Coulomb Explosion and Intense-Field Photodissociation of Ion-Beam H2+ and D2+

As the simplest molecule in nature, the hydrogen molecular ion provides a unique system for studying molecules in intense laser fields. In this thesis, the Coulomb explosion and photodissociation channel of H2+ and D2+ have been investigated with 790-nm, sub-100-fs laser pulses by employing a high-resolution photofragment imaging technique. Unlike most experiments, where neutral molecules were used as a target, in this work molecular ions were prepared by an electric discharge, providing well-defined starting conditions and allowing experiments at lower intensities. At intensities close to the threshold for Coulomb explosion (<10^14 W/cm^2), we observed a peak structure in the Coulomb explosion kinetic energy spectra in both H2+ and D2+. We show that the observed peaks can be attributed to the different dissociation energies of vibrationally excited molecules. Furthermore, this preservation of the vibrational structure during the Coulomb explosion suggests ionization at one well-defined critical internuclear distance. Moreover, when using pulses with durations of 200-500 fs, we found three Coulomb explosion kinetic energy groups with different angular distributions in both molecular ions. The groups in D2+ at a pulse duration of 350 fs and an intensity of 1x10^14 W/cm^2 strongly suggest critical internuclear distances of 8, 11 and 15 a.u. In the one-photon photodissociation study of D2+ at intensities below 2x10^14 W/cm^2, we obtained vibrationally resolved fragment velocity distributions. With increasing intensity, we observed the effects of bond softening - narrowing of the angular distributions and vibrational level shifting. These effects were also found in H2+ and are in agreement with the model of light-induced potentials. In addition, in the kinetic energy spectra of D2+, we found the smaller widths of the vibrational peaks, which we interpret as being due to the longer lifetimes of the vibrational states of D2+ against photodissociation. Moreover, we observed fragments with near-zero kinetic energies with broad angular distributions, indicating dissociation through a vibrational trapping mechanism. In the two-photon bond softening process (above-threshold dissociation) of H2+, we identified fragments from the single vibrational level v=3. At higher intensities, lower-energy fragments with increasing alignment were observed, suggesting dissociation of the levels v<3 through the barrier lowering mechanism. These results provide a basis for quantum mechanical simulations that could lead to a better understanding of the molecular dynamics in intense fields.Das elementarste Molekül in der Natur, das Wasserstoff-Molekülion, stellt ein einzigartiges System für die Untersuchung von Molekülen in intensiven Laserfeldern dar. In dieser Dissertation wurden die Coulomb-Explosion und die Photodissoziation des H2+ und D2+ mit 790-nm, sub-100-fs Laserpulsen unter Verwendung einer hochauflösenden Photofragment Abbildungstechnik untersucht. Im Gegensatz zu den meisten Experimenten, in denen neutrale Moleküle als Ausgangsmoleküle benutzt wurden, wurden in dieser Arbeit die Molekülionen durch eine elektrische Gasentladung erzeugt, was zu wohldefinierten Ausgangsbedingungen führte und Experimente mit relativ niedrigen Laserintensitäten ermöglichte. Bei Intensitäten nahe der Schwelle der Coulomb-Explosion (<10^14 W/cm^2), beobachten wir eine Peak-Struktur in den kinetischen Energiespektren der Fragmente der Coulomb-Explosion sowohl bei H2+ als auch bei D2+. Wir stellen fest, dass die beobachteten Peaks den unterschiedlichen Dissoziationsenergien der vibrationsangeregten Moleküle zugeordnet werden können. Die Erhaltung der Vibrationsstruktur bei der Coulomb-Explosion deutet darauf hin, dass die Ionisation bei einem scharfen kritischen internuklearen Abstand stattfindet. Als wir Laserpulse mit einer Dauer von 200–500 fs verwendeten, entdeckten wir drei Coulomb-Explosions Zentren in den kinetischen Energiespektren mit unterschiedlichen Winkelverteilungen bei beiden molekularen Isotopomeren. So entsprechen die Gruppen bei D2+ bei einer Pulsdauer von 350 fs und einer Intensität von 1x10^14 W/cm^2 kritischen internuklearen Abständen von 8, 11 und 15 a.u. Bei der Untersuchung der 1-Photonen Photodissoziation des D2+ beobachten wir bei einer Intensität unterhalb 2x10^14 W/cm^2 vibrationsaufgelöste Geschwindigkeitsverteilungen der Fragmente. Mit zunehmender Intensität beobachten wir auch Effekte des bond softenings – Einengung der Winkelverteilung und Verschiebung der Vibrationsniveaus. Diese Effekte wurden auch schon vorher bei H2+ beobachtet und finden ihre Erklärung in dem Modell der lichtinduzierten Potenziale. Insbesondere finden wir in den kinetischen Energiespektren von D2+ kleinere Breiten der Vibrationspeaks, deren Ursache längere Lebensdauern der Vibrationszustände von D2+ bei der Photodissoziation sein sollten. In dem Prozess des 2-Photonen bond softenings von H2+ identifizieren wir Fragmente des einzelnen Vibrationsniveaus v=3. Bei höheren Intensitäten wurden niederenergetische Fragmente mit zunehmender Ausrichtung in Polarisationsrichtung beobachtet, die auf Dissozation durch eine Barriereabsenkung hinweisen. Diese experimentellen Ergebnisse können durch quantenmechanische Rechnungen simuliert werden, die zu einem besseren Verständnis der Molekulardynamik in intensiven Laserfeldern führen werden

The light distribution in OLEDs and ways to increase the light outcoupling efficiency

Power efficiency of organic light emitting devices (OLEDs) is in the focus of worldwide research in order to reduce power consumption of displays and to improve the competitive situation of OLEDs for lighting devices. The optical properties of OLEDs are studied with the aim to enhance the fraction of light coupled out of these devices. Simulation software has been used to analyze the transfer of internally generated emission into usable external light modes. Results from modeling have been compared to experimental data to build trust into the validity of the results. Critical parameters influencing outcoupling properties have been identified. Thus, 185lm/W at 1000cd/m2 have been achieved for a green PIN-OLED using a high-n substrate & half ball lens. Finally, some conclusions for the design of outcoupling enhancing means are drawn

An overview about the use of electrical doping of charge carrier transport layers in OLEDs and further organic electronic applications

Electrical doping of organic layers is now a well established method for building highly efficient and long living OLEDs. A unique class of OLED devices called PIN-OLEDs based on redox doping technology is emerging as one key technology for OLED applications. These devices exhibit high power efficiency and long life time, which are critical parameters for commercial success. Moreover, PIN OLEDs offer high degree of freedom in choosing layer structures for optimizing the device performance for specific lighting and display applications. For example, optimizing color and power efficiency of OLEDs can be easily achieved without compromising the device operating voltage. It is worth to mention that PIN OLEDS, especially the red emitting PIN OLEDs, exhibit record breaking half life time of more than one million hours with the starting device brightness of 1000 cd/m(2). The doping technology also offers benefits to other organic electronic devices such as OTFTs and photovoltaic devices. This paper briefly discusses the improvements made on the OLED device performance such as power efficiency and lifetime using doped transport layers. Few examples of device optimization using doped layers are presented in detail. In addition, a brief discussion on performance of doped transport layers in photovoltaics is also presented

Satisfaction with psychiatric in-patient care as rated by patients at discharge from hospitals in 11 countries

Purpose: There is disregard in the scientific literature for the evaluation of psychiatric in-patient care as rated directly by patients. In this context, we aimed to explore satisfaction of people treated in mental health in-patient facilities. The project was a part of the Young Psychiatrist Program by the Association for the Improvement of Mental Health Programmes. Methods: This is an international multicentre cross-sectional study conducted in 25 hospitals across 11 countries. The research team at each study site approached a consecutive target sample of 30 discharged patients to measure their satisfaction using the five-item study-specific questionnaire. Individual and institution level correlates of ‘low satisfaction’ were examined by comparisons of binary and multivariate associations in multilevel regression models. Results: A final study sample consisted of 673 participants. Total satisfaction scores were highly skewed towards the upper end of the scale, with a median total score of 44 (interquartile range 38–48) out of 50. After taking clustering into account, the only independent correlates of low satisfaction were schizophrenia diagnosis and low psychiatrist to patient ratio. Conclusion: Further studies on patients’ satisfaction should additionally pay attention to treatment expectations formed by the previous experience of treatment, service-related knowledge, stigma and patients’ disempowerment, and power imbalance.</p