Multiple ionization in strong laser fields

With the ultrashort laser pulses available today, intensities which exceed the binding electrical field of an atom by several orders of magnitude are routinely achieved. As a consequence, it is possible to remove (ionize) one electron or several electrons from an atom within one pulse. The intensity dependence of laser-induced ionization is highly nonlinear and is mostly studied with chemically inert noble gases, using pulses with frequencies in the visible or near-infrared range. For intensities above 10^14 W/cm^2 and femtosecond pulse durations, single ionization (A->A+) can be described very well as a tunneling process with subsequent classical motion of the electron in the laser field. Ionization of \textit{two} electrons can be expressed in terms of two independent single ionization steps (sequential double ionization, A->A+->A2+) if the intensity is high enough (e.g. I>10^15 W/cm^2 for neon). However, for smaller intensities, the measured A2+ ion yields are several orders of magnitude larger than those expected from the sequential mechanism and the transition to the sequential regime leads to a characteristic knee structure in the intensity dependence of the yield. The ionization pathway responsible for the increased production of A2+ ions, i.e. the simultaneous ejection of two electrons (A->A2+), is called nonsequential double ionization (NSDI). For the description of this process, a semiclassical rescattering mechanism has proved successful. According to the rescattering mechanism, an electron tunnels from the atomic potential, is accelerated by the laser field and driven back to the ion where, in an inelastic collision, a second electron is released. With respect to the final momenta of the ionized electrons, the rescattering mechanism also allows for quantitative predictions which are in good agreement with experimental results. The mechanisms of double ionization can be generalized to ionization of an arbitrary number of electrons, with all pathways deviating from the sequential one being referred to as nonsequential multiple ionization. An understanding of triple ionization is of special interest since it is the first case for which several competing nonsequential pathways exist, i.e. simultaneous ionization of three electrons described by the rescattering mechanism (I: A->A3+) and the two combinations of single ionization with NSDI by rescattering (II: A->A+->A3+ and III: A->A2+->A3+). Considering the nonlinear dependence of the tunneling probability on the ionization energies of the participating charge states, one expects that only the pathways I and II contribute significantly to the A3+ yield in the nonsequential intensity regime (e.g. IA+->A2+->A3+), respectively. Based on the predictions of the rescattering mechanism, these transitions should also manifest themselves in the momentum distributions of the A3+ ions. Since experiments could only partially confirm the above expectations, a detailed theoretical investigation of triple ionization is desirable. In this work, quantum mechanical simulations of triple ionization with laser pulses of visible and near-infrared frequencies are presented. To allow for efficient numerical calculations, the motion of the electrons is restricted to a three-dimensional subspace of the full configuration space. This modeling approach has already proved successful in the qualitative investigation of double ionization. From the quantum mechanical wave function of the model, several quantities are calculated which can also be measured experimentally (ion yields, electron and ion momentum distributions) and their dependence on the laser parameters (intensity, frequency, pulse duration) is studied. The main goal of this work is to understand the pathways and mechanisms of triple ionization in the different intensity regimes. For this purpose, we first study the ion yields as a function of intensity. Using one- and two-electron approximations, the yields of the pathways II - IV can be written as products of the yields of the intermediate charge states. This way, it is possible to quantitatively understand the A3+ yields in a wide range of intensities. To quantify the remaining pathway I, rescattering of an electron is analyzed classically (by performing trajectory studies) and quantum mechanically (by considering the time-dependent probability flux). Finally, the insights gained from the product yields and the rescattering analysis are used to interpret the A3+ ion momentum distributions which reflect the change of the prevalent ionization pathway more clearly than the yields. A major result of this work is the importance of classical thresholds for simultaneous multiple ionization. For example, the onset of the regime where the intensity-dependent A3+/A+ yield ratio is approximately constant can be identified with the threshold intensity of simultaneous triple ionization where the energy of the rescattered electron is equal to the sum of the two ionization energies of the A+ ion. Furthermore, the investigation of the A3+ yields indicates that the pathway III plays a much more important role for triple ionization in the nonsequential intensity regime than previously thought. Finally, one has to emphasize the ability of the model to qualitatively reproduce the essential experimental observations on triple ionization

Double ionization of a three-electron atom: Spin correlation effects

We study the effects of spin degrees of freedom and wave function symmetries on double ionization in three-electron systems. Each electron is assigned one spatial degree of freedom. The resulting three-dimensional Schr\"odinger equation is integrated numerically using grid-based Fourier transforms. We reveal three-electron effects on the double ionization yield by comparing signals for different ionization channels. We explain our findings by the existence of fundamental differences between three-electronic and truly two-electronic spin-resolved ionization schemes. We find, for instance, that double ionization from a three-electron system is dominated by electrons that have the opposite spin

Pyrene-DNA Conjugates: Influence of sticky Ends on the Supramolecular Self-Assembly

The supramolecular assembly of DNA conjugates has caught attention in supramolecular chemistry. DNA bears some unique features enabling the design of complex nanostructures. The DNA framework offers a defined spatial arrangement of modifications. In preceding work DNA was modified with phenanthrene at the 3’-ends of DNA forming vesicular supramolecular assemblies with unique light-harvesting properties.[1] Interestingly, the modification of DNA with E-tetraphenylethylenes sticky ends led to aggregation-induced emission (AIE) active assemblies.[2] In this work, we modified a DNA strand at the 3’- and 5’-end with 1,6-pyrene (Figure 1A). We varied the length of the sticky ends to compare their self-assembly properties (1, 2, and 3 pyrene units on either side). For example, AFM measurements of the 1,6-pyrene-DNA conjugates with a total of 6 pyrene units revealed their self-assembly into vesicles (Figure 1B). In addition to AFM studies, fluorescence and UV-vis spectroscopy measurements will be presented and discussed

Restricted space ab initio models for double ionization by strong laser pulses

Double electron ionisation process occurs when an intense laser pulse interacts with atoms or molecules. Exact {\it ab initio} numerical simulation of such a situation is extremely computer resources demanding, thus often one is forced to apply reduced dimensionality models to get insight into the physics of the process. The performance of several algorithms for simulating double electron ionization by strong femtosecond laser pulses are studied. The obtained ionization yields and the momentum distributions of the released electrons are compared, and the effects of the model dimensionality on the ionization dynamics discussed

Supramolecular assembly of pyrene-DNA conjugates: influence of pyrene substitution pattern and implications for artificial LHCs.

The supramolecular self-assembly of pyrene-DNA conjugates into nanostructures is presented. DNA functionalized with different types of pyrene isomers at the 3'-end self-assemble into nano-objects. The shape of the nanostructures is influenced by the type of pyrene isomer appended to the DNA. Multilamellar vesicles are observed with the 1,6- and 1,8-isomers, whereas conjugates of the 2,7-isomer exclusively assemble into spherical nanoparticles. Self-assembled nano-spheres obtained with the 2,7-dialkynyl pyrene isomer were used for the construction of an artificial light-harvesting complex (LHC) in combination with Cy3 as the energy acceptor

FactoryBricks: a New Learning Platform for Smart Manufacturing Systems

Manufacturing industries are facing radical changes under the technological acceleration of Industry 4.0. The manufacturing workforce is not ready for such disruptions due to the lack of vertical skills on digital technologies. Production planning and control of manufacturing systems is often an experience-based art. Further, the companies need of offering training paths for long-life learning of their employees finds several obstacles in the availability of skilled trainers and the trainee’s low engagement with traditional learning models. This paper presents how the FactoryBricks project aims at overcoming the aforementioned issues. The project delivers effective training courses to enable the uptake of industrial technologies and smart manufacturing systems for professionals, either executives or technicians. Beside digital learning contents, the learners are offered an interaction with lab-scale models of production systems built with modular components such as LEGO®. The courses are designed in a modular way, and aim to teach manufacturing concepts in three main topics: (1) the physical system and its dynamics, (2) the physical-digital data connections for smart online analytics, and (3) the exploitation of digital models for production. The paper also presents the results of the prototypical implementation of the project

Graft-versus-Host disease Prophylaxis with Everolimus and Tacrolimus Is Associated with a High Incidence of Sinusoidal Obstruction Syndrome and Microangiopathy: Results of the EVTAC Trial

AbstractA calcineurin inhibitor combined with methotrexate is the standard prophylaxis for graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). Everolimus, a derivative of sirolimus, seems to mediate antileukemia effects. We report on a combination of everolimus and tacrolimus in 24 patients (median age, 62 years) with either myelodysplastic syndrome (MDS; n = 17) or acute myeloid leukemia (AML; n = 7) undergoing intensive conditioning followed by HSCT from related (n = 4) or unrelated (n = 20) donors. All patients engrafted, and only 1 patient experienced grade IV mucositis. Nine patients (37%) developed acute grade II-IV GVHD, and 11 of 17 evaluable patients (64%) developed chronic extensive GVHD. Transplantation-associated microangiopathy (TMA) occurred in 7 patients (29%), with 2 cases of acute renal failure. The study was terminated prematurely because an additional 6 patients (25%) developed sinusoidal obstruction syndrome (SOS), which was fatal in 2 cases. With a median follow-up of 26 months, the 2-year overall survival rate was 47%. Although this new combination appears to be effective as a prophylactic regimen for acute GVHD, the incidence of TMA and SOS is considerably higher than seen with other regimens

Data for the co-expression and purification of human recombinant CaMKK2 in complex with calmodulin in Escherichia coli

AbstractCalcium/calmodulin-dependent kinase kinase 2 (CaMKK2) has been implicated in a range of conditions and pathologies from prostate to hepatic cancer. Here, we describe the expression in Escherichia coli and the purification protocol for the following constructs: full-length CaMKK2 in complex with CaM, CaMKK2 ‘apo’, CaMKK2 (165-501) in complex with CaM, and the CaMKK2 F267G mutant. The protocols described have been optimized for maximum yield and purity with minimal purification steps required and the proteins subsequently used to develop a fluorescence-based assay for drug binding to the kinase, “Using the fluorescent properties of STO-609 as a tool to assist structure-function analyses of recombinant CaMKK2” [1]