In a recently published article in ACS Nano, we demonstrate a SERS substrate capable of reproducible measurements, such that the relative concentration of a mixture of SERS active molecules can be determined. Surface enhanced Raman spectroscopy has become a widely used research tool for the identification of molecules, but has yet to achieve widespread use outside of academia. The dominant method for generating the required spectra is to use colloidal metallic nanoparticles, but this leads to an inherently random distribution of SERS-active sites, and thus although the signal can uniquely identify a molecule, the intensity of that signal will vary, rendering quantitative analysis impossible. We use… Read More »Reproducible SERS Substrate
In a work published recently in Optics Express we experimentally investigated the occurrence of optical dispersive shock waves (DSWs) in silica aerogel (SA). Here we studied the interplay between disorder and nonlinearity; on the other hand the determination of the conditions for the suppressions of the DSWs, is fundamental for the realization of high power nonlinear optical devices based on SA. The convection-free solid-state structure of SA gives peculiar thermal properties, such as very low heat conductivity and high melting point, making this material robust with respect to very high nonlinear regimes, a topic so far unexplored. This is at variance with most the systems presenting thermal nonlinearity, that being dyed soft-matter, exhibit boiling… Read More »Optical Shock Waves in Silica Aerogel
In a recent paper published in Optics Letter we demonstrate that a random medium can be used as a cheap and reliable wavemeter. The system is made of a small drop of alumina particles in water solution casted on a glass slide, placed at the end of a fiber coupler as in figure. When propagating through the drop, light of different wavelengths produce specific speckle patterns that can be stored for future reference. The unknown wavelength of a further beam can then be assessed using principal component analysis with a resolution up to 13 pm.
In a paper published in Nature Scientific Report we show how to couple light to subwavelenght plasmonic features using the principle of optical eigenmodes. This technique can be used also in presence of large optical aberrations and allow to selectively couple light to nanofeatures in a crowded region, with minimal crosstalk. In the picture we show a SEM picture of a typical sample (gold nanoantennas on glass) that we fabricated to test the technique.
The Luneburg lens is a gradient index lens that focuses light from all incident directions, thus being free from aberrations that affect conventional lenses. Like the Maxwell fish-eye lens or the Eaton lens, the Luneburg lens can be described via non-Euclidean transformation, where light in a medium is experiencing a curved spatial geometry. The Luneburg lens focuses light on the edge of the lens in the same direction of the incident light. The position of the focus thus indicates the direction of light corresponding to a Fourier transform in terms of light waves. Luneburg lenses are commonly used in microwave technology and have recently been… Read More »Transformation Optics in Silicon Photonics
Metamaterials (MMs) are man made materials with unusual electromagnetic properties that are not typically found in Nature. They are the key to achieving such extraordinary properties as invisibility cloaks and perfect lenses. At present, they are bulky and confined to laboratories. If they were flexible, they could become much more versatile and practical. We are working towards a novel concept for flexible MMs (Metaflex) that will turn current cloaking devices from suits of armour into true cloaks. In the following figure a single layer of Metaflex is placed on a commercial disposable contact lens, to show the potential of the approach. Our interest in Metaflex… Read More »Flexible Metamaterials
In Slotted Photonic Crystal (SPhCs) devices the light is squeezed, confined and guided through air cuts realized in a Photonic Crystal (PhC) background. This confining mechanism is based on both the total internal reflection (experienced by the field at the discontinuous edges of the slot) and the resonant confinement offered by the periodicity of the Photonic Crystal. Figure 1 shows the SEM picture of a typical slotted PhC waveguide. In this structures light is confined in extremely reduced volumes, hence with a significant intensity. The narrow air features can then be infiltrated with media spanning from gas to biological analytes to nonlinear and/or active material to take… Read More »Slotted Photonic Crystals