Biomedical subjects

E Santamato

Publications and source records attributed to E Santamato.

15 recordsLinked to original sources

PubMed2006

Nonlinear dynamics induced in liquid crystals in the presence of the orbital and spin angular momentum of light.

We studied the dynamical effects induced in a homeotropic nematic film when a normally incident circularly polarized light beam with an elliptical intensity profile is used. A three-dimensional dynamical model shows that, besides the spin, the orbital angular momentum of photons also plays a role in the reorientation process. Our measurements fairly reproduce the main dynamical features predicted by the model in the near threshold region. The model, however, does not work, as it is, at higher incident laser power where chaotic director rotation was reported [A. Vella, A. Setaro, B. Piccirillo, E. Santamato, Phys. Rev. E 67, 051704 (2003)].

Journal Article↗

PubMed2003

On-off intermittency in chaotic rotation induced in liquid crystals by competition between spin and orbital angular momentum of light.

We observed on-off intermittency in the chaotic rotation induced by a cw laser beam in a thin liquid crystal film where the spin and the orbital angular momentum of light compete in reorienting the sample. We found that the azimuthal angle phi(t) of the molecular director increased linearly in time on large time scales but, occasionally, it exhibited large fluctuations about its average value omega(0)t, so that its angular velocity phi;(t) undergoes an on-off intermittent motion. The intermittent signal omega(t)=phi;(t)-omega(0) obeyed the scaling laws of on-off intermittency, including the symmetry between laminar and burst phases. The chaotic rotations were observed only when the spin and the angular momentum of light were transferred simultaneously to the sample.

Journal Article↗

PubMed2002

Coupled-mode approach to the nonlinear dynamics induced by an elliptically polarized laser field in liquid crystals at normal incidence.

A coupled-mode theory is presented to describe the dynamics of the molecular director induced by an elliptically polarized light plane wave normally incident onto a homeotropic liquid crystal film. The model provides a set of time ordinary differential equations for the lowest two modes of the system while the influence of the higher-order twist modes is accounted for by means of the adiabatic approximation. The resulting dynamics is complex above the reorientation threshold, according to the intensity and polarization of the incident light, rotating, oscillating, or steady states may settle. The dynamical regimes have been studied as functions of external parameters. The agreement with the experimental data was very good.

Journal Article↗

PubMed2001

Orbital and spin photon angular momentum transfer in liquid crystals.

All-optical angular control of the molecular alignment in liquid-crystal films is demonstrated using a laser beam having an elliptically shaped intensity profile. The material birefringence is unimportant, as proven by the fact that good alignment is obtained with unpolarized light. This raises the possibility of achieving optical angular control of transparent isotropic bodies. A general theoretical approach, based on light and matter angular momentum conservation, shows that the optical alignment is due to the internal compensation between the transfer of the orbital and the spin part of angular momentum of the incident photons to the material.

Journal Article↗

PubMed1995