This is the website of the Laboratory of Nonlinear Photonics and Theoretical Physics at the Department of Physics of the University Sapienza. Our program is applying paradigms from the science of complex systems to light propagation, and investigating the development of complexity and self-organization in nonlinear waves. We want to test and deepen ideas of fundamental physics by using optics and photonics, and developing experiments, high performance computing approaches, and theory.
Nonlinear Optomechanical Pressure and Graphene
The mechanical effect of light has been the subject of the investigations of many scientists for more than three centuries but many questions are still open. In a recent manuscript (arXiv.org:1403.1948), C. Conti and Robert W. Boyd predict that high energy ultrashort laser pulses may mechanically attract an object.
The effect is due to the fact that the velocity of a photon depends on the laser intensity. Because of the momentum conservation, also the velocity of an optically pushed object depends on the light intensity; hence the mechanical action of light can be all-optically controlled. This may be denoted to as the Nonlinear Balazs Block problem.
By using this nonlinear optical effect it may be possible to design experiments in which objects are attracted or accelerated by short pulses by an amount determined by pulse energy, temporal duration and spectral content. This nonlinear mechanical action is due to a property common to any sufficiently transparent material, the optical Kerr effect, that is, an intensity dependent refractive index. Conti and Boyd consider the specific case of a thin membrane of graphene, which has a very pronounced optical Kerr effect, and predict that is may be deformed as an optical sail by light. This may have a variety of applications for laser propulsion, and for laser controlled shaping of surfaces.
The authors report a theoretical analysis, which is validated by first principles simulations of the 3D+1 nonlinear Maxwell equations by using High Performance Computing (HPC) facilities within the CINECA-ISCRA initiative.
Last Updated (Tuesday, 11 March 2014 09:35)
Nonlocality and dissipation due to non-paraxiality
The investigation of nonlinear optical propagation in extreme regimes is one of the frontiers of modern research.
Generally speaking, beyond the usual approximations, one could expect just small perturbations to known effects, as diffraction, solitons, and self-phase modulation; however, in specific cases, novel phenomena arise.
One relevant example is given by the breaking of the paraxial approximation. In a paper published in the Physical Review A, (arXiv:1402.1161) Nicola Bulso and Claudio Conti theoretically and numerically show that non-paraxial propagation in a simple local Kerr medium may produce effective dissipation and nonlocality even if no loss mechanism is present. This radically affects well known processes as modulational instability and soliton propagation.
The picture below shows the evolution of an higher order soliton when including non-paraxiality in different theoretical models.
Last Updated (Friday, 07 February 2014 05:05)
Optical Shock Waves in Silica Areogel
Silica Areogel is a material that is mostly composed by air. A tiny silica scaffold forms samples that have unique physical properties with an enormous amount of applications. Also the nonlinear optical properties and, in particular, the thermally driven features, are very surprising and in several respects are unknown.
In a paper published in Optics Express, S. Gentilini, F. Ghajeri, N. Ghofraniha, A. Di Falco, and C. Conti, report on the experimental observation of wave-breaking phenomena in these materials, very promising because they can sustain high power continuous wave irradiation without boiling and melting. The samples have been realized by A. Di Falco and F. Ghajeri.
This is another remarkable example of shock waves in disordered media. The picture below shows the areogel sample.
Last Updated (Saturday, 18 January 2014 07:12)
Anderson localization with a purely nonlinear origin
Anderson localization concerns the transition to a regime in which all the modes of a disordered system are exponentially localized. It also often and generically refers to wave-localizations in a disordered potential.
In general the potential that induces these states is linear; but one may argue if, in a linearly homogeneous medium, localizations may arise from a random modulation of the nonlinear response. This is what Viola Folli, Katia Gallo and Claudio Conti investigate in a paper published in Optics Letters.
It turns out that disorder-induced localized states may have a purely nonlinear origin, but this is accompanied by instability processes that amplify the Anderson states and lead to complicated nonlinear dynamics, still un-explored. An example is given in the process of parametric down-conversion in periodically poled crystals for optical second harmonic generation (picture below).
A notable property of purely nonlinear Anderson states is the fact that their localization length is determined by the input power.
Last Updated (Friday, 06 December 2013 20:44)