Research is conducted with a common goal: understanding the mechanism underlying spontaneous transformation of high intensity laser pulses into Conical Waves.
This idea is based on the observation that conical beams or pulses, that is pulses in which the energy flows along the surface of a cone continuously refilling a central intensity spike, appear as a common factor in many physical systems.
From this study, a number of applications emerge, where conical waves outperform conventional laser beams in optical technologies.
Conical Waves therefore become a new tool with which to interpret complex physical systems and also a tool for new applications in nonlinear optics.
Modulational Instability (MI), i.e. the growth of noise at certain spatio-temporal frequencies within a laser pulse destroys stationarity or self-similar propagation and leads to the break-up of the pulse. However it is also the moving force that enables the manifestation of new stationary states that therefore form spontaneously in the nonlinear medium. The most well known example in this sense is MI in optical fibers that leads to a temporal breakup of a Gaussian-like pulse into much shorter pulses, precursors of one-dimensional optical solitons. Moving into three-dimensional systems the physics are slightly more complicated but, in a similar fashion to the 1D case, MI may explain the spontaneous pulse splitting and formation of stationary X waves characteristic of ultrashort laser pulse filamentation in condensed Kerr media.
Ultrashort laser pulse filamentation is a topic of great interest and may give rise to a number of applications. Studying the spontaneous evolution of light filaments in condensed media we have highlighted the spontaneous formation of so-called X waves, a class of stationary wave packets. Under the assumption that the laser pulse as whole propagates as an X wave it is possible to reinterpret many aspect s of the filamentation process (such as conical emission, axial supercontinuum generation, pulse splitting etc.) with a single and simple model. Using the same approach it is possible to predict the behavior of a weak seed pulse in the presence of an intense filament, its modification due to various nonlinear processes ranging from Four-Wave-Mixing to Stimulated Raman Scattering.
Bessel Beams and pulses are the simplest and most common example of the conical wave and may be easily generated in any lab. For this reason most application proposals start from the Bessel beam: these range from waveguide writing in various materials to excitation of nonlinearities over a large focal depth. Fundamental studies are also underway considering the possibility to excite a new class of stationary states whose stationarity is sustained (rather than inhibited) by nonlinear losses.
Parametric downconversion of ultrashort laser pulses leads to a strong space-time coupling. Studying the Quantum and coherence properties of this coupling and using the paradigm of conical waves and the diagnostic tools developed in the other research areas, it is possible to highlight new unexpected features of this process.
