Photoelectron imaging of XUV photoionization of CO2 by 13-40 eV synchrotron radiation

Valence band photoionization of CO2 has been studied by photoelectron spectroscopy using a velocity map imaging spectrometer and synchrotron radiation. The measured data allow retrieving electronic and vibrational branching ratios, vibrationally resolved asymmetry parameters, and the total electron yield which includes multiple strong resonances. Additionally, the spectrum of low kinetic energy electrons has been studied in the resonant region, and the evolution with photon energy of one of the forbidden transitions present in the slow photoelectrons spectrum has been carefully analyzed, indicating that in the presence of auto-ionizing resonances the vibrational populations of the ion are significantly redistributed

Strong field ionization of small hydrocarbon chains with full 3D momentum analysis

Strong field ionization of small hydrocarbon chains is studied in a kinematic complete experiment using a reaction microscope. By coincidence detection of ions and electrons different ionization continua populated during the ionization process are identified. In addition, photoelectron momentum distributions from laser-aligned molecules allow to characterize the electron wavepackets emerging from different Dyson orbitals

Starkfeldionisation von Atomen und Molekülen: Koinzidenzmessungen mit hoher Wiederholrate

The combination of strong few-cycle laser pulses with a reaction microscope, a spectrometer capable of detecting the momentum-vectors of all charged particles that emerge from ionization or dissociation processes in coincidence, enables precise and detailed investigations of strong field processes that occur in atoms and small molecules. However, to avoid false coincidences, experiments with a reaction microscope rely on a low ratio between event rate and laser rate. Common repetition rates of strong few cycle laser systems are on the order of a few kHz leading to long measurement duration up to several days to get reliable information e.g. on angular and energy resolved data. If, in addition, laser parameters such as pump probe delay or polarization have to be scanned, the duration for such experimental runs can extend even beyond this time scale. For such long time periods it is very difficult to maintain stable experimental conditions. Hence, the possibility to scan through large parameter sets is very limited. To overcome this limitation, we combined a reaction microscope with a 400 kHz high repetition rate NOPA-system delivering strong few-cycle laser pulses to study multi-electron dynamics in strong field ionization experiments. First measurements on strong field ionization of argon were performed to characterize the setup. In these experiments unexpected sharp structures have been observed in the electron momentum distributions. With the help of TDSE (Time Dependent Schrödinger Equation) calculations, it was found that these sharp structures originate from the temporal shape of the laser pulses which contains weak post pulses. In this 'unwanted' pump probe scheme, the strong main pulse not only ionizes the argon atom but also populates Rydberg states in the neutral atom. A weaker post pulse ionizes the Rydberg states. This leads to interferences between the direct and the indirect created photo electrons and thus to sharp structures in the electron spectra. The TDSE calculation has shown that the relative population and initial phases of Rydberg states populated by the strong field interaction can be extracted when studying the time dependence of these interferences in a pump probe experiment.Die Kombination starker kurzer Laserimpulse von wenigen Zyklen mit einem Reaktionsmikroskops, welches die Impulsvektoren aller geladenen Teilchen, die aus einem Ionisations- oder Dissoziationsprozess stammen, koinzident detektieren kann, ermöglicht eine genaue und detaillierte Untersuchung von atomaren und molekularen Starkfeldprozessen. Experimente mit Reaktionsmikroskopen bedürfen jedoch eines niedrigen Verhältnisses zwischen Ereignisrate und Laserrate, um falsche Koinzidenzen zu vermeiden. Gewöhnliche Wiederholraten von Lasersystemen, die starke Laserimpulse mit wenigen Zyklen erzeugen, sind in der Größenordnung weniger kHz. Dies führt zur Messdauern von bis zu einigen Tagen für verlässliche Informationen über z.B. winkel- und energieaufgelöste Daten. Falls zusätzlich noch Laserparameter wie Polarisation oder der zeitliche Abstande zweier Laserimpulse variiert werden soll, kann die Dauer eines solchen Experimentes sogar noch größere Zeitskalen erreichen. Es ist sehr schwierig Experimente auf diesen Zeitskalen stabil zu halten. Deshalb sind die Möglichkeiten große Parameterräume zu durchsuchen stark eingeschränkt. Wir haben ein Reaktionsmikroskop mit einem NOPA-System kombiniert, das starke, kurze Laserimpulse von wenigen Zyklen mit einer Wiederholrate von 400 kHz erzeugt, um diese Einschränkung zu überwinden und Mehrelektronendynamiken in Starkfeldexperimenten zu untersuchen. Es wurden erste Experimente mit Starkfeldionisation an Argon durchgeführt, um den experimentellen Aufbau zu charakterisieren. Die Impulsverteilungen der Elektronen aus diesen Experimenten zeigten unerwartet scharfe Strukturen. TDSE (Time Dependent Schrödinger Equation) Berechnungen zeigten, dass diese Strukturen durch die zeitliche Form des Laserimpulses, der schwache Satellitenimpulse enthält, verursacht wurden. In diesem ungewollten pump-probe Schema ionisiert der starke Hauptimpuls nicht nur das Argonatom, sondern er bevölkert auch gleichzeitig Rydbergzustände des neutralen Atoms. Die Rydbergzustände werden durch einen späteren schwächeren Impuls ionisiert. Dies führt zu Interferenzen zwischen den direkt und indirekt erzeugten Photoelektronen sichtbar als scharfe Strukturen in den Elektronenspektren. Zusätzlich zeigte die TDSE-Berechnung, dass die relative Population und die initialen Phasen der Rydbergzustände, die durch die Starkfeldinteraktion bevölkert werden, aus den Photoelektronenspektren extrahiert werden können, wenn die Zeitabhängigkeit dieser Interferenzen durch ein Pump-Probe-Experiment untersucht wird. In einem anderen Starkfeldexperiment an mehratomigen Molekülen wie Butadien und n-Butan untersuchten wir deren Fragmentation. Es wurden winkelaufgelösten Photoelektronenspektren für unterschiedliche Fragmentationskanäle aufgenommen. Diese Messungen zeigten, dass unterschiedliche ionische Zustände während einer Starkfeldionisation bevölkert werden. Dies deutet daraufhin, dass in mehratomigen Molekülen nicht nur das am schwächsten gebundene Elektron in Starkfeldionisationsprozessen teilnimmt

Mortality of Adult Respiratory Distress Syndrome in Trauma Patients: A Systematic Review over a Period of Four Decades

BACKGROUND Acute respiratory distress syndrome (ARDS) is associated with high morbidity and mortality. In addition, its aetiologies are heterogeneous, and the outcome depends on the underlying cause. In trauma care, changes in diagnostics, management and treatment may influence the outcome of posttraumatic ARDS over time, which are attributable to geographic distribution, relate to the definition used and depend on the injury severity. METHODS We selected studies by searching PubMed using the MeSH terms "acute respiratory distress syndrome", "mortality" and "trauma" and all their combinations. Studies that reported mortality rates for polytrauma patients with ARDS were included. We excluded studies with selected population collectives (e.g. burn patients, isolated thoracic trauma and paediatric trauma) and non-trauma studies. Studies were stratified according to the recruitment year of patients into Decade 1 (prior 1990), Decade 2(1990-1999), Decade 3 (2000-2009) and Decade 4 (later 2009); geographic location (North America or Europe), the definition used in the different studies (American European Consensus Conference (AECC) definition or Berlin definition) and the mean injury severity of the patient populations, respectively. RESULTS Twenty-three studies between 1 January 1980 and 30 June 2018 were included in the analysis (486,861 patients, 52,561 with posttraumatic ARDS). There was a wide variation in mortality rates among the studies (4-39%). The overall pooled mean mortality rate for all studies was 21.8%, SD ± 8.3%. The mean mortality over the last four decades was similar between decade 1 (25.8%), decade 2 (20.6%), decade 3 (20.7%) and decade 4 (22.5%). Geographical observations comparing Europe and North America revealed no difference [Europe (22.1%) and North America (21.7%)]. The ARDS mortality in publications using the Berlin definition (23%) was comparable to the mortality rate in publications using the AECC definition (22.9%). The mortality rate based on the injury severity showed no alteration (ISS ≤ 25 points, 22.6%, ISS > 25 points, 22.6%). CONCLUSION In this systematic review, there was no change in the mortality rate over the last four decades, no geographical difference within Western societies, no dependence on the ARDS definition used and no association with injury severity, respectively