Essays on fiscal sustainability in Europe

Fiscal sustainability is present when the current government debt equates to the present value of future budget surpluses or their excess over deficits but since 1970 the EU countries on average had a surplus budget only in one year. The first aim of the thesis is to see whether Europe has achieved fiscal sustainability, whereas the second aim is to analyse the effects of Maastricht and the Stability and Growth Pact to this end. Another research aim is to present a formal fiscal sustainability assessment for the EU accession countries. Finally, the thesis bridges fiscal and external sustainability and studies the economy-wide sustainability separately in 'old' Europe and the accession countries. [Continues.

Forest habitats on the territory of the National Park „Central Balkan" Bulgaria

Identifaction and characterization of forest habitats on the territory of the "Central Balkan" National Park in Bulgaria was carried out. The national park is one of the most valuable and largest protected areas in Europe – second category according to the International Union for Conservation of Nature (IUCN). Based on 786 phytosociological relevés, a total of 17 different habitat types, according to EUNIS were identified and mapped. The habitats were ecologically characterized by Ellenberg indicator values and their area was determined. A comparison was made with the areas determined in previous works. The applied method is suitable for the purposes of managing protected territories and zones, for monitoring the status and especially the conservation status of the habitats. The results and especially the established new habitats support this point of view

The seed laser system of the FERMI free-electron laser: design, performance and near future upgrades

Abstract An important trend in extreme ultraviolet and soft X-ray free-electron laser (FEL) development in recent years has been the use of seeding by an external laser, aimed to improve the coherence and stability of the generated pulses. The high-gain harmonic generation seeding technique was first implemented at FERMI and provided FEL radiation with high coherence as well as intensity and wavelength stability comparable to table-top ultrafast lasers. At FERMI, the seed laser has another very important function: it is the source of external laser pulses used in pump–probe experiments allowing one to achieve a record-low timing jitter. This paper describes the design, performance and operational modes of the FERMI seed laser in both single- and double-cascade schemes. In addition, the planned upgrade of the system to meet the challenges of the upgrade to echo-enabled harmonic generation mode is presented

The COMIX polarimeter: a compact device for XUV polarization analysis

We report on the characterization of a novel extreme-ultraviolet polarimeter based on conical mirrors to simultaneously detect all the components of the electric field vector for extreme-ultraviolet radiation in the 45–90 eV energy range. The device has been characterized using a variable polarization source at the Elettra synchrotron, showing good performance in the ability to determine the radiation polarization. Furthermore, as a possible application of the device, Faraday spectroscopy and time-resolved experiments have been performed at the Fe M2,3-edge on an FeGd ferrimagnetic thin film using the FERMI free-electron laser source. The instrument is shown to be able to detect the small angular variation induced by an optical external stimulus on the polarization state of the light after interaction with magnetic thin film, making the device an appealing tool for magnetization dynamics research

Optical constants modelling in silicon nitride membrane transiently excited by EUV radiation.

We hereby report on a set of transient optical reflectivity and transmissivity measurements performed on silicon nitride thin membranes excited by extreme ultraviolet (EUV) radiation from a free electron laser (FEL). Experimental data were acquired as a function of the membrane thickness, FEL fluence and probe polarization. The time dependence of the refractive index, retrieved using Jones matrix formalism, encodes the dynamics of electron and lattice excitation following the FEL interaction. The observed dynamics are interpreted in the framework of a two temperature model, which permits to extract the relevant time scales and magnitudes of the processes. We also found that in order to explain the experimental data thermo-optical effects and inter-band filling must be phenomenologically added to the model

Towards jitter-free pump-probe measurements at seeded free electron laser facilities

X-ray free electron lasers (FEL) coupled with optical lasers have opened unprecedented opportunities for studying ultrafast dynamics in matter. The major challenge in pump-probe experiments using FEL and optical lasers is synchronizing the arrival time of the two pulses. Here we report a technique that benefits from the seeded-FEL scheme and uses the optical seed laser for nearly jitter-free pump-probe experiments. Timing jitter as small as 6 fs has been achieved and confirmed by measurements of FEL-induced transient reflectivity changes of Si3N4 using both collinear and non-collinear geometries. Planned improvements of the experimental set-up are expected to further reduce the timing jitter between the two pulses down to fs level

24 mJ Cr+4:forsterite four-stage master-oscillator power-amplifier laser system for high resolution mid-infrared spectroscopy

We present the design of a Cr:forsterite based single-frequency master-oscillator power-amplifier laser system delivering much higher output energy compared to previous literature reports. The system has four amplifying stages with two-pass configuration each, thus enabling the generation of 24 mJ output energy in the spectral region around 1262 nm. It is demonstrated that the presented Cr:forsterite amplifier preserves high spectral and pulse quality, allowing a straightforward energy scaling. This laser system is a promising tool for tunable nonlinear down-conversion to the mid-infrared spectral range and will be a key building block in a system for high-resolution muonic hydrogen spectroscopy in the 6.8 \u3bcm rang

Single shot time-resolved magnetic x-ray absorption at a Free Electron Laser

Ultrafast dynamics are generally investigated using stroboscopic pump-probe measurements, which characterize the sample properties for a single, specific time delay. These measurements are then repeated for a series of discrete time delays to reconstruct the overall time trace of the process. As a consequence, this approach is limited to the investigation of fully reversible phenomena. We recently introduced an off-axis zone plate based X-ray streaking technique, which overcomes this limitation by sampling the relaxation dynamics with a single femtosecond X-ray pulse streaked over a picosecond long time window. In this article we show that the X-ray absorption cross section can be employed as the contrast mechanism in this novel technique. We show that changes of the absorption cross section on the percent level can be resolved with this method. To this end we measure the ultrafast magnetization dynamics in CoDy alloy films. Investigating different chemical compositions and infrared pump fluences, we demonstrate the routine applicability of this technique. Probing in transmission the average magnetization dynamics of the entire film, our experimental findings indicate that the demagnetization time is independent of the specific infrared laser pump fluence. These results pave the way for the investigation of irreversible phenomena in a wide variety of scientific areas.Comment: 9 pages, 5 figure