arXiv subjects

Olivier Deparis

Publications and source records attributed to Olivier Deparis.

13 recordsLinked to original sources

arXiv2026

A Mid-Infrared Absorber Inspired by the Wing-Scale Photonic Structure of Troides magellanus

Growing environmental and energy-related challenges have intensified the search for technologies capable of improving energy recovery and resource efficiency. Bioinspired photonic structures offer promising opportunities for the development of efficient infrared absorbers by exploiting optical mechanisms found in natural systems. In this work, we present a bioinspired approach for the design and optimization of a broadband mid-infrared absorber based on the highly absorbing wing scales of the Troides magellanus Magellan birdwing butterfly. The characteristic geometry of the biological structure is rescaled and adapted to shift its optical response from the visible to the infrared spectral range. Numerical simulations are used to investigate the influence of the main geometrical parameters on the spectral absorptance and to identify an optimized configuration. The optimized structure achieves an absorption enhancement of 391% compared with a flat steel reference. The improved optical response is attributed to the optimized high-aspect-ratio geometry, which enhances multiple scattering and light trapping, thereby increasing the effective light-matter interaction area. These results demonstrate the potential of bioinspired geometric scaling as an effective strategy for engineering efficient infrared absorbers and tailoring their spectral response for thermal radiation management and infrared photonic applications.

physics.optics↗

arXiv2021

Naturally occurring fluorescence in transparent insect wings

In spite of the crucial role it is believed to play in nature, fluorescence in natural organisms remains under-investigated from optical, chemical and biological perspectives. One example is the transparent wings of insects from the order Hemiptera: fluorescence emission has so far not been reported in any of the 3,000 described species of the superfamily Cicadoidea. The phenomenon has however been investigated in several butterfly and moth species, in which the coloured wing scales are known to embed fluorophores such as papiliochrome II. Photonic structures present in these scales may mediate the associated light emission. Fluorescence has also been described in the vein joints and the membrane of the transparent wings of damselflies and dragonflies. This emission was attributed to the presence of autofluorescent proteins such as resilin that gives rise to low stiffness and high strain in the biological tissues, allowing passive wing deformations. In this article, we characterised the fluorescence emission from the transparent wings of the grey cicada \textit{Cicada orni} (Linnaeus, 1758) and the common cicada \textit{Lyristes (Tibicen) plebejus} (Scopoli, 1763), using linear and nonlinear optical methods. We compared their properties with the fluorescence emission from two other insects exhibiting transparent wings, namely, \textit{Hemaris fuciformis} (Linnaeus, 1758) commonly known as the broad-bordered bee hawk-moth and the Bornean damselfly \textit{Vestalis amabilis} Lieftinck, 1965. These fluorescent behaviours were optically characterised by one- and multi-photon microscopy and spectrometry, allowing us to infer the symmetry of the material as well as the biological role of the fluorophores in the visual perception of insects and to explain the high absorption by the material in the range 300-400~nm.

physics.bio-ph↗

arXiv2021

Genetic-algorithm-aided ultra-broadband perfect absorbers using plasmonic metamaterials

Complete absorption of electromagnetic waves is paramount in today's applications, ranging from photovoltaics to cross-talk prevention into sensitive devices. In this context, we use a genetic algorithm (GA) strategy to optimize absorption properties of periodic arrays of truncated square-based pyramids made of alternating stacks of metal/dielectric layers. We target ultra-broadband quasi-perfect absorption of normally incident electromagnetic radiations in the visible and near-infrared ranges (wavelength comprised between 420 and 1600 nm). We compare the results one can obtain by considering one, two or three stacks of either Ni, Ti, Al, Cr, Ag, Cu, Au or W for the metal, and poly(methyl methacrylate) (PMMA) for the dielectric. More than 10^17 configurations of geometrical parameters are explored and reduced to a few optimal ones. This extensive study shows that Ni/PMMA, Ti/PMMA, Cr/PMMA and W/PMMA provide high-quality solutions with an integrated absorptance higher than 99% over the considered wavelength range, when considering realistic implementation of these ultra-broadband perfect electromagnetic absorbers. Robustness of optimal solutions with respect to geometrical parameters is investigated and local absorption maps are provided. Moreover, we confirm that these optimal solutions maintain quasi-perfect broadband absorption properties over a broad angular range when changing the inclination of the incident radiation. The study also reveals that noble metals (Au, Ag, Cu) do not provide the highest performance for the present application.

physics.optics↗

arXiv2018

Non-linear optical spectroscopy and two-photon excited fluorescence spectroscopy reveal the excited states of fluorophores embedded in beetle's elytra

Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as non-linear optical techniques offer unique possibilities to investigate the effects of the local environment on the excited states of fluorophores. Herein these techniques are applied for the first time to the study of insects' natural fluorescence. The case of the male Hoplia coerulea beetle is investigated because the scales covering the beetle's elytra are known to possess an internal photonic structure with embedded fluorophores, which controls both the beetle's colouration and the fluorescence emission. An intense two-photon excitation fluorescence signal is observed, the intensity of which changes upon contact with water. A Third-Harmonic Generation signal is also detected, the intensity of which depends on the light polarisation state. The analysis of these non-linear optical and fluorescent responses unveils the multi-excited states character of the fluorophore molecules embedded in the beetle's elytra. The anisotropy of the photonic structure, which causes additional tailoring of the beetle's optical responses, is confirmed by circularly polarised light and non-linear optical measurements.

physics.optics↗

arXiv2015

Quantum vacuum photon modes and repulsive Lifshitz-van der Waals interactions

The bridge between quantum vacuum photon modes and properties of patterned surfaces is currently being established on solid theoretical grounds. Based on these foundations, the manipulation of quantum vacuum photon modes in a nanostructured cavity is theoretically shown to be able to turn the Lifshitz-van der Waals forces from attractive to repulsive regime. Since this concept relies on surface nanopatterning instead of chemical composition changes, it drastically relaxes the usual conditions for achieving repulsive Lifshitz-van der Waals forces. As a case study, the potential interaction energy between a nanopatterned polyethylene slab and a flat polyethylene slab with water as intervening medium is calculated. Extremely small corrugations heights (less than ten nanometers) are shown to be able to turn the Lifshitz-van der Waals force from attractive to repulsive, the interaction strength being controlled by the corrugation height. This new approach could lead to various applications in surface science.

cond-mat.mes-hall↗

arXiv2015

Quantum vacuum photon-modes and superhydrophobicity

Nanostructures are commonly used for developing superhydrophobic surfaces. However, available wetting theoretical models ignore the effect of vacuum photon-modes alteration on van der Waals forces and thus on hydrophobicity. Using first-principle calculations, we show that superhydrophibicity of nanostructured surfaces is dramatically enhanced by vacuum photon-modes tuning. As a case study, wetting contact angles of a water droplet above a polyethylene nanostructured surface are obtained from the interaction potential energy calculated as function of the droplet-surface separation distance. This new approach could pave the way for the design of novel superhydrophobic coatings.

cond-mat.mes-hall↗

arXiv2014

Do CVD grown graphene films have antibacterial activity on metallic substrates?

Accurate assessment of the antibacterial activity of graphene requires consideration of both the graphene fabrication method and, for supported films, the properties of the substrate. Large-area graphene films produced by chemical vapor deposition were grown directly on copper substrates or transferred on a gold substrate and their effect on the viability and proliferation of the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli were assessed. The viability and the proliferation of both bacterial species were not affected when they were grown on a graphene film entirely covering the gold substrate, indicating that conductivity plays no role on bacterial viability and graphene has no antibacterial activity against S. aureus and E. coli. On the other hand, antibacterial activity was observed when graphene coated the copper substrates, resulting from the release of bactericidal cupric ions in inverse proportion to the graphene surface coverage.

physics.bio-ph↗

arXiv2014

A two-in-one superhydrophobic and anti-reflective nanodevice in the grey cicada $\textit{Cicada orni}$ (Hemiptera)

Two separated levels of functionality are identified in the nanostructure which covers the wings of the grey cicada $\textit{Cicada orni}$ (Hemiptera). The upper level is responsible for superhydrophobic character of the wing while the lower level enhances its anti-reflective behavior. Extensive wetting experiments with various chemical species and optical measurements were performed in order to assess the bi-functionality. Scanning electron microscopy imaging was used to identify the nanostructure morphology. Numerical optical simulations and analytical wetting models were used to prove the roles of both levels of the nanostructure. In addition, the complex refractive index of the chitinous material of the wing was determined from measurements.

physics.bio-ph↗

arXiv2014

Plasmon hybridization in pyramidal metamaterials: a route towards ultra-broadband absorption

Pyramidal metamaterials are currently developed for ultra-broadband absorbers. They consist of periodic arrays of alternating metal/dielectric layers forming truncated square-based pyramids. The metallic layers of increasing lengths play the role of vertically and, to a less extent, laterally coupled plasmonic resonators. Based on detailed numerical simulations, we demonstrate that plasmon hybridization between such resonators helps in achieving ultra-broadband absorption. The dipolar modes of individual resonators are shown to be prominent in the electromagnetic coupling mechanism. Lateral coupling between adjacent pyramids and vertical coupling between alternating layers are proven to be key parameters for tuning of plasmon hybridization. Following optimization, the operational bandwidth of Au/Ge pyramids, i.e. the bandwidth within which absorption is higher than 90%, extends over a 0.2-5.8 micrometers wavelength range, i.e. from UV-visible to mid-infrared, and total absorption (integrated over the operational bandwidth) amounts to 98.0%. The omni-directional and polarization-independent high-absorption properties of the device are verified. Moreover, we show that the choice of the dielectric layer material (Si versus Ge) is not critical for achieving ultra-broadband characteristics, which confers versatility for both design and fabrication. Realistic fabrication scenarios are briefly discussed. This plasmon hybridization route could be useful in developing photothermal devices, thermal emitters or shielding devices that dissimulate objects from near infrared detectors.

physics.optics↗

arXiv2013

The fundamental problem of treating light incoherence in photovoltaics and its practical consequences

The incoherence of sunlight has long been suspected to have an impact on solar cell energy conversion efficiency, although the extent of this is unclear. Existing computational methods used to optimize solar cell efficiency under incoherent light are based on multiple time-consuming runs and statistical averaging. These indirect methods show limitations related to the complexity of the solar cell structure. As a consequence, complex corrugated cells, which exploit light trapping for enhancing the efficiency, have not yet been accessible for optimization under incoherent light. To overcome this bottleneck, we developed an original direct method which has the key advantage that the treatment of incoherence can be totally decoupled from the complexity of the cell. As an illustration, surface corrugated GaAs and c-Si thin-films are considered. The spectrally integrated absorption in these devices is found to depend strongly on the degree of light coherence and, accordingly, the maximum achievable photocurrent can be higher under incoherent light than under coherent light. These results show the importance of taking into account sunlight incoherence in solar cell optimization and point out the ability of our direct method in dealing with complex solar cells structures.

physics.optics↗

arXiv2013

Nanoarchitecture in the black wings of Troides magellanus: a natural case of absorption enhancement in photonic materials

The birdwings butterfly Troides magellanus possesses interesting properties for light and thermal radiation management. The black wings of the male exhibit strong (98%) absorption of visible light as well as two strong absorption peaks in the infrared both due to chitin. These peaks are located in the spectral region where the black body emits at 313K. The study of absorption enhancement in this butterfly could be helpful to design highly absorbent biomimetic materials. Observations of the wings using a scanning electron microscope (SEM) reveal that the scales covering the wings are deeply nanostructured. A periodic three-dimensional (3D) model of the scale nanoarchitecture is elaborated and used for numerical transfer-matrix simulations of the absorption spectrum. The complex refractive index of the wing material is approximated by a multi-oscillator Lorentz model, leading to a broad absorption in the visible range as well as two peaks in the infrared. The absorption peak intensities turn out to be dependent on the complexity of the nanostructures. This result clearly demonstrates a structural effect on the absorption. Finally, a comparison with a planar layer of identical refractive index and material volume lead us to conclude that the absorption is enhanced by nanostructures.

physics.optics↗

arXiv2013

First-principle calculation of solar cell efficiency under incoherent illumination

Because of the temporal incoherence of sunlight, solar cells efficiency should depend on the degree of coherence of the incident light. However, numerical computation methods, which are used to optimize these devices, fundamentally consider fully coherent light. Hereafter, we show that the incoherent efficiency of solar cells can be easily analytically calculated. The incoherent efficiency is simply derived from the coherent one thanks to a convolution product with a function characterizing the incoherent light. Our approach is neither heuristic nor empiric but is deduced from first-principle, i.e. Maxwell's equations. Usually, in order to reproduce the incoherent behavior, statistical methods requiring a high number of numerical simulations are used. With our method, such approaches are not required. Our results are compared with those from previous works and good agreement is found.

physics.optics↗

arXiv2012

Influence of the pattern shape on the photonic efficiency of front-side periodically patterned ultrathin crystalline silicon solar cells

Patterning the front side of an ultra-thin crystalline silicon (c Si) solar cell helps keeping the energy conversion efficiency high by compensating for the light absorption losses. A super-Gaussian mathematical expression was used in order to encompass a large variety of nanopattern shapes and to study their influence on the photonic performance. We prove that the enhancement in the maximum achievable photo-current is due to both impedance matching condition at short wavelengths and to the wave nature of light at longer wavelengths. We show that the optimal mathematical shape and parameters of the pattern depend on the c Si thickness. An optimal shape comes with a broad optimal parameter zone where fabricating errors would have much less influence on the efficiency. We prove that cylinders are not the best suited shape. To compare our model with a real slab, we fabricated a nanopatterned c Si slab via Nano Imprint Lithography.

physics.optics↗