Roberto Caputo

Università della Calabria | Università della Calabria · Department of Physics

Thanks to an optimized nanostructures arrangement , we report on temperature variation of 250 • C by impinging a plasmonic device with a green laser radiation. This great temperature value is caused by the strong confinement of electric field that is due to the covering gold nano heaters with a layer of polymer + dye. A chopper-modulated impinging...

An increasing amount of research is being devoted to improve the spatial resolution in direct laser writing (DLW) technique allowing the fabrication of complex 2D and 3D nanoscale devices. Among the various possibilities, we exploited uncommon features as extraordinary transmittance, zero re ectance, giant dephasing and epsilon-near-zero relative p...

Dielectric singularities (DSs) constitute one of the most exotic features occurring in the effective permittivity of artificial multilayers called hyperbolic metamaterials (HMMs). Associated to DSs, a rich phenomenology arises that justifies the ever-increasing interest profuse by the photonic community in achieving an active control of their prope...

Metamaterials are artificial electromagnetic media structured on the sub-wavelength scale for controlling the propagation of waves by means of transformation optics. The research activity is now focusing on attaining active metamaterial functionalities, including tunability, and the shaping and modulation of electromagnetic waves. Among all the dif...

In this contribution, a metal/insulator/metal/insulator (MIMI) metamaterial upgrades a standard two- photon direct laser writing process to hyper resolution thanks to its uncommon feature as extraordinary transmittance, zero reflectance and epsilon-near-zero permittivity. The voxel size reduction of about 89% height and 50% width allows fabrication...

Dielectric Singularities (DSs) constitute one of the most exotic features occurring in the effective permittivity of artificial multilayers called Hyperbolic Metamaterials (HMMs). Associated to DSs, a rich phenomenology arises that justifies the ever-increasing interest profuse by the photonic community in achieving an active control of their prope...

Various systems based on nanostructures built on optical waveguides have recently appeared in literature, since this configuration guarantees an efficient optical feeding to nano-elements and/or the possibility to manipulate guided signals. In this work, we present the analysis of the optical scattering properties of such type of structures, more s...

Multilevel anticounterfeiting Physical Unclonable Function (PUF) tags based on thin film of silver (Ag), Zinc Oxide (ZnO) and PolyVinylPyrrolidone (PVP), are experimentally demonstrated and validated. We exploit the low adhesion of silver to glass and consequent degradation during ZnO deposition to induce morphological randomness. Several photograp...

We experimentally demonstrate the possibility to modulate the second harmonic power emitted by nonlinear AlGaAs metasurfaces embedded in a liquid crystal (LC) matrix. This result is obtained by changing the relative in-plane orientation between the LC director and the linear polarization of the light at the excitation wavelength. According to numer...

Superhydrophobic surfaces coupling with photothermal effect, as a passive solution independent of external energy input, have shown promising perspectives for anti-icing and deicing. However, most hydrophobic photothermal materials are costly and require complicated fabrication processes, which limit their development in large-scale applications. H...

Photothermal superhydrophobic coatings are essential for a variety of applications including anti‐icing and light‐driven self‐propelled motion. However, achieving a flexible and durable superhydrophobic coating with high photothermal efficiency and long‐term stability is still challenging. Herein, a facile and eco‐friendly approach to realizing a s...

The coupling of gold nanoantennas (AuNAs) in the arrangement of monomers in bidimensional gratings is investigated both experimentally and numerically. The influence of edge diffraction, corresponding to the grazing propagation of specific diffracted orders, and the dependence of grating parameters on lattice plasmon modes are studied. It is shown...

Hybrid Flatland Metastructures is a comprehensive reference covering the latest developments in the field of metamaterials. It addresses fundamental concepts, physical considerations, and state-of-the-art applications. Topics covered in this book are carefully selected to be both representative and demonstrative of recent achievements in hybrid fla...

Plasmonic nanoheaters are reported that produce a significant local heating when excited by a 532 nm wavelength focused laser beam. A significant temperature increase derives from the strong confinement of electric field enabled by the specific arrangement of Au nanodisks constituting the nanoheater. The thermal response is much more sensitive when...

We experimentally investigate the photothermal conversion in disordered silicon nanowires (SiNWs) grown on a glass substrate by plasma-enhanced chemical vapor deposition. The temporal and spatial response under illumination of a 532 nm laser has been measured by means of an infrared (IR) thermocamera. Fast heat generation and adjustable temperature...

Plasmonic nanoheaters are reported that produce a significant local heating when excited by a 532 nm wavelength focussed laser beam. A significant temperature increase derives from the strong confinement of electric field enabled by the specific arrangement of Au nanodisks constituting the nanoheater. The thermal response is much more sensitive whe...

A novel technique is developed to improve the resolution of two‐photon direct laser writing lithography. Thanks to the high collimation enabled by extraordinary εNZ (near‐zero) metamaterial features, ultrathin dielectric hyper‐resolute nanostructures are within reach. With respect to the standard direct laser writing approach, a size reduction of 8...

DESCRIPTION Two-photon direct laser writing (TP-DLW) is widely used in stereolithographic processes for realizing sophisticated micro- and nanoscale structures with application in fluidics, photonics, and biomedical devices. In this chapter, it is detailed how leveraging on metal-dielectric metastructures with peculiar optical functionalities is po...

DESCRIPTION In the last 20 years, metamaterials have attracted much attention for their exotic physical behaviors not commonly present in nature. However, this class of micro- and nanostructured artificial media, characterized by groundbreaking electromagnetic and photonic properties, has encountered difficulty in entering industrial upscale and en...

DESCRIPTION Plasmonic nanostructures show outstanding promise in allowing sensitive temperature control, due to their natural ability to strongly confine a nanoscale electric field and release heat. In this chapter, the evolution of thermoresponsive metastructures is described from their introduction as amorphous arrangements of homogeneously distr...

DESCRIPTION This chapter considers hybrid metastructures operating in waveguide configuration. This configuration can unlock unprecedented functionalities when the interplay between quantum emitters and plasmonic nanostructures is efficiently exploited. The chapter begins with an introduction of the Purcell effect responsible for the emission enhan...

Confining near-infrared (NIR) and mid-infrared (MIR) radiation (1−10 μm) at the nanoscale is one of the main challenges in photonics. Thanks to the transparency of silicon in the NIR-MIR range, optoelectronic systems like electro-optical modulators have been broadly designed in this range. However, the trade-off between energy-per-bit consumption a...

Gold nanoparticle arrangements are identified as plasmonic heaters due to the photo-thermal effects originating from the strong plasmonic confinement of light at the nanoscale. The specific design of the nanoparticle arrangement is crucial to optimize the generation of heat and control its flux. Accurate manipulation of the photo-thermal response o...

Metalenses offer the ground-breaking opportunity to realize highly performing low-weight, flat and ultrathin, optical elements which substantially reduce size and complexity of imaging systems. Today, a major challenge in metalenses design is still the realization of achromatic optical elements ideally focussing a broad wavelength spectrum at a sin...

A novel technique is reported to improve the resolution of two-photon direct laser writing lithography. Thanks to the high collimation enabled by extraordinary $\varepsilon_{NZ}$ (near-zero) metamaterial features, ultra-thin dielectric hyper resolute nanostructures are within reach. With respect to the standard direct laser writing approach, a size...

This work reports on numerical and experimental results obtained in plasmonic metal–insulator nanocavities. The systems are composed of silver as metal, and different materials as insulator, namely polyvinylpyrrolidone (PVP), indium tin oxide (ITO), and zinc oxide (ZnO). The proposed nanocavities exhibit extraordinary optical effects as tunable col...

The interplay between quantum emitters and plasmonic nanostructures can unlock unprecedented functionalities, potentially useful for novel‐concept photonics. In this work, the design and conceptual implementation of an integrated photonic‐plasmonic transistor is reported. A mixed top‐down and bottom‐up nanofabrication approach has been used to real...

This work presents numerical and experimental results of plasmonic Metal-Insulator optical nano-cavities. The systems are composed of Silver as metal, polyvinylpyrrolidone or indium tin oxide or zinc oxide as insulator. The proposed nano-cavities exhibit extraordinary effects as colors changing in function of the incident/view angles, enhancement o...

Optical modulators are key ingredients in optoelectronics applications ranging from energy harvesting, sensor and imaging devices. In this framework, nonlinear photon conversion mechanisms constitute an attractive opportunity to add logic capabilities to these apparatuses. Here, we investigate the directionality of the emitted second harmonic signa...

In this paper, we present a simple and robust numerical method able to predict, with high accuracy, the photo-thermal effects occurring for a gold nanoparticles arrangement under externally applied strain. The physical system is numerically implemented in the COMSOL Multiphysics simulation platform. The gold nanoparticles distributions are excited...

In this paper, we present a simple and robust numerical method capable of predicting, with high accuracy, the thermal effects occurring for different gold nanoparticle arrangements under externally applied strain. The physical system is numerically implemented in the COMSOL Multiphysics simulation platform. The photothermal response of different ar...

A simple and robust method able to predict, with high accuracy, the optical properties of single and multi-layer nanostructures is presented. The method exploits a COMSOL Multiphysics simulation platform and it has been validated by three case studies with increasing numerical complexity: i) a single thin layer (20 nm) of Ag deposited on a glass su...

A simple and robust method able to predict, with high accuracy, the optical properties of single and multi-layer nanostructures is presented. The method exploits a COMSOL Multiphysics simulation platform and it has been validated by three case studies with increasing numerical complexity: i) a single thin layer (20 nm) of Ag deposited on a glass su...

We investigate the discrete diffraction phenomenon in a Polymer-Liquid Crystal-Polymer Slices (POLICRYPS) overlaying a random distribution of gold nanoparticles (AuNPs, plasmonic elements). We study the propagation of a CW green laser beam through the waveguide structure as a function of beam polarization, laser intensity and sample temperature. It...

In this contribution, we show how it is possible to rigorously predict strain-related phenomena in case of plasmonic systems made of arrangements of metallic nanoparticles immobilized on a flexible elastomeric tape. This insight allows the study of the thermal response of the system and of the heat photogenerated at the nanoscale. Results evidence...

A simple and robust method able to evaluate and predict, with high accuracy, the optical properties of single and multi-layer nanostructures is presented. The method was implemented using a COMSOL Multiphysics simulation platform and it has been validated by four case studies with increasing numerical complexities: (i) a single thin layer (20 nm) o...

A simple and robust method able to calculate and predict, with high accuracy, the optical properties of single and multi-layer materials by exploiting a Comsol Multiphysics simulation platform is presented. For each considered material, it is possible to extract physical quantities of interest like reflectance, transmittance and Brewster angle, for...

In the intriguing field of active plasmonics, liquid crystals are considered a well-suited materials to be used as an active medium [1]. Recently, dual-frequency nematic liquid crystals (DFNLCs) pave the way for the so-called liquid-crystals plasmonics as a modulators since the material enables the tuning of plasmonic properties and behaves as an a...

Research interest on materials and methods to control the nanoscale response of resonant nanostructures is relevant for the potential application in tunable and reconfigurable devices. Typical approaches promote the interplay between external macroscale stimuli (mechanic, thermal, acoustic, electric, and chemical) and plasmonic systems to achieve n...

In this article, we demonstrate the feasibility of self-positioning nanoemitters onto optical waveguides by visible-light nanoscale photopolymerization. A light-sensitive material containing nanoemitters is photopolymerized at interfaces by using the evanes- cent field of the light propagating in photonic structures. By exploiting this method, it i...

Research interest on materials and methods to control the nanoscale response of resonant nanostructures is relevant for the potential application in tunable and reconfigurable devices. Typical approaches promote the interplay between external macroscale stimuli (mechanic, thermal, acoustic, electric, and chemical) and plasmonic systems to achieve n...

This is the seminar I recently gave about my research on Active Plasmonics that I recently gave at the "Centro Servizi Multisettoriale e Tecnologico (CSMT)" of University of Brescia (Italy) on kind invitation of Prof. Costantino De Angelis. The streaming of the seminar is available online at: https://www.youtube.com/watch?v=RYQkYPQ6GTs

In this work, we studied and analysed a particular variety of liquid crystals, the so-called dual-frequency nematic liquid crystals (DFNLCs). The interest was to perform dielectric spectroscopy and optical characterisation with two pure and doped mixtures of DFNLCs. By means the dielectric spectroscopy we observed a low value of crossover frequency...

We experimentally and theoretically demonstrate a class of narrowband transmissive filters in the terahertz spectrum. Their operation is based on the excitation of guided-mode resonances in thin films of the low-loss cyclo-olefin polymer Zeonor, upon which aluminum stripe and patch arrays are patterned via standard photolithography. The filters are...

We present a review of polymer-liquid crystal-based devices for optical applications. Starting from a particular fabrication technique, which enables to obtain the POLICRYPS (POlymer LIquid CRYstal Polymer Slices) structure, we illustrate different realizations, along with their working principle and main features and performances. The name POLICRY...

My presentation at the Liquid Crystals Conference (CLC2018) held in Jastrzębia Góra (Poland) from 17th to 21st September 2018

Photo-anisotropic properties of a particular command layer for Liquid Crystals (LCs), based on azo-benzene material, are exploited to control the photo-thermal response of a single layer of homogeneously and uniformly distributed Au nanoparticles, immobilised on a glass substrate. Experiments demonstrate that the intrinsic anisotropy of materials c...

The opto-mechanical control of the heat generated by an amorphous arrangement of homogenously distributed gold nanoparticles (AuNPs), excited by an external laser source, is investigated. Application of a macroscopic mechanical strain to the biocompatible elastomeric tape supporting the particles leads to a nanoscale modification of their mutual in...

This is the supplementary information (ESI) for our paper recently published on Nanoscale reporting about Flexible thermo-plasmonics

By structuring a luminescent dielectric interface as a relief diffraction grating with nanoscale features, it is possible to control intensity and direction of emitted light. The composite structure of the grating is based on a fluorescent dye (Lumogen F RED 305) dispersed in a polymeric matrix (polymethylmethacrylate, PMMA). Measurements demonstra...

This presentation reports our result about a novel way to induce localized thermal response by exciting a system of plasmonic units supported by a flexible polymeric substrate (PDMS). A modification of local temperature is produced by applying a strain on the substrate. On this way, the plasmonic units modify their inter-distance and get coupled ge...

This study aims to investigate the potential of small densely packed tilted Au nanorods grown on a flexible substrate by physical vapor deposition for strain sensing. By exciting the rods with linearly polarized white light, perpendicularly impinging onto the sample substrate, interesting plasmonic properties emerge. Electron microscopy characteriz...

The use of biomaterials as optical components has recently attracted attention because of their ease of functionalization and fabrication, along with their potential use when integrated with biological materials. We present here an observation of the optical properties of a silk-azobenzene material (Azosilk) and demonstrate the operation of an Azos...

The spectral response of a terahertz (THz) filter is investigated in detail for different angles of incidence and polarization of the incoming THz wave. The filter is fabricated by patterning an aluminum frequency-selective surface of cross-shaped apertures on a thin foil of the low-loss cyclo-olefin polymer Zeonor. Two different types of resonance...

Policryps structures of photo-curable adhesive NOA61 and nematic liquid crystal mixture E7 have been created inside selected microchannels of photonic crystal fibers (PCF). The PCF was selectively infiltrated with the photopolymer-liquid crystal mixture for the writing of a holographic tunable grating inside specific holes of the photonic fiber. A...

Wire-grid polarizers constitute a traditional component for the control of polarization in free-space devices that operate in a broad part of the electromagnetic spectrum. Here, we present an aluminium-based THz wire grid polarizer, fabricated on a sub-wavelength thin flexible and conformal foil of Zeonor polymer having a thickness of 40µm. The fab...

Gold nanoparticles (GNPs) have proven to be good nano-sources of heat in the presence of specific electromagnetic radiation. This process, in fact, becomes strongly enhanced under plasmon resonance. In particular, the amount of generated heat and the consequent temperature increase depend on the number of GNPs that are collectively excited and on t...

In this contribution, a numerical study of the optical properties of closely-packed gold nanorods was performed. The studied nano-objects are experimentally grown on a tilted polydimethylsiloxane (PDMS) substrate by using physical vapor deposition (PVD). This method creates nanorods tilted to a certain angle with respect to the substrate normal. Th...

We study theoretically and numerically bi-dimensional square gratings of mono\-mers and dimers of gold nanocylinders supported on a dielectric substrate, under plane wave illumination as a function of the angle of incidence and of the polarization. The number of parameters investigated makes that system a rich platform for the investigation of how...

Periodical elements made by stacking thin layers of the cyclo-olefin polymer Zeonor, separated by spacers made of bi-adhesive tape, are used as building blocks for realizing tunable terahertz (THz) filters. The basic block is a Bragg reflector whose bandgap can be controlled by changing the geometrical features of the periodical elements. By combin...

Mechanically tunable Bragg filters at terahertz frequencies are designed, fabricated by a simple procedure, and characterized via THz time-domain spectroscopy. The Bragg reflectors are composed by stacking thin cyclo-olefin Zeonor polymer layers, which are separated by spacers made of a bi-adhesive tape. The defect cavity is void and its thickness...

A THz wire grid polarizer on cyclo-olefin Zeonor polymer film that exhibits high extinction ratio and low losses is theoretically and experimentally investigated. The polarizer has an extinction ratio between 30 and 45 dB and insertion losses below 1 dB in the 0.3–2.5 THz range. The high-performance characteristics of the polarizer are preserved ev...