Conical waves in nonlinear optics and applications.

The quest for light has always challenged man and constitutes one of our fundamental activity since the dawn of conscience. Being at the base of our perception of the world, the presence of light and the intelligence of our surroundings are always linked: since the prehistoric era man felt the need to produce that light which could keep him in the adequate condition to percept the ambient. Accompanied by firelights, oil lamps, wax candles and electric bulbs, man encountered a crescendo of possibility to extend his capability to stay active and clever in front of reality. The ultimate light source shining in the hands of man was invented in the fifties by Charles H. Townes: the possibility to use coherent laser light constituted a revolution in this challenge and since that moment an extremely wide horizon of phenomena began to be accessible to the perception of our eyes. Beyond new horizons of perception, laser sources extended the use of light as a tool for matter manipulation with results previously impossible to achieve, so that our everyday life is now filled with devices based and realized with laser technology. This goal has been achieved because the interaction between laser light and matter ranges in a surprisingly wider extent than the simple heating. One of the dreams in this challenge, is to obtain a light packet perfectly controllable and solid in the interaction with matter which could act as a light particle or bullet. This work is inserted in this challenge, and collects a variety of experiences and observations suggesting new perspectives for this hunt. The results I obtained during these last three years of research are intrinsically linked to the method and idea of knowledge proposed by professor Paolo Di Trapani. My work takes advantage of the experience and skill of several people coming from different corners of the world, joined by a fruitful friendship in the adventure of contemporary research. The common scientific interest of this crew is the physics of nonlinear conical waves, which are particular wave packets with more complex spectral structure than the familiar Gaussian laser pulse. The history of the conquer of this precious conceptual tool by the members of the VINO team is not trivial and gathers contributions from several events. My wish was to exploit these waves as tools for possible applications, and a consistent part of the present dissertation relies on this will. On the other hand I was also witness of other important unpredicted experiences all reported in this dissertation. The exposition of my work can’t follow the chronological flow of the events, since I have to choose a more conceptual narration to keep a higher degree of comprehension for the reader. This thesis begins with the introduction in the first chapter of some basic modeling tools of nonlinear optics phenomena which can be found on several books. At the end of this chapter I devote some space to the light soliton which is a nonlinear wave relying on the usual Gaussian approach of laser phenomena. Actually this is not the theme of my research, which is rather an escape from this approach. In the second chapter I introduce monochromatic conical waves as a first fugue from this theme. Chapter three and four exploit in detail my research on this waves. Chapter five introduces polychromatic conical waves and refers to their spontaneous formation in filamentation of ultrashort pulses. In chapter six I will enter in the details of different phenomena observed in filamentation processes; ironically my thesis ends in chapter seven reporting the first ever observed two dimensional stable soliton propagating in bulk media.