Microlenses are of technological importance for a wide range of industrial applications enabling in a single element the demand for small form factors, high resolution, and cost effectiveness. The micro-optical elements composed of a series of lens, with diameters ranging from several micrometers to several millimeters have been successfully employed in imaging, sensing, photovoltaics, solar concentrators and optical communications applications. In the last decades, microlenses have been manufactured using multi-step processes such as photolithography, resist-melting, soft-lithography and hot-embossing. More recently, simple and efficient manufacturing methods have emerged in the fabrication of microlenses, which allow the use of different materials and give greater freedom with regards to the choice of substrates and array patterns, like Drop-on-Demand (DoD) inkjet printing. Here we discuss about the dispensing of liquid crystal by pyro-electrohydrodynamic (pyro-EHD) printing. The pyro-electric effect is here used for the non-contact manipulation of liquid solution in air and at room temperature. The results obtained show the great feasibility in the dispensing process in terms of materials, geometry and optical properties.
This conference presentation was prepared for the Plasmonics: Design, Materials, Fabrication, Characterization, and Applications XX conference at SPIE Optics + Photonics 2022.
We aim to realize a novel nanotechnology-based biosensor specifically utilized to detect harmful bacteria in potable water. The nano-inspired device makes use of a chemically functionalized gold nanorods array (for the selective selection of specific pathogens) layered with a photo-responsive nematic liquid crystal (NLC) film for real-time and high sensitivity detection. The first experimental results are presented and discussed.
Thermo-plasmonics deals with the generation of nanoscale heating produced by light activated plasmonic nanoparticles (NPs) such as gold and silver NPs. The combination of smart-responsive materials (e.g. thermotropic liquid crystals and thermo-responsive hydrogels) and highly photo-thermal efficient plasmonic (gold) NPs has been used for the realization of light assisted, reconfigurable, thermo-plasmonic driven Bragg mirrors, diffraction gratings, waveplates and smart windows.
The fourth generation optics (4G optics) enables the realization of novel optical components (lenses, gratings, vector vortices, etc.) by patterning the optical axis orientation in the plane of an anisotropic film. Such components exhibit near 100% diffraction efficiency for wavelengths meeting half-wave retardation condition. In this framework, we have advanced a step-forward by realizing different diffractive waveplates (DWs) with arbitrary spatial patterns of the optical axis orientation by exploiting the capability of a Digital Spatial Light Polarization Converter (DSLPC). The DSLPC is based on a reflective, high resolution Spatial Light Modulator (SLM) combined with an “ad hoc” optical setup. The most attractive feature of the use of a DSLPC for photoalignment is that the orientation of the alignment layer, and therefore of the fabricated liquid crystal (LC) or liquid crystal polymer (LCP) DWs, can be specified on a pixel-by-pixel basis. By varying the optical magnification or de-magnification between the SLM and the alignment layer, the spatial resolution of the photoaligned layer can be adjusted to be optimal for each application. We show that with a simple “click” it is possible to record different high resolution optical components as well as arbitrary patterns ranging from lenses to invisible and even dual labels.
We report on photo-thermal effects observed in gold nanoparticles (GNPs) dispersed in Nematic Liquid Crystals (NLCs). Under a suitable optical radiation, GNPs exhibit a strong light absorption/scattering; the effect depends on the refractive index of the medium surrounding the nanoparticles, which can be electrically or optically tuned. In this way, the system represents an ideal nano-source of heat, remotely controllable by light to adjust the temperature at the nanoscale. Photo-induced temperature variations in GNPs dispersed in NLCs have been investigated by implementing a theoretical model based on the thermal heating equation applied to an anisotropic medium; theoretical predictions have been compared with results of experiments carried out in a NLC medium hosting GNPs. Both theory and experiments represent a step forward to understand the physics of heat production at the nanoscale, with applications that range from photonics to nanomedicine.
We report on the realization and characterization of a polymeric template sculptured in
photosensitive material, on a chemical inert surface. The structure is devoted to micro/nanoconfinement
and stabilization of a wide range of organic and nano-particle components with selfarrangement
properties at the nanoscale [1]. High quality morphology of a polymeric, micropatterned,
array is obtained by combining a, nano-precision level, optical holographic setup and a
multi-step chemico-physical process. The "universal" template represents the basic platform to be
filled with different organic materials, which can also include metallic nano-particles. The long
range self-organization is induced without making use of any kind of surface chemistry. Due to their
capability of exhibiting self organization, light responsive Liquid Crystals (LC) [2] and short pitch
Cholesterics LC [3] have been exploited, and experimental studies have been carried out in order to
investigate the photo-optical and elecro-optical response of obtained composite structures for the
realization of photonic devices. Finally, the possibility of including metallic nano-particles has been
also investigated, with the aim of inducing a "metamaterial" behavior of the realized structure.
We report on the fabrication and characterization of a micro periodic structure realized in soft-composite materials
containing metallic nanoparticles. The particles are used to infiltrate a passive polymer template realized by combining a
holographic curing setup and a microfluidic etching process. In other experiments, small amounts of nanoparticles are
dissolved in the original mixture utilized for the realization of polymer-liquid-crystal-polymer-slices gratings
(POLICRYPS); this enables to fabricate POLICRYPS-like structures showing novel electromagnetic properties.
Obtained structures are characterized in term of impinging probe polarization in the UV/visible range. Correlation
between the optical response and external perturbations (electric field, temperature) is also reported. These first attempts
are oriented to the fabrication of devices with tunable metamaterial properties.
By replacing common buffers with anisotropic liquids in microfluidics, an enhanced range of optofluidic functionalities
is enabled. Such an anisotropic liquid is nematic liquid crystals (NLC), which exhibits optical properties that can be
tuned by optical, electrical or mechanical fields, such as flow. We demonstrate an optofluidic modulator based on direct
flow of nematic liquid crystals in microfluidic channels. We discuss this optofluidic paradigm both under steady state
conditions, and under flow. Rapid pulsatile flows are detrimental towards more compact and ultra-fast devices. These
were enabled via peristaltic pumps, demonstrating liquid crystal modulators operating above the limit of 3 kHz. We
discuss the latter results, but also assess the feasibility of performing ultra-fast optics and additional functionalities for
on- and off-chip imaging.
Surfaces -defined as the interfaces between solids and liquids- have attracted much attention in optics and biology, such
as total internal reflection imaging (TIRF) and DNA microarrays. Within the context of optofluidics however, surfaces
have received little attention. In this paper, we describe how surfaces can define or enhance optofluidic function. More
specifically we discuss chemical interfaces that control the orientation of liquid crystals and the stretching of individual
nucleic acids, diffractive and plasmonic nanostructures for lasing and opto-thermal control, as well as microstructures
that read pressure and form chemical patterns.
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