Directional dependence of the second harmonic response in two-dimensional nonlinear photonic crystals

The following article appeared in Applied Physics Letters 96.26 (2010): 261111 and may be found at https://aip.scitation.org/doi/10.1063/1.3459975A two-dimensional periodic arrangement of alternating ferroelectric domains in LiNbO3, with asymmetric domain duty cycle has been used to demonstrate that counterpropagating beams along the polar axis can generate disparate second harmonic patterns, which are nonsymmetrical with respect to the source and the point of observation. These findings provide alternative routes to generate dissimilar light-matter interaction processes in two-dimensional structures assembled onto polar surfaces, including metals for plasmonics or biological compound

Selective rearrangement of Nd3+ centers in LiNbO3 under ferroelectric domain inversion by electron beam writing

The following article appeared in Physical Review B - Condensed Matter and Materials Physics 78.1 (2008): 014114 and may be found at https://journals.aps.org/prb/abstract/10.1103/PhysRevB.78.014114Different values of the electronic charge provided by a direct electron beam writing system have been used to produce polarization inverted domain regions in the micrometer range on Nd3+ optically activated LiNbO3. The effect of the electronic charge on the Nd3+ center structure has been studied by means of low-temperature luminescence from Nd3+ ions. The axial crystal field acting on the Nd3+ centers has been analyzed through the F4 3/2 energy-level splitting of the Nd3+ ions. From there we have determined the position of Nd3+ ions into the Li+ octahedra for the different unequivalent centers in domains reversed with different electronic doses. The results show that the axial crystal field acting on the unequivalent Nd3+ centers can be selectively modified by means of the different doses applied to produce the inversion of the polarization. Moreover, a control of the discrete shifts suffered by the Nd3+ ions into the Li+ octahedra after the inversion process can be carried out in the range 0-0.02Å by selecting the type of Nd center to be shifted by means of the different electronic charge. The behavior of each Nd3+ center after the polarization inversion under different doses can be discriminated and the different nature, as well as the polar character of the Nd3+ centers, is clearly manifeste

Silver nanoparticle chains for ultra-long-range plasmonic waveguides for Nd3+ fluorescence

Plasmonic waveguides have been shown to be a promising approach to confine and transport electromagnetic energy beyond the diffraction limit. However, ohmic losses generally prevent their integration at micrometric or millimetric scales. Here, we present a gain-compensated plasmonic waveguide based on the integration of linear chains of Ag nanoparticles on an optically active Nd3+-doped solid-state gain medium. By means of dual confocal fluorescence microscopy, we demonstrate long-range optical energy propagation due to the near-field coupling between the plasmonic nanostructures and the Nd3+ ions. The subwavelength fluorescence guiding is monitored at distances of around 100 µm from the excitation source for two different emission ranges centered at around 900 nm and 1080 nm. In both cases, the guided fluorescence exhibits a strong polarization dependence, consistent with the polarization behavior of the plasmon resonance supported by the chain. The experimental results are interpreted through numerical simulations in quasi-infinite long chains, which corroborate the propagation features of the Ag nanoparticle chains at both excitation (λexc = 590 nm) and emission wavelengths. The obtained results exceed by an order of magnitude that of previous reports on electromagnetic energy transport using linear plasmonic chains. The work points out the potential of combining Ag nanoparticle chains with a small interparticle distance (~2 nm) with rare-earth-based optical gain media as ultra-long-range waveguides with extreme light confinement. The results offer new perspectives for the design of integrated hybrid plasmonic–photonic circuits based on rare-earth-activated solid-state platformsThis research has been funded by the Spanish State Research Agency under contracts PID2019-108257GB-I00 and RTI2018-098452-B-100, Comunidad de Madrid under contract CAM (SI1/PJI/2019-00105) and the María de Maeztu “Programme for Units of Excellence in R&D” CEX2018-000805-

Nd3+ ion shift under domain inversion by electron beam writing in LiNb O3

The following article appeared in Applied Physics Letters 90.14 (2007): 141901 and may be found at https://aip.scitation.org/doi/10.1063/1.2719036Ferroelectric domain inversion has been obtained in Nd3+ doped lithium niobate by means of direct electron beam writing. The local effects of the polarization inversion on the optical transitions of Nd3+ ions have been studied by low temperature high resolution site selective spectroscopy. Inverted regions present different axial crystal field acting over Nd3+ ions compared with noninverted (original) regions. The results can be interpreted in terms of slight shifts of Nd3+ ions along the ferroelectric c axis within the Li+ octahedrons, as a result of the lattice rearrangement after the domain inversion processe

Coupling Nd3+:Y2O3 fluorescent submicron particles to linear plasmonic chains

We report on the fabrication and optical characterization of a new hybrid material consisting of Nd3+ doped Y2O3 submicron particles associated with linear chains of plasmonic nanostructures. By drop-casting deposition, single Nd3+ doped Y2O3 polycrystalline particles are dispersed and located in the vicinities of plasmonic chains of silver nanoparticles formed on the surface a LiNbO3 substrate. The interaction between the plasmonic modes of the chain with the fluorescent yttria submicron particles is analyzed by micro-luminescence experiments. Orthogonal polarization configurations of the excitation radiation, namely, perpendicular and parallel to plasmonic chain axis, are employed to study the effect of the longitudinal and transverse chain plasmonic modes on the luminescence of the particles. A remarkable dependence of the emission intensity of the Nd3+:Y2O3 submicron particles on the excitation polarization is observed, showing the capability of plasmonic chains to modulate the emission of fluorescent submicron particles in contact with the chain. Numerical simulations evidence a different distribution of the excitation radiation field within the Nd3+:Y2O3 particle depending on the type of excited plasmonic mode, longitudinal or transversal, of the chain, and hence, the ability of plasmonic chains for controlling the emission of Rare Earth doped submicron particlesThis work has been supported by the Spanish State Research Agency under contracts PID2019-108257GB-I00, PID2022-137444NB-I00 and the María de Maeztu “Programme for Units of Excellence in R&D″ CEX2018-000805-M. P.G acknowledges funding from the French Agence Nationale de la Recherche under grant ANR-20-CE09-0022 (UltraNanOSpec

Integrating 2D materials and plasmonics on lithium niobate platforms for pulsed laser operation at the nanoscale

The current need for coherent light sources for integrated (nano)photonics motivates the search for novel laser designs emitting at technologically relevant wavelengths with high-frequency stability and low power consumption. Here, a new monolithic architecture that integrates monolayer MoS2 and chains of silver nanoparticles on a rare-earth (Nd3+) doped LiNbO3 platform is developed to demonstrate Q-switched lasing operation at the nanoscale. The localized surface plasmons provided by the nanoparticle chains spatially confine the gain generated by Nd3+ ions at subwavelength scales, and large-area monolayer MoS2 acts as saturable absorber. As a result, an ultra-compact coherent pulsed light source delivering stable train pulses with repetition rates of hundreds of kHz and pulse duration of 1 µs is demonstrated without the need of any voltage-driven optical modulation. Moreover, the monolithic integration of the different elements is achieved without sophisticated processing, and it is compatible with LiNbO3-based photonics. The results highlight the robustness of the approach, which can be extended to other 2D materials and solid-state gain media. Potential applications in communications, quantum computing, or ultra-sensitive sensing can benefit from the synergy of the materials involved in this approach, which provides a wealth of opportunities for light control at reduced scalesPID2019-108257GB-I00, PID2022-137444NB-I0, CEX2018-000805-M, PID2019-106268GB-C3

SBN y LiNbO3 como dispositivos multifuncionales de ganancia|bpropiedades ópticas y experimentos en cavidad

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de los materiales. Fecha de lectura: 28-10-200