Thin Diamond Film on Silicon Substrates for Pressure Sensor Fabrication.

Thin polycrystalline diamond films chemically vapor deposited on thinned silicon substrates were used as membranes for pressure sensor fabrication by means of selective chemical etching of silicon. The sensing element is based on a simple low-finesse Fabry-Pérot (FP) interferometer. The FP cavity is defined by the end-face of a single mode fiber and the diamond diaphragm surface.

Temperature control of nematicon trajectories.

Using modulation theory, we develop a simple [(2+1)-dimensional] model to describe the synergy between the thermo-optical and reorientational responses of nematic liquid crystals to light beams to describe the routing of spatial optical solitary waves (nematicons) in such a uniaxial environment. Introducing several approximations based on the nonlocal physics of the material, we are able to predict the trajectories of nematicons and their angular steering with temperature, accounting for the energy exchange between the input beam and the medium through one-photon absorption. The theoretical results are then compared to experimental data from previous studies, showing excellent agreement.

Thermo-optic soliton routing in nematic liquid crystals: erratum.

This erratum amends some errors in Opt. Lett.43, 2296 (2018)OPLEDP0146-959210.

Optical Detection of Dangerous Road Conditions.

We demonstrated an optical method to evaluate the state of asphalt due to the presence of atmospheric agents using the measurement of the polarization/depolarization state of near infrared radiation. Different sensing geometries were studied to determine the most efficient ones in terms of performance, reliability and compactness. Our results showed that we could distinguish between a safe surface and three different dangerous surfaces, demonstrating the reliability and selectivity of the proposed approach and its suitability for implementing a sensor.

Interplay of Thermo-Optic and Reorientational Responses in Nematicon Generation.

Employing several nematic liquid crystal mixtures, we investigate how the thermo-optic response of nonlinear birefringent soft-matter affects the propagation of light beams and the features of self-induced waveguides. We address the formation of optical spatial solitons and the control of their trajectories versus temperature, comparing the measurements with the expectations based on a simplified model, showing an excellent agreement. Moreover, in a guest⁻host mixture with an absorbing dye dopant, we study the competition between reorientational and thermal nonlinearities, demonstrating that the two processes can be adjusted independently in order to tune the soliton properties, i.

Beaming random lasers with soliton control.

Random lasers are resonator-less light sources where feedback stems from recurrent scattering at the expense of spatial profile and directionality. Suitably-doped nematic liquid crystals can random lase when optically pumped near resonance(s); moreover, through molecular reorientation within the transparency region, they support self-guided optical spatial solitons, i.e.

Thermo-optic soliton routing in nematic liquid crystals.

We demonstrate thermo-optic control on the propagation of optical spatial solitons in nematic liquid crystals. By varying the sample temperature, both linear and nonlinear optical properties of the reorientational material are modulated by acting on the refractive indices, the birefringence, and the elastic response. As a result, both the trajectory and transverse confinement of spatial solitons can be adjusted, demonstrating an effective means to tune and readdress self-induced optical waveguides.

Nonlinear continuous-wave optical propagation in nematic liquid crystals: Interplay between reorientational and thermal effects.

We investigate nonlinear optical propagation of continuous-wave (CW) beams in bulk nematic liquid crystals. We thoroughly analyze the competing roles of reorientational and thermal nonlinearity with reference to self-focusing/defocusing and, eventually, the formation of nonlinear diffraction-free wavepackets, the so-called spatial optical solitons. To this extent we refer to dye-doped nematic liquid crystals in planar cells excited by a single CW beam in the highly nonlocal limit.

All-optical guided-wave random laser in nematic liquid crystals.

Spatial solitons can affect and enhance random lasing in optically-pumped dyedoped nematic liquid crystals. Upon launching two collinear beams in the sample, the first to pump the fluorescent guest molecules and the second to induce a reorientational soliton, strikingly the second beam not only guides the emitted photons in the soliton waveguide, but also enhances the lasing efficiency and modulates its spectral width. By altering the scattering paths of the emitted photons, the soliton also contributes to the selection of the lasing modes, as further confirmed by the observed kinks in the input/output characteristics.

Nonlinear competition in nematicon propagation.

We investigate the role of competing nonlinear responses in the formation and propagation of bright spatial solitons. We use nematic liquid crystals (NLCs) exhibiting both thermo-optic and reorientational nonlinearities with continuous-wave beams. In a suitably prepared dye-doped sample and dual beam collinear geometry, thermal heating in the visible affects reorientational self-focusing in the near infrared, altering light propagation and self-trapping.

Nematicons in planar cells subject to the optical Fréedericksz threshold.

We investigate, both theoretically and experimentally, self-trapping of light beams in nematic liquid crystals arranged so as to exhibit the optical Fréedericksz transition in planar cells. The resulting threshold in the nonlinear reorientational response supports a bistable behavior between diffracting and self-localized beam states, leading to the appearance of a hysteretic loop versus input excitation. Our results confirm the role of nematic liquid crystals in the study of non-perturbative nonlinear photonics.

Power-controlled transition from standard to negative refraction in reorientational soft matter.

Refraction at a dielectric interface can take an anomalous character in anisotropic crystals, when light is negatively refracted with incident and refracted beams emerging on the same side of the interface normal. In soft matter subject to reorientation, such as nematic liquid crystals, the nonlinear interaction with light allows tuning of the optical properties. We demonstrate that in such material a beam of light can experience either positive or negative refraction depending on input power, as it can alter the spatial distribution of the optic axis and, in turn, the direction of the energy flow when traveling across an interface.

Beam hysteresis via reorientational self-focusing.

We theoretically investigate light self-trapping in nonlinear dielectrics with a reorientational response subject to threshold, specifically nematic liquid crystals. Beyond a finite excitation, two solitary waves exist for any given power, with an hysteretic dynamics due to feedback between beam size, self-focusing and the nonlinear threshold. Soliton stability is discussed on the basis of the system free energy.

Bistability with optical beams propagating in a reorientational medium.

We investigated bistability with light beams in reorientational nematic liquid crystals. For a range of input powers, beams can propagate as either diffracting or self-trapped, the latter corresponding to spatial solitons. The first-order transition in samples exhibiting abrupt self-focusing with a threshold is in agreement with a simple model.

Nematicons and their electro-optic control: light localization and signal readdressing via reorientation in liquid crystals.

Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely "nematicons". Nematicons can guide other light signals and interact with inhomogeneities and other beams.

Nematicon-nematicon interactions in a medium with tunable nonlinearity and fixed nonlocality.

We investigate the attractive interaction between spatial solitons in nematic liquid crystals with a tunable nonlinearity and a constant nonlocality. The experimental study, carried out by controlling the orientation of the optic axis via the electro-optic response, shows how the interactions depend on reorientation, in excellent agreement with a model accounting for the anisotropic nature of the dielectric.

Self-turning self-confined light beams in guest-host media.

We demonstrate power-dependent steering of self-confined light beams propagating in the nonparaxial regime in a guest-host nonlinear medium. Exploiting the Janossy enhancement in dye-doped liquid crystals with reorientational response, we observe sub-mW spatial soliton self-steering as large as 39 degrees, accompanied by trapping of the light spontaneously emitted by the excited dye. The self-turning is modeled in terms of an effective transverse force stemming from the longitudinal electric field in the tightly confined beams, with good agreement between data and simulations.

Nonlinearly controlled angular momentum of soliton clusters.

We demonstrate an original approach, to the best of our knowledge, to acquire nonlinear control over the angular momentum of a cluster of solitary waves. We show that the angular momentum can be adjusted by acting on the global excitation of the system. The effect is verified in liquid crystals by observing power-dependent rotation of a two-soliton cluster.