Since the surprising first detection of small carbon cluster dianions by Compton et al 1990, several studies have been made investigating their structure, fragmentation pathways and stability. As other carbon anions have been found in space, it is likely that these dianions exists as well and their ability to react with other molecules is therefore of interest. Previous studies have shown that they may survive on microsecond timescales, but it is still an open question whether they are metastable or thermodynamically stable. Therefore, this study utilizes the cyrogenic storage ring DESIREE to investigate the lifetime and stability of carbon cluster dianions Cn(2-) (n=7-10) in the new domains. Dianions were produced with a cesium ion sputtering source and their spontaneous decay Cn(2-) -> Cn(-) + e- was monitored for almost 100 ms by detection of the singly charged decay products. Also, the extra electron's tunneling probability through the repulsive coloumb barrier for C8(2-) was calculated and the lifetime for different energy states was estimated. Analyzing the DESIREE data, the lifetime of the dianions could be determined to exceed the previous concluded lifetimes of 10 us by a whole order of magnitude. The only way to detect stable ions after that would be if they collided with rest gas and due to good vacuum, this eventual signal is too low. Probably due to varying structures, an alternating pattern was found, dianions with even n decaying slower than their odd neighbours. The fitting of power laws to the data is consistent with that the dianions were produced with a broad internal energy distribution. Calculations for C8(2-) indicated that its electron affinity had to be at least -1eV in order to agree with the experimental results. Continuing the investigations, future studies could, after sufficient time, use DESIREE in an alternative way, allowing detection of possible stable dianions.

No description available.

Cavity enhanced optical frequency comb spectroscopy is a technique that allows for quick and sensitive measurements of molecular absorption spectra. Locking the comb lines of an optical frequency comb to the cavity modes of an enhancement cavity and then extracting the spectral information with a Fourier transform spectrometer grants easy access to wide segments of absorption spectra. One of the main obstacles complicating the analysis of the measurements is the inevitable dispersion occurring inside the cavity. In this project, absorption measurements of CO2 were performed using an existing and well established setup consisting of a near-infrared optical frequency comb locked to a Fabry- Pérot enhancement cavity using the Pound-Drever-Hall technique, and a Fourier transform spectrometer. The purpose was to improve theoretical models of the measured absorption spectra by creating and verifying a model for the cavity dispersion, stemming mostly from the cavity mirrors but also from the normal dispersion of the intracavity medium. Until now, the cavity dispersion has been treated as an unknown and was included as a fitting parameter together with the CO2 concentration when applying fits to the absorption measurements. The dispersion model was based on previously performed precise measurements of the positions of the cavity modes. The model was found to agree well with measurements. In addition, pre-calculating the dispersion drastically reduced computation time and seemed to improve the overall robustness of the fitting routine. A complicating factor was found to be small discrepancies between the locking frequencies as determined prior to the measurements and the values yielding optimum agreement with the model. These apparent shifts of the locking points were found to have a systematic dependence on the distance between the locking points. The exact cause of this was not determined but the results indicate that with the locking points separated by more than about 10nm the shifts are negligible.

Multilayered interference coatings based on titanium- and zirconium nitride and designed for solar control have been prepared using reactive d c magnetron sputtering. Preparation effects and degradation mechanisms were investigated. It was shown that the quality of the nitride strongly depends on the degree of crystallinity in the underlying oxide. It has been shown that the nitride layer partly oxidizes as the top oxide layer is deposited. The degradation is enhanced with temperature. A thin sacrificial layer of aluminium deposited between successive depositions of nitride and oxide is shown to improve the optical performance of the coating as preparedm as well as after accelerated ageing tests. The optical properties of opaque and semitransparent films of zirconium nitride have been studied. A thorough investigation of the influence of composition, deposition rate, substrate temperature and film thickness on the optical response of the film was performed. Both photometric and ellipsometric methods were used to determine thicknesses and the optical constants at wavelengths ranging from 0.23 to 25 μm. The resulting values of n and k, in the wavelength intervals where these independent methods are applicable, have been shown to agree extremely well. The results so far indicate an even larger potential for zirconium nitride based solar control coatings as compared to the titanium nitride based. Access to optical constants derived from films of zirconium nitride of variable quality made multilayer modelling a powerful tool in the design and analysis of solar control coatings.

This thesis outlines the fabrication of two atom chips for the study of interactions between ⁸⁷Rb Rydberg atoms and a Au surface. Atom chips yield tightly confined, cold samples of an atomic species by generating magnetic fields with high gradients using microfabricated current-carrying wires. These ground state atoms may in turn be excited to Rydberg states. The trapping wires of Chip 1 are fabricated using thermally evaporated Cr/Au and patterned using lift-off photolithography. Chip 2 uses a Ti/Pd/Au tri-layer, instead of Cr/Au, to minimize interdiffusion. The chip has a thermally evaporated Au surface layer for Rydberg atom-surface interactions, which is separated from the underlying trapping wires by a planarizing polyimide dielectric. The polyimide was patterned using reactive ion etching. Special attention was paid to the edge roughness and electrical properties of the trapping wires, the planarization of the polyimide, and the grain structure of the Au surface.

This thesis outlines the fabrication of two atom chips for the study of interactions between ⁸⁷Rb Rydberg atoms and a Au surface. Atom chips yield tightly confined, cold samples of an atomic species by generating magnetic fields with high gradients using microfabricated current-carrying wires. These ground state atoms may in turn be excited to Rydberg states. The trapping wires of Chip 1 are fabricated using thermally evaporated Cr/Au and patterned using lift-off photolithography. Chip 2 uses a Ti/Pd/Au tri-layer, instead of Cr/Au, to minimize interdiffusion. The chip has a thermally evaporated Au surface layer for Rydberg atom-surface interactions, which is separated from the underlying trapping wires by a planarizing polyimide dielectric. The polyimide was patterned using reactive ion etching. Special attention was paid to the edge roughness and electrical properties of the trapping wires, the planarization of the polyimide, and the grain structure of the Au surface.

Στο παρόν κείμενο μελετώνται οι τεχνικές υλοποίησης L2 MPLS VPNs Cicruit Cross Connect (CCC) και Any Trasfer over MPLS (AToM) που παρέχουν οι δύο κύριοι κατασκευαστές δικτυακού υλικού Juniper και Cisco αντίστοιχα. Πρόθεση της μελέτης είναι να διερευνηθούν τα ιδιαίτερα τεχνικά χαρακτηριστικά της κάθε τεχνικής και στην συνέχεια να μελετηθούν τρόποι επίτευξης της διαλειτουργικότητας μεταξύ των δύο. Το τελευταίο είναι χρήσιμο στην περίπτωση που μια υπηρεσία παροχής L2 MPLS VPNs επεκτείνεται σε ένα δίκτυο που αποτελείται από εξοπλισμό και των δύο κατασκευαστών. Στην ιδιαίτερη περίπτωση του ΕΔΕΤ το οποίο είναι ένα αμιγώς «Cisco» δίκτυο το παραπάνω έχει εφαρμογή στο όριο διασύνδεσης με το GEANT το οποίο αντίστοιχα είναι ένα αμιγώς «Juniper» δίκτυο. Συνεπώς η παροχή L2 MPLS VPN μεταξύ οποιουδήποτε φορέα που συνδέεται στο ΕΔΕΤ( πχ ενός ακαδημαϊκού ιδρύματος) και ενός άλλου φορέα που είναι πίσω από το Geant ( φυσικά εκτός ΕΔΕΤ) προϋποθέτει την επίλυση των προβλημάτων διαλειτουργικότητας μεταξύ των δύο τεχνικών. / The subject of this paper is the implementation techniques of L2 MPLS VPNs Cicruit Cross Connect (CCC) and Any Trasfer over MPLS (AtoM) that are provided by the two main manufactures of network connection (Juniper and Cisco). Furthermore this paper searches the special technical features of each technique and tries to find ways of interoperability between those two. This is useful when a providing L2 MPLS VPNs service expands in a network that consists of equipment of these two main manufactures . In the special occasion of EDET, which is a completely «Cisco» network the upper has implementation in the connection limits with GEANT, which is a completely «Juniper» network. Therefore the providing of L2 MPLS VPN between any carrier that is connected with EDET (eg. Academic Institute) and another carrier that is behind GEANT (of course out of EDET) presupposes the solution of the interoperability problems between these techniques.

Universiẗat, Diss., 2003--Kaiserslautern.

Only very few molar polarizabilities are known with high accuracy; and when so, they are in general only known at a given wavelength. There is therefore a need to assess the molar polarizability with high accuracy of various gases, at different wavelengths. The molar polarizability of a gas is a measure of the susceptibility of a molecule to have its charge distribution affected by light. It is also the entity that relates the index of refraction to the (molar) density of a gas in Lorentz-Lorenz equation. Hence, for high precision measurements of the density of a gas, it is important to know the molar polarizability of the gas to high accuracy. In this work a GAMOR system has been used to determine the wavelength-dependent molar polarizability of Ar at 1550 nm.  However, a high accuracy assessment of the molar polarizability of a gas requires that the gas density is known with high accuracy. Since this is not trivial to assess, the molar polarizability of argon has been assessed in terms of that of nitrogen, which is assumed to be known with high accuracy. Hence, to minimise measurement errors, the measurement cavity was alternately filled with nitrogen and argon and the ratio between the signals provided by the GAMOR system represents the ratio of the molar polarizabilities of the two gases. It was found that the molar polarizability of argon was  0.94393(5) times that of nitrogen. Since the latter one has been assessed to 4.34828(3) x 10^-6  m^/mol, the molar polarizability of argon could be assessed to 4.10446(5) x 10^-6 m^3/mol.

In the last decades the scientific development has made it possible to produce pulses with durations below the femtosecond time scale (1 fs = 1015 s), reaching to attoseconds (1 as = 1018 s). This is the time scale of electronic motion inside atoms and molecules. One way to produce isolated attosecond pulses is through high harmonic generation in gases with intense few-cycle laser pulses. This process depends strongly on the electric field shape relative to the pulse envelope, which is characterized by the so called carrier-envelope phase (CEP).The goal of this master’s thesis is to measure and investigate the possibility to improve the CEP stability of sub-two-cycle laser pulses from the laser, Light Wave Synthesizer 20 (LWS-20). The first step of the master’s thesis was to modify a Labview program used to evaluate the CEP change to be able to reevaluate the already acquired raw data. The measurements are done with an f-to-2f interferometer, whichis a spectral interference device, which measures the CEP difference between two pulses. The CEP change of the laser system was measured at three positions: after the multi-pass amplifier of the laser front end (MP), after a hollow-core fiber (HCF), which is used for spectral broadening, and at the end of the laser system. The stability is determined as the RMS error (standard deviation) of the phase change overall shots in one sample (lower RMS is better stability). The measurements show an average stability of 160±20 mrad RMS after the MP, 280±31 mrad RMS after the HCF and 560±53 mrad RMS at the end of the system. The stability at the end of the system could be improved to 475±40 mrad RMS after a scan of the pump energy for one of the amplifier stages. The HCF appears to provide a lower limit in stability and influences it only if it is very good after the MP. The alignment of the HCF does also seem to influence the CEP stability and the best stability appears to coincide with maximum output energy. An acousto-optic modulator (Dazzler) has been used to manipulate the CEP change at the end of the system and can thereby compensate for long-term drifts, but the source of the CEP stability degradation at the end of the system should be further investigated.