Isidro Villó-Pérez

In this work, we introduce a new concept of plasmonic nanoantenna: the Hydrodynamic Nano-Dipole Antenna (HNDA), based on the hydrodynamic model of the electron gas. Conventional optical plasmonic antennas, typically studied within the local Drude approximation, can concentrate and manipulate light by coupling incident radiation to localized surface plasmon resonances in metallic nanostructures. In contrast, our approach is based on the excitation of bulk plasmons as propagating modes. These bulk modes are longitudinal in nature, originate from the nonlocality of the hydrodynamic model, and offer new possibilities for signal transmission at the nanoscale. Our study provides closed-form solutions for the potential, electric field, and induced charge under time-harmonic monopole and dipole excitations. Special attention is given to nanoantennas of length l=nλ/2, for which directional far-field radiation patterns are derived and analyzed. Using material parameters for doped indium antimonide (InSb), we demonstrate the feasibility of such antennas operating in the terahertz (THz) regime. Overall, these results establish the HNDA both as a new theoretical paradigm in nonlocal plasmonics and as a practical building block for THz nanophotonics, with potential applications in compact spectroscopy, on-chip communications, and active nanodevices.

Acoustic leaky-wave antennas (ALWAs) have demonstrated the capacity to steer directive sound waves in frequency-dependent directions, due to the inherent dispersive radiation characteristic of leaky modes. Compared to more conventional uniform linear array (ULA) acoustic traducers for electronic beam steering (which rely on multiple sensors), the ALWA allows for single microphone operation. Thus, ALWAs offer a direct mechanism to scan a directive acoustic beam in the angular space by simply sweeping the operating frequency of the acoustic signal, which envisions cost-efficient single-transducer direction finders for SONAR applications. In this paper, we study for the first time some important features of an ALWA for acoustic underwater Direction-of-Arrival (DoA) estimation applications. First, we report for the first time on the necessity to shape the radiated ALWA beams in both far- and near-field zones to improve the DoA estimation performance, following similar techniques recently applied for low-cost frequency-scanned direction-finding radars based on LWAs. Furthermore, the capacity to reduce the Side Lobe Level (SLL) has been analyzed in order to improve performance, demonstrating aperture tapering techniques to the ALWA for the first time. These acoustic behaviour aspects have a considerable interest in real applications of ALWA in innovative SONAR systems for underwater scenarios.

For years, in the field of underwater acoustics, a line of research with special relevance for applications of environmental monitoring and maritime security has been developed that explores the possibilities of non-linear phenomena of sound propagation, especially referring to the so-called parametric effect or self-modulation. This article shows the results of using a new modulation technique based on sine-sweep signals, compared to classical modulations (FSK and PSK). For each of these modulations, a series of 16-bit strings of information with different frequencies and durations have been performed, with the same 200 kHz carrier wave. All of them have been tested in the Hydroacoustic Laboratory of the CTN and, through the application of cross-correlation processing, the limitations and improvements of this novel processing technique have been evaluated. This allows reaching better limits in discrimination of bits and signal-to-noise ratio used in underwater parametric acoustic communications.

The detection of faint stellar companions requires high contrast techniques such as coronagraphy. To achieve such high contrast coronagraphs must work with the aid of adaptive optics or be mounted on space telescopes. We propose a new coronagraphic technique that consists of the digital processing of non-coronagraphic images. The only requirement is a priori knowledge of the telescope amplitude point spread function. This digital coronagraph algorithm presents the advantage that it avoids problems associated with manufacture, implementation, and alignment of optical coronagraphs. The digital coronagraph algorithm is successfully checked with laboratory generated images. Moreover, numerical simulations show that the digital coronagraph presents contrast curves similar to that of the optical coronagraph. Finally, speckle noise can be cancelled out as effectively as in optical coronagraphs.

Adaptive Optics Lucky Imager (AOLI) is a state-of-the-art instrument that combines adaptive optics (AO) and lucky imaging (LI) with the objective of obtaining diffraction-limited images in visible wavelength at mid- and big-size ground-based telescopes. The key innovation of AOLI is the development and use of the new Two Pupil Plane Positions Wavefront Sensor (TP3-WFS). The TP3-WFS, working in visible band, represents an advance over classical wavefront sensors such as the Shack-Hartmann WFS because it can theoretically use fainter natural reference stars, which would ultimately provide better sky coverages to AO instruments using this newer sensor. This paper describes the software, algorithms and procedures that enabled AOLI to become the first astronomical instrument performing real-time AO corrections in a telescope with this new type of WFS, including the first control-related results at the William Herschel Telescope.