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Centre for "Studies and Training in Experiments with Lasers and Laser Applications"

Final Activity Report Summary - STELLA (Centre for "Studies and Training in Experiments with Lasers and Laser Applications")

STELLA has proposed to the scientific community a renewed understanding of non-linear optics, based on the concept of nonlinear conical waves. These are unique wave packets, whose intense localised peak penetrates deeply into and transfers energy to matter, or to other waves, without suffering attenuation, diffraction or dispersion. Several among the main nonlinear optical phenomena, e.g. parametric amplification, second harmonic, Raman and white-light continuum generation, spatial, temporal and spatiotemporal instabilities, beam break up, pulse splitting and shock-front formation, cross-phase modulation, four-wave mixing, conical emission, ultrashort pulse filamentation in liquids, solids, gases and semiconductors, have been re-interpreted, in a unified scenario, in terms of conical waves, with an evident gain in understanding and prediction capability. As to applications, 'plasma wires' of unbeatable reproducibility, length, and uniformity were excited by conical wave pumping in gas media, and the approach was exploited to generate fs THz pulses 50 % shorter than those obtained by usual Gaussian beams.

Moreover, the first large-aperture Kerr-driven optical parametric amplifier was developed, whose inherent spatial instability has been hindered relying upon the stability properties of the conical waves. In the extreme ultraviolet (EUV) regime, incomparable large phase-matching lengths for selected harmonics have been found in case of pumping by conical waves, and experiments are currently hunting for a conversion efficiency a few order of magnitude higher than what obtainable by means of Gaussian beams.

STELLA_SCHOOL, i.e. the 'School for Training in Experiments with Lasers and Laser Applications', is the first ever summer school in laser physics and nonlinear optics where highly qualified training in experimental techniques is delivered directly on top-level research equipment. The event, participated by about 25 students and researchers per year, has been hosted by the Laser Research Centre in Vilnius (2007), by the FORTH Institute of Electronic Structure and Lasers in Heraklion (2008) and by and the ICFO Institute for Photonic Sciences in Barcelona (2009), which were putting rooms, equipment, teaching staff and technical personnel at students' disposal for the outlined training purpose. Besides the experimental courses delivered by world leading scientist on their latest achievements, several original experiments have been also performed by students and teachers at the school labs, whose results led to a number of publications. The school has provided a unique opportunity for a large team of younger and senior experimentalists and theoreticians to work together at well-defined scientific problem.

STELLA_LIGHT has proposed 'Light in light', a broad-audience theatrical performance about light and knowledge. By using water suspensions of glass nanospheres for reproducing atmospheric light scattering over underwater landscapes, laser beams for sun rays, plexiglas spheres and water jets for rain droplets, and also trees, pergolas, shading clouds etc., a number of spectacular optical atmospheric phenomena were carefully reconstructed indoor: the light and colour of the sky, of the sun, and of the shade, in clear of foggy days, during sunset or storm, and the rainbow, as well as many other events related to the direct, reflected, scattered or diffracted vision of the sun.

By comparing these reconstructions with those presented in fine-art pictures, photos, cinema, architecture, and poetry about light, visitors were surprisingly brought to the discovery of how much science might help in disclosing the connection existing between art and everyday experience of light. The exhibition, which comprised 1 200 square meters of installations in 7 rooms, operated with up to 36 itinerant 1h 45m performances per day, being visited by more than 15 000 people during the three-weak opening time.