Surface plasmon resonance detections based on phase changes have demonstrated superior sensitivities over the intensity, spectral and angular methods due to the singularity effect (abrupt change of phase value) observed at resonance. The Goos–Hänchen effect, a higher first order derivative of the phase, can be observable as a lateral displacement of the reflected wave at total internal reflection and magnified by the surface plasmons. The GH sensitivity can be further improved through the addition of a phase change material nanolayer beneath the gold. Vanadium dioxide (VO2) belongs to the family of phase change materials that exhibit reversible insulator-metal behavior when heated above 68℃. Adding a thin layer of VO2 below the metal proved to theoretically enhance the sensitivity of a conventional gold-based surface plasmon biosensor (up to 28 times of improvement in comparison with the bare gold configuration).
In this paper, we have designed and fabricated an atomically thin plasmonic sensing substrate based on two-dimensional phase change material Ge2Sb2Te5 and silver (Ag-GST). This substrate offers an ultra-low reflection in the SPR curves and a strong optical phase singularity. A custom-built SPR setup was developed here to directly measure the phase-singularity-induced lateral position shift. We have obtained a SPR sensitivity regarding the lateral position shift of 9.9577 x 10^7 μm/RIU, which is 3 orders of magnitudes higher than current position shift sensing scheme based on hyperbolic metamaterial. Due to the ultra-high SPR sensitivity, the binding processes between peptide and integrins directly from un-purified liposomes were real-time monitored. The concentrations of Mn2+ ions ranging from 1 fM to 1 mM on the binding dynamics have been systematically monitored with our developed phase-sensitive surface plasmon resonance biosensors.
High-harmonics generation (HHG) in solids require high-energy few-cycle laser drivers at near- to mid-infrared wavelengths with excellent beam quality to reach fluences of ~1 TW/cm2. Along this line, soliton sources based on large mode area silica-core singlemode fibers produce ultrashort (70 fs) pulses at remote wavelengths with hundreds of nJ, thus providing a new platform for driving HHG in solids. In this communication, we explore the potential of such soliton-based fiber driver for HHG in thin-films of zinc oxide. The laser delivers 41 nJ 70 fs solitonic pulses at 1764 nm and drives harmonics generation up to H7.
Vanadium dioxide (VO2) is undergoing a reversible insulator-to-metal transition (MIT), subject to thermal, electrical or optical stimuli. The transition is accompanied by drastic changes in the material’s electrical and optical properties which, along the MIT broadband frequency response (from DC to microwaves, THz/ optical domains), triggered a plethora of interesting applications (DC to millimeter-waves switching, THz modulators, reconfigurable filters and antennas etc.). Here we report on optical switching of the VO2 material between its two dissimilar states when integrated in planar two terminal electrical devices and submitted to laser pulses with different temporal lengths from a high-power laser diode operating at 980 nm. During optical irradiation of VO2 films with pulses having mean powers between 15mW and 140mW at repetition rates up to 500 kHz, we monitored its resistance change, witnessing on the MIT onset. We demonstrate that the MIT in VO2 is optically triggered for pulses as short as 25 ns and energies higher than 130 nJ/pulse, with insulator-to-metal response times in the range 10-15 ns. The process is highly stable and reliable; the devices are able to perform more than one billion switching cycles at frequencies up to 400 kHz without damaging the material nor the device integrity. This optical activation scheme of VO2 emerges as a promising solution for reconfiguration applications at THz and millimeter-waves frequencies.
One of the most peculiar characteristics of the insulator-to-metal transition (MIT) in vanadium dioxide (VO2) material is its broadband response, manifested by drastic electrical and dielectric properties changes between the insulator and metallic states on a very large frequency spectrum. We are presenting the characterization of the MIT in VO2 films over a wide range of the electromagnetic spectrum (75-110GHz, 0.1-1.4THz) and illustrate the materials’ capabilities for manipulating the electromagnetic radiation in the millimeter-waves and THz domains. We demonstrate the possibility of realizing tunable THz devices by introducing this phase transition material as localized patterns in the structure of THz planar metamaterials. We designed, simulated and fabricated tunable VO2-based THz metamaterials devices which show significant variations in their THz transmission under the effect of thermal stimuli but also by applying an electrical voltage across the devices.
We present the vanadium dioxide (VO2) thin films deposition using e-beam evaporation of a vanadium target under oxygen atmosphere on different substrates (sapphire, Si, SiO2/Si…) and we focus on their electrical and optical properties variations as the material undergoes a metal-insulator transition under thermal and electrical stimuli. The phase transition induces extremely abrupt changes in the electronic and optical properties of the material: the electrical resistivity increases up to 5 orders of magnitude while the optical properties (transmission, reflection, refractive index) are drastically modified. We present the integration of these films in simple planar optical devices and we demonstrate electrical-activated optical modulators for visible-infrared signals with high discrimination between the two states. We will highlight a peculiar behavior of the VO2 material in the infrared and far infrared regions (2- 20 μm), namely its anomalous emissivity change under thermal- end electrical activation (negative differential emittance phenomenon) with potential applications in active coatings for thermal regulation, optical limiting or camouflage coatings.
We report on the fabrication of Ti:sapphire channel waveguides. Such channel waveguides are of interest, e.g., as low-threshold tunable lasers. We investigated several structuring methods including ion beam implantation followed by wet chemical etching strip loading by polyimide spin coating and subsequent laser micro-machining, direct laser ablation or reactive ion etching through laser-structured polyimide contact masks. The later two methods result in ribs having different widths and heights up to ~5 μm. By reactive ion etching we have obtained channel waveguides with strong confinement of the Ti:sapphire fluorescence emission.
The preliminary results on the laser synthesis of carbonaceous nanoparticles, which exhibit some characteristic features of fullerene/iron complexes, are reported. The nanopowders were obtained by the laser pyrolysis of a gas phase mixture containing hydrocarbon and alternatively iron pentacarbonyl vapors or ferrocene aerosols. The vapors of iron pentacarbonyl were carried out in the reactor through the intermediate of a bubblier; in the runs using ferrocene, this one was solved in benzene and brought into the reaction zone as aerosol. The reactant mixture contained also nitrous oxide, as oxidizer, and sulphur hexafluoride as energy transfer agent. The as- synthesized powders were toluene extracted and characterized by different analytical methods, such as High Performance Liquid Chromatography (HPLC), IR transmission spectroscopy and Moessbauer spectroscopy. The identification of fullerene-metal complexes was performed by Moessbauer spectroscopy. The Moessbauer transmission spectrum has evidenced the formation of both fullerene phases with iron inside and outside the cage.
Since the theoretical studies of Liu and Cohen who predicted the existence of a superhard phase of carbon nitride, a great deal of effort was underdone in order to synthesize this hypothetical material with a nitrogen content as high as the 57% present in a (beta) -C3N4 structure. This study presents an attempt to produce CNx thin films using the laser-induced CVD technique. CW CO2 laser was used for irradiating various carbon-nitrogen containing mixtures such as C2H4/N2O/NH3. The CNx films were grown alternatively on bare alumina ((alpha) - Al2O3) substrates and on pre-deposited Ti films. A comparative analysis of nitrogen incorporation in the films obtained in different experimental conditions was performed by means of the X-ray photoelectron spectroscopy. The same method was used to identify the chemical states of the CN system.
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