Design of 1D photonic crystals for colorimetric and ratiometric refractive index sensing

Abstract Photonic crystals can be employed effectively as simple and low-cost colorimetric sensors for monitoring variation in the environmental refractive index. In most cases, the photonic colorimetric approach relies on the use of porous and permeable materials to highlight refractive index (RI) modulation, although a fine control over the size distribution and free volume can be complex to achieve. Here, we propose nonporous low-layer count distributed Bragg reflectors (DBRs) as simple optical devices for colorimetric refractive index sensing. In our feasibility study, we simulated the reflectance of DBRs consisting of two to five SiO2/TiO2 bilayers upon variation of the external refractive index. We found that the 2-bilayers sample exhibits the highest sensitivity to RI variations, and identified the ratio between the first and third order reflectance intensity as simple yet efficient ratiometric parameter to discern analytes with different refractive indices. This approach can provide a promising perspective for the development of cheap and portable devices for environmental detection of a wide range of substances

Tamm Plasmon Resonance as Optical Fingerprint of Silver/Bacteria Interaction

Incorporation of responsive elements into photonic crystals is an effective strategy for building up active optical components to be used as sensors, actuators and modulators. In these regards, Tamm Plasmon (TP) modes have arisen recently as powerful optical tools for the manipulation of light-matter interaction and for building sensors/actuators. These emerge at the interface between a dielectric mirror and a plasmonic layer and, interestingly, can be excited at normal incidence angle with relatively high quality factors. Although its field is located at the interface between the dielectric mirror and the metal, recent studies have demonstrated that corrugation at the nanoscale permits to access the TP mode from the outside, opening new exciting perspectives for many real-life applications. Here, we show that the TP resonance obtained by capping a distributed Bragg reflector with a nanostructured layer of silver is sensitive to the presence of bacteria. We observed that nanoscale corrugation is essential for accessing the TP field, while the well-known bio-responsivity of silver nanostructures renders such a localised mode sensible to the presence of Escherichia Coli. Electrodoping experiments confirm the pivotal role of nanostructuration, as well as strengthening our hypothesis that the modifications of the TP mode upon exposure to bacteria are related to the accumulation of negative charge due to the bacterial-driven removal of Ag+ ions from its lattice. Finally, we devised a case study in which we disentangled optically the presence of proliferative and non-proliferative bacteria using the TP resonance as a read-out, thus making these devices as promising simple all-optical probes for bacterial metabolic activity, including their response against drugs and antibiotics

The Impact of Bacteria Exposure on the Plasmonic Response of Silver Nanostructured Surfaces

Silver, especially in the form of nanostructures, is widely employed as an antimicrobial agent in a large range of commercial products. The origin of the biocidal mechanism has been elucidated in the last decades, and most likely originates from silver cation release due to oxidative dissolution followed by cellular uptake of silver ions, a process that causes a severe disruption of bacterial metabolism and eventually leads to eradication. Despite the large number of works dealing with the effects of nanosilver shape/size on the antibacterial mechanism and on the (bio)physical chemistry pathways that drive bacterial eradication, little effort has been devoted to the investigation of the silver NPs plasmon response upon interaction with bacteria. Here we present a detailed investigation of the bacteria-induced changes of the plasmon spectral and dynamical features after exposure to one of the most studied bacterial models, Escherichia Coli. Ultrafast pump-probe measurements indicate that the dramatic changes on particle size/shape and crystallinity, which stem from a bacteria-induced oxidative dissolution process, translate into a clear modification of the plasmon spectral and dynamical features. This study may open innovative new avenues in the field of biophysics of bio-responsive materials, with the aim of providing new and reliable biophysical signatures of the interaction of these materials with complex biological environments

Εtude de cristaux de CaF2 Νd Lu pοur lasers de haute énergie

It was recently demonstrated that efficient and broadband laser emission was possible with Nd-doped CaF2 and SrF2 single crystals around 1.05 µm. Such laser emission, known as completely quenched because of cross-relaxation in the singly doped fluorites, increases spectacularly by co-doping with non-optically active “buffer” ions like Y3+ or Lu3+. Broadband laser emission and ultra-short laser operation are therefore possible. The material is particularly appealing for large scale high peak power diode-pumped amplifiers. A deep investigation of the spectral properties of CaF2:Nd3+ crystals co-doped with various amounts of Lu3+ was performed. The cluster breaking effect of Lu3+ codoping has as a side-effect the appearance of two different contributions, identified as two different active sites, which is in agreement with recent observations. In this work, we investigate in depth the different centres’ spectroscopic properties and operational parameters for laser applications,their evolution as the lutetium concentration increases, and the thermomechanical properties of said samples. A preliminary investigation on the amplification properties and laser operation of said materials is performed as well.La possibilité d’obtenir une émission laser efficace sur une large bande spectrale autour de 1.05 µm a été démontrée récemment en utilisant des monocristaux CaF2 and SrF2 dopés Nd3+. Cette émission, éteinte du fait de la relaxation croisée entre ions dans les matériaux de type fluorite, peut être exaltée avec l’insertion d’ions “tampons” comme Y3+ ou Lu3+. Une émission laser accordable sur une large bande spectrale et la génération d’impulsions ultracourtes sont donc possibles. De plus, ce type de matériau est particulièrement intéressant pour des amplificateurs de forte puissance pompés par diodes. Une étude complète des propriétés spectrales et thermomécaniques de cristaux de CaF2:Nd3+ co-dopés avec des concentrations variables de Lu3+ a été menée en collaboration avec le CEA CESTA au sein du projet LASCAN pour de futurs développements au sein du Laser MégaJoule (LMJ) avec pour but l’amélioration des performances des amplificateurs pilotes. L’effet d’élimination des clusters de Nd3+ par le co-dopage avec le Lu3+ et l’apparition de deux sites actifs différents a été mise en évidence et caractérisée en détail. Ce travail présente ainsi une spectroscopie complète des centres actifs dans CaF2:Nd3+,Lu3+, une étude des propriétés thermomécaniques, ainsi que des propriétés d’amplification optique des matériaux étudiés

Bringing the interaction of silver nanoparticles with bacteria to light

In the last decades the exploitation of silver nanoparticles in novel antibacterial and detection devices have risen to prominence for their well-known specific interaction with bacteria. The vast majority of studies focus on the investigation over the mechanism of action underpinning bacterial eradication, while little efforts have been devoted to the modification of silver optical properties upon interaction with bacteria. Specifically, given the characteristic localized surface plasmon resonance of silver nanostructures, which is sensitive to changes in the charge carrier density or in the dielectric environment, these systems can offer a handle in the detection of bacteria pathogens. In this review, we present the state of art of the research activity on the interaction of silver nanoparticles with bacteria, with emphasis on the modification of their optical properties. This may indeed lead to easy color reading of bacterial tests and pave the way to the development of nanotechnology silver based bacterial detection.Comment: This article has been submitted to the journal Biophysics Review

The Impact of Tamm Plasmons on Photonic Crystals Technology

This review describes hybrid photonic-plasmonic structures based on periodic structures that have metallic coatings or inserts which make use of the Tamm plasmon for sensing applications. The term Tamm plasmon refers a particular resonance resulting from the enhancement of a surface plasmon resonance absorption via coupling to a wavelength-matching photonic bandgap provided by a photonic crystal. Tamm plasmon-based devices come in an ample variety of material and geometric combinations, each designed to perform a specific kind of measurement. While the physical effect is quite well documented and understood, its implementation in devices is still a rapidly developing and thriving field, which leaves open many possibilities for novel designs and new applications. We therefore aim of giving a complete overview on the topic, so as to provide an ordered collection of designs and uses, as well as to spur further development on the subject of the Tamm plasmon for sensing applications

Mid-infrared laser operation of Er3+ -doped BaF2 and (Sr,Ba)F2 crystals

We report on the first, to our knowledge, mid-infrared laser operation of two Er 3+ -doped barium-containing fluorite-type crystals, BaF 2 and (Sr,Ba)F 2 , featuring a low-phonon energy behavior. A continuous wave 4.9 at.% Er:(Sr,Ba)F 2 laser generated 519 mW at 2.79 µm with a slope efficiency of 25.0% and a laser threshold of 27 mW. The vibronic and spectroscopic properties of these crystals are determined. The phonon energy of (Sr,Ba)F 2 is as low as 267 cm −1 . The Er 3+ ions in this crystal feature a broadband emission owing to the 4 I 11/2 → 4 I 13/2 transition and a long luminescence lifetime of the 4 I 11/2 level (10.6 ms) making this compound promising for low-threshold, broadly tunable, and pulsed 2.8-µm lasers

Design of a multimode interferometer-based mid-infrared multispecies gas sensor

International audienceA 1 x 2 multimode interferometer beam splitter based on mid-infrared emitting chalcogenides waveguides is designed. This device multiplexes mid-infrared light in two channels whose respective passbands overlap either CO 2 or CO absorption bands, respectively between 4.20-4.32 μm and 4.50-4.86 μm. The proposed device offers a low-cost solution for monolithic combination of broadband on-chip mid-infrared light emission with dispersive spectroscopic element devoted to mid-IR multigas sensing applications. Based on restrictive interference mechanism in a 1 x 2 multimode interferometer, the multimode section dimensions (width and length) are engineered to increase the imbalance between the two ports for the two passbands and consequently to increase the output contrast ratio. Tolerances to variations from the optimum device design resulting from processing conditions (materials fabrication and sputtering, photolithography and dry etching steps) are assessed. In particular, the 1 x 2 multimode interferometer diplexer spectral transmission is investigated as a function of deposited film refractive index and multimode section dimensions (width and length) deviation from designed values. Input and output ports tapering is introduced to reduce the device insertion loss

Radio-frequency sputtering fabrication of chalcogenide-based Er3+-doped vertical optical cavities for near-infrared operation

International audienceChalcogenide-oxide Bragg reflectors and a 1-D vertical cavity for operation at 1.55 gm were designed and fabricated via radio-frequency sputtering. The Bragg reflectors were made out of repeating layers of Al2O3 and As2Se3, and the cavity was obtained via a Ga5Ge20Sb10S65:Er3+ defect layer. The layers' properties were assessed via ellipsometry and SEM imaging. Transmission spectroscopy verifies the appearance of a well-defined stop-band centered around 1.51 mu m with a very wide bandgap, and extremely low transmission, even with a relatively low layer count. The vertical optical cavity fabrication results in the appearance of a resonance within the band, at a wavelength corresponding to the I-4(13/2)-> I-4(15/2) transition of erbium. The high transmittance at 808 and 980 nm allows for optical pumping, and thus light amplification and coherent light generation from the cavity. The operation of these devices was investigated, showing coherent light emission at 1.5 mu m. The results are encouraging in assessing the viability of this design and these materials for operation in the near-infrared range, providing an important step towards the fabrication of chalcogenide-based optical amplifiers for the near-infrared

Er:LiYF4 planar waveguide laser at 2.8 μm

International audienceWe report on a mid-infrared Erbium planar waveguide laser operating on the 4 I 11/2 → 4 I 13/2 transition. It employs a heavily-doped 10.6 at.% Er 3+ :LiYF 4 single-crystalline layer grown by Liquid-Phase Epitaxy (LPE). The waveguide laser delivers a maximum output power of 191 mW at ~2809 nm with a slope efficiency of 15%, a linear polarization and a laser threshold of 134 mW. The waveguide propagation losses are 0.4±0.2 dB/cm. The polarized spectroscopic properties of Er 3+ :LiYF 4 layers are also investigated. The stimulated-emission cross-section of Er 3+ ions amounts to 0.87×10 -20 cm 2 at 2809 nm for π-polarization. Er 3+ :LiYF 4 epitaxial layers represent a promising platform for integrated low-loss mid-infrared light sources