreiche Sektionen und Podiumsdiskussionen berichtet, in Form der bekannten Sektions- und Querschnittsberichte. In Zusammenarbeit mit den Veranstaltern der Sektionen konnten viele Autorinnen und Autoren gewonnen werden, die in ihren Berichten die Ergebnisse einzelner Sektionen dokumentieren, sie in einen größeren Kontext stellen oder kritisch analysieren. Einige Querschnittsberichte ergänzen die Sektionsberichte nicht nur, sondern nehmen darüber hinaus epochale oder thematische Zugänge mehrerer Sektionen in den Blick und machen so übergreifende Fragestellungen sichtbar