Biomedical subjects
Publications and source records attributed to Gaetano Assanto.
Combining reverse proton exchange and uniform periodic poling in LiNbO3 planar waveguides, we demonstrate low-energy spatial optical solitons by second-harmonic generation at room temperature, with a threshold as low as 23 pJ/microm at 1.5 microm.
We investigate, for the first time to our knowledge, the discrete propagation of near-infrared light in a voltage-controlled array of channel waveguides in undoped nematic liquid crystals under planar anchoring conditions. This novel geometry enables us to drive the system from one-dimensional bulk diffraction to discrete propagation and, for larger excitations, to discrete spatial solitons, or nematicons. The observed phenomena are adequately described by a scalar model that encompasses the voltage-dependent reorientational response of the material.
We report on the observation and quantitative assessment of self-trapped pulsating beams in a highly nonlocal nonlinear regime. The experiments were conducted in nematic liquid crystals and allow a meaningful comparison with the prediction of a scalar theory in the perturbative limit, while addressing the need for beyond-paraxial analytical treatments.
The nonlocal nonlinearity stemming from molecular reorientation in nematic liquid crystals supports the formation of multiple solitary waves, following the onset of spatial modulational instability from both wide and focused input beams. We report experimental observations of such phenomena at power levels of hundreds of milliwatts in planar cells with a voltage bias.
We report the first observation of modulational instability in nematic liquid crystals encompassing a nonlocal behavior. The experimental results are quantitatively compared with the theory revealing the fundamental features associated to a nonlocal nonlinearity.
We develop a general theory of spatial solitons in a liquid crystalline medium exhibiting a nonlinearity with an arbitrary degree of effective nonlocality. The model accounts the observability of accessible solitons and establishes an important link with parametric solitons.
With second-harmonic generation in surface and buried planar waveguides achieved by direct and reverse proton exchange in lithium niobate, we demonstrate a novel kind of quadratic spatial simulton: The transverse-electric fundamental input and the transverse-magnetic second-harmonic waves nonlinearly couple two superimposed planar waveguides, permitting transverse localization of light at room temperature and at excitations as low as 340 nJ in 20-ps pulses.
Nematic liquid crystals exhibit a saturable, non-instantaneous nonlinear response through light-induced reorientation. In such a material, we demonstrate that (2+1)-dimensional spatial solitary waves can be generated at milliwatt power levels not only with a coherent optical beam, but also with incoherent excitations. Self-trapping also allows the efficient guidance of a weak co-polarized probe.
We review the theory of light localization due to the combined action of single or double Bragg coupling between dichromatic counterpropagating envelopes and parametric mixing nonlinearities. We discuss existence, stability, and excitation of such localized envelopes. We also investigate the link between stationary gap solitons and input-output response of nonlinear quadratic Bragg gratings. Frustrated transmission and multistable switching is expected to occur under suitable integrable (cascading) limits. Substantial deviations from these conditions lead to the onset of spatial chaos. (c) 2000 American Institute of Physics.