Publications
129 results found
Ta VD, Caixeiro S, Saxena D, et al., 2021, Biocompatible Polymer and Protein Microspheres with Inverse Photonic Glass Structure for Random Micro‐Biolasers, Advanced Photonics Research, Vol: 2, ISSN: 2699-9293
Ta VD, Caixeiro S, Saxena D, et al., 2021, Biocompatible polymer and protein microspheres with inverse photonic glass structure for random micro‐biolasers, Advanced Photonics Research, Vol: 2, Pages: 1-7, ISSN: 2699-9293
The miniaturization of random lasers to the micrometer scale is challenging but fundamental for the integration of lasers with photonic integrated circuits and biological tissues. Herein, it is demonstrated that random lasers with a diameter from 30 to 160 μm can be achieved by using a simple emulsion process and selective chemical etching. These tiny random laser sources are made of either dye-doped polyvinyl alcohol (PVA) or bovine serum albumin (BSA) and they are in the form of microporous spheres with monodisperse pores of 1.28 μm in diameter. Clear lasing action is observed when the microporous spheres are optically excited with powers larger than the lasing threshold, which is 154 μJ mm−2 for a 75 μm diameter PVA microporous sphere. The lasing wavelength redshifts 10 nm when the PVA microsphere diameter increases from 34 to 160 μm. For BSA microspheres, the lasing threshold is around 55 μJ mm−2 for a 70 μm diameter sphere and 104 μJ mm−2 for a 35 μm diameter sphere. The simple fabrication process reported allows for detail studies of morphology and size, important for fundamental studies of light–matter interaction in complex media, and applications in photonic integrated circuits, photonic barcoding, and optical biosensing.
Tirole R, Attavar T, Dranczewski J, et al., 2021, Time Diffraction in an Epsilon-Near-Zero Metasurface
We observe strong, efficient all-optical modulations and frequency-shift due to time diffraction in a thin film of ITO over gold. Excitation of the Berreman mode leads to redshift and spectral broadening from a nonlinear grating.
Sortino L, Zotev PG, Sapienza R, et al., 2021, Enhanced light-matter interaction in atomically thin semiconductors and 2D single photon emitters coupled to dielectric nano-antennas
Florescu M, Tavakoli N, Spalding RJ, et al., 2021, Hyperuniform and Local Self-Uniform Solar Light Absorbers
We explore the ability of hyperuniform disordered structures to improve light absorption in thin-film architectures. We show that hyperuniform and local selfuniform structuring has a major impact on the radiation absorption processes and that hyperuniform and local selfuniform correlations may be designed to enhance the coupling to quasi-guided modes supported by the thin film and minimize the energy in the radiative channels. We present a through comparison with fully optimized periodic and quasiperiodic structures accounting for both the structuring of the anti-reflective layer refractive index and the back reflector. We show that not only the correlations of present in the disordered structures but also the statistical isotropy and homogeneity of the hyperuniform and local self-uniform materials has a significant impact on the device performance. We report a theoretical solar energy absorption of 84% in a broad bad spectral range 400-1050 nm, in a one micron-thick Si membrane, which is, to the best of our knowledge, the best value achieved in ultra-thin Si membranes and preliminary experimental results.
Granchi N, Spalding R, Lodde M, et al., 2021, Near-field optical investigation of Hyperuniform Disordered photonic structures, Pages: 1013-1014
Located in-between random structures and perfectly ordered photonic crystals, there is a special class of disordered heterostructures called hyperuniform disordered (HuD) photonic structures. These materials, due to the presence of a photonic bandgap, combine the advantages of disordered systems and ordered systems: here, we underline and experimentally prove all these advantages by means of the first near-field optical characterization of HuD photonic structures in the near IR.
Bruno V, Devault C, Vezzoli S, et al., 2021, Negative refraction in time-varying, strongly-coupled plasmonic antenna-ENZ systems, Pages: 989-990
We demonstrate high efficiency in the generation of optical induced time-reversal phase conjugate and negative refraction waves, from a temporal modulated deeply subwavelength epsilon-near-zero (ENZ) film integrated within a plasmonic metasurface. The strong coupling between the plasmonic resonance and the ENZ modes leads to a conversion efficiency that is more than 4 orders of magnitude greater than the bare ENZ film.
Sortino L, Zotev PG, Sapienza R, et al., 2021, Enhanced light-matter interaction in atomically thin semiconductors and 2D single photon emitters coupled to dielectric nano-antennas
Tirole R, Attavar T, Dranczewski J, et al., 2021, Time Diffraction in an Epsilon-Near-Zero Metasurface, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
Sortino L, Zotev PG, Sapienza R, et al., 2021, Enhanced light-matter interaction in atomically thin semiconductors and 2D single photon emitters coupled to dielectric nano-antennas, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Lee JB, Walker H, Li Y, et al., 2020, Template dissolution interfacial patterning of single colloids for nanoelectrochemistry and nanosensing, ACS Nano, Vol: 14, Pages: 17693-17703, ISSN: 1936-0851
Deterministic positioning and assembly of colloidal nanoparticles (NPs) onto substrates is a core requirement and a promising alternative to top-down lithography to create functional nanostructures and nanodevices with intriguing optical, electrical, and catalytic features. Capillary-assisted particle assembly (CAPA) has emerged as an attractive technique to this end, as it allows controlled and selective assembly of a wide variety of NPs onto predefined topographical templates using capillary forces. One critical issue with CAPA, however, lies in its final printing step, where high printing yields are possible only with the use of an adhesive polymer film. To address this problem, we have developed a template dissolution interfacial patterning (TDIP) technique to assemble and print single colloidal AuNP arrays onto various dielectric and conductive substrates in the absence of any adhesion layer, with printing yields higher than 98%. The TDIP approach grants direct access to the interface between the AuNP and the target surface, enabling the use of colloidal AuNPs as building blocks for practical applications. The versatile applicability of TDIP is demonstrated by the creation of direct electrical junctions for electro- and photoelectrochemistry and nanoparticle-on-mirror geometries for single-particle molecular sensing.
Rubino A, Huq T, Dranczewski J, et al., 2020, Efficient third harmonic generation from FAPbBr(3) perovskite nanocrystals, Journal of Materials Chemistry C, Vol: 8, Pages: 15990-15995, ISSN: 2050-7526
The development of versatile nanostructured materials with enhanced nonlinear optical properties is relevant for integrated and energy efficient photonics. In this work, we report third harmonic generation from organic lead halide perovskite nanocrystals, and more specifically from formamidinium lead bromide nanocrystals, ncFAPbBr3, dispersed in an optically transparent silica film. Efficient third order conversion is attained for excitation in a wide spectral range in the near infrared (1425 nm to 1650 nm). The maximum absolute value of the modulus of the third order nonlinear susceptibility of ncFAPbBr3, χ(3)NC, is derived from modelling both the linear and nonlinear behaviour of the film and is found to be χ(3)NC = 1.46 × 10−19 m2 V−2 (or 1.04 × 10−11 esu) at 1560 nm excitation wavelength, which is of the same order as the highest previously reported for purely inorganic lead halide perovskite nanocrystals (3.78 × 10−11 esu for ncCsPbBr3). Comparison with the experimentally determined optical constants demonstrates that maximum nonlinear conversion is attained at the excitonic resonance of the perovskite nanocrystals where the electron density of states is largest. The ease of synthesis, the robustness and the stability provided by the matrix make this material platform attractive for integrated nonlinear devices.
Persano L, Szukalski A, Gaio M, et al., 2020, Dye stabilization and wavelength tunability in lasing fibers based on DNA, Advanced Optical Materials, Vol: 8, ISSN: 2195-1071
Lasers based on biological materials are attracting an increasing interest in view of their use in integrated and transient photonics. Deoxyribonucleic acid (DNA) as optical biopolymer in combination with highly emissive dyes has been reported to have excellent potential in this respect. However, achieving miniaturized lasing systems based on solid-state DNA shaped in different geometries to confine and enhance emission is still a challenge, and the physicochemical mechanisms originating fluorescence enhancement are not fully understood. Herein, a class of wavelength-tunable lasers based on DNA nanofibers is demonstrated, for which optical properties are highly controlled through the system morphology. A synergistic effect is highlighted at the basis of lasing action. Through a quantum chemical investigation, it is shown that the interaction of DNA with the encapsulated dye leads to hindered twisting and suppressed channels for the nonradiative decay. This is combined with effective waveguiding, optical gain, and tailored mode confinement to promote morphologically controlled lasing in DNA-based nanofibers. The results establish design rules for the development of bright and tunable nanolasers and optical networks based on DNA nanostructures.
Sapienza R, Morozov S, Vezzoli S, et al., 2020, Electrical control of single-photon emission in highly-charged individual colloidal quantum dots, Science Advances, Vol: 6, ISSN: 2375-2548
Electron transfer to an individual quantum dot promotes the formation of charged excitons with enhanced recombination pathways and reduced lifetimes. Excitons with only one or two extra charges have been observed and exploited for very efficient lasing or single–quantum dot light-emitting diodes. Here, by room-temperature time-resolved experiments on individual giant-shell CdSe/CdS quantum dots, we show the electrochemical formation of highly charged excitons containing more than 12 electrons and 1 hole. We report the control over intensity blinking, along with a deterministic manipulation of quantum dot photodynamics, with an observed 210-fold increase in the decay rate, accompanied by 12-fold decrease in the emission intensity, while preserving single-photon emission characteristics. These results pave the way for deterministic control over the charge state, and room-temperature decay rate engineering for colloidal quantum dot–based classical and quantum communication technologies.
Kalinic B, Cesca T, Mignuzzi S, et al., 2020, All-dielectric silicon nanoslots for Er3+ photoluminescence enhancement, Physical Review Applied, Vol: 14, Pages: 014086 – 1-014086 – 11, ISSN: 2331-7019
We study, both experimentally and theoretically, the modification of Er3+ photoluminescence properties in Si dielectric nanoslots. The ultrathin nanoslot (down to 5-nm thickness), filled with Er in SiO2, boosts the electric and magnetic local density of states via coherent near-field interaction. We report an experimental 20-fold enhancement of the radiative decay rate with negligible losses. Moreover, via modifying the geometry of the all-dielectric nanoslot, the outcoupling of the emitted radiation to the far field can be strongly improved, without affecting the strong decay-rate enhancement given by the nanoslot structure. Indeed, for a periodic square array of slotted nanopillars an almost one-order-of-magnitude-higher Er3+ PL intensity is measured with respect to the unpatterned structures. This has a direct impact on the design of more efficient CMOS-compatible light sources operating at telecom wavelengths.
Collins H, Barnes B, Sapienza R, 2020, The danger of going online only, Physics World, Vol: 33, Pages: 19-19, ISSN: 0953-8585
Sapienza R, 2020, Objective-free excitation of quantum emitters with a laser-written micro parabolic mirror, Applied Physics Letters Photonics
Ta VD, Saxena D, Caixeiro S, et al., 2020, Flexible and tensile microporous polymer fibers for wavelength-tunable random lasing, Nanoscale, Vol: 12, Pages: 12357-12363, ISSN: 2040-3364
Polymer micro-/nanofibers, due to their low-cost and mechanical flexibility, are attractive building blocks for developing lightweight and flexible optical circuits. They are also versatile photonic materials for making various optical resonators and lasers, such as microrings, networks and random lasers. In particular, for random lasing architectures, the demonstrations to-date have mainly relied on fiber bundles whose properties are hard to tune post-fabrication. Here, we demonstrate the successful implementation of an inverted photonic glass structure with monodisperse pores of 1.28 μm into polymer fibers with diameter ranging from 10 to 60 μm. By doping organic dye molecules into this structure, individual fibers can sustain random lasing under optical pulse excitation. The dependence of lasing characteristics, including lasing spectrum and lasing threshold on fiber diameter are investigated. It is found that the lasing emission red-shifts and the threshold decreases with increasing fiber diameter. Furthermore, owing to the mechanical flexibility, the lasing properties can be dynamically changed upon stretching, leading to a wavelength-tunability of 5.5 nm. Our work provides a novel architecture for random lasers which has the potential for lasing tunability and optical sensing.
Reshef O, Aharonovich I, Armani AM, et al., 2020, How to organize an online conference, Nature Reviews Materials, Vol: 5, Pages: 253-256, ISSN: 2058-8437
The first online-only meeting in photonics, held on 13 January 2020, was a resounding success, with 1100 researchers participating remotely to discuss the latest advances in photonics. Here, the organizers share their tips and advice on how to organize an online conference.
Morozov S, Pensa EL, Khan AH, et al., 2020, Electrical control of single-photon emission in highly-charged individual colloidal quantum dots, Publisher: arXiv
Electron transfer to an individual quantum dot promotes the formation ofcharged excitons with enhanced recombination pathways and reduced lifetimes.Excitons with only one or two extra charges have allowed for the development ofvery efficient quantum dot lasing [1] and the understanding of blinkingdynamics [2], while charge transfer management has yielded single quantum dotLEDs [3], LEDs with reduced efficiency roll-off [4], and enabled studies ofcarrier and spin dynamics [5]. Here, by room-temperature time-resolvedexperiments on individual giant-shell CdSe/CdS quantum dots, we show theelectrochemical formation of highly charged excitons containing more thantwelve electrons and one hole. We report control of intensity blinking, as wellas a deterministic manipulation of quantum dot photodynamics, with an observed210-fold increase of the decay rate, accompanied by 12-fold decrease of theemission intensity, all while preserving single-photon emissioncharacteristics. These results pave the way for deterministic control over thecharge state, and room-temperature decay-rate engineering for colloidal quantumdot-based classical and quantum communication technologies.
Morozov S, Vezzoli S, Khan AH, et al., 2020, Objective-free excitation of quantum emitters with a laser-written micro parabolic mirror, Publisher: arXiv
The efficient excitation of quantum sources such as quantum dots or singlemolecules requires high NA optics which is often a challenge in cryogenics, orin ultrafast optics. Here we propose a 3.2 um wide parabolic mirror, with a 0.8um focal length, fabricated by direct laser writing on CdSe/CdS colloidalquantum dots, capable of focusing the excitation light to a sub-wavelength spotand to extract the generated emission by collimating it into a narrow beam.This mirror is fabricated via in-situ volumetric optical lithography, which canbe aligned to individual emitters, and it can be easily adapted to othergeometries beyond the paraboloid. This compact solid-state transducer fromfar-field to the emitter has important applications in objective-free quantumtechnologies.
Sortino L, Brooks M, Zotev PG, et al., 2020, Dielectric nano-antennas for strain engineering in atomically thin two-dimensional semiconductors, Publisher: arXiv
Atomically thin two-dimensional semiconducting transition metaldichalcogenides (TMDs) can withstand large levels of strain before theirirreversible damage occurs. This unique property offers a promising route forcontrol of the optical and electronic properties of TMDs, for instance bydepositing them on nano-structured surfaces, where position-dependent straincan be produced on the nano-scale. Here, we demonstrate strain-inducedmodifications of the optical properties of mono- and bilayer TMD WSe$_2 $placed on photonic nano-antennas made from gallium phosphide (GaP).Photoluminescence (PL) from the strained areas of the TMD layer is enhancedowing to the efficient coupling with the confined optical mode of thenano-antenna. Thus, by following the shift of the PL peak, we deduce thechanges in the strain in WSe$_2$ deposited on the nano-antennas of differentradii. In agreement with the presented theory, strain up to $\approx 1.4 \%$ isobserved for WSe$_2$ monolayers. We also estimate that $>3\%$ strain isachieved in bilayers, accompanied with the emergence of a direct bandgap inthis normally indirect-bandgap semiconductor. At cryogenic temperatures, wefind evidence of the exciton confinement in the most strained nano-scale partsof the WSe$_2$ layers, as also predicted by our theoretical model. Our results,of direct relevance for both dielectric and plasmonic nano-antennas, show thatstrain in atomically thin semiconductors can be used as an additional parameterfor engineering light-matter interaction in nano-photonic devices.
Septiadi D, Barna V, Saxena D, et al., 2020, Biolasing from individual cells in a low-Q resonator enables spectral fingerprinting, Advanced Optical Materials, Vol: 8, Pages: 1-8, ISSN: 2195-1071
Lasing from cells has recently been subject of thorough investigation because of the potential for sensitive and fast biosensing. Yet, lasing from individual cells has been studied in high‐quality resonators, resulting in limited dependence of the lasing properties on the cellular microenvironment. Here, lasing is triggered by cells floating in a low quality factor resonator composed of a disposable poly(methyl methacrylate) (PMMA) cell counting‐slide, hence in absence of conventional high‐reflectivity optical cavities. The exceptional spectral narrowing and the steep slope increase in the input–output energy diagram prove occurrence of laser action in presence of cells. The observed biolasing is an intrinsically dynamic signal, with large fluctuations in intensity and spectrum determined by the optical properties of the individual cell passing through the pump beam. Numerical simulations of the scattering efficiency rule out the possibility of optical feedback from either WGM (whispering gallery mode) or multiple scattering within the cell, and point to the enhanced directional scattering field as the crucial contribution of cells to the laser action. Finally, principal component analysis of lasing spectra measured from freely diffusing cells yields spectral fingerprints of cell populations, which allows discriminating cancer from healthy Rattus glial cells with high degree of confidence.
Toan VN, Nhat VP, Hanh HM, et al., 2019, Protein-based microsphere biolasers fabricated by dehydration, SOFT MATTER, Vol: 15, Pages: 9721-9726, ISSN: 1744-683X
Sortina L, Zotev PG, Mignuzzi S, et al., 2019, Enhanced light-matter interaction in an atomically thin semiconductor coupled with dielectric nano-antennas, Nature Communications, Vol: 50, Pages: 1-8, ISSN: 2041-1723
Unique structural and optical properties of atomically thin transition metal dichalcogenides (TMDs) enable in principle their efficient coupling to photonic cavities having the optical mode volume below the diffraction limit. So far, this has only been demonstrated by coupling TMDs with plasmonic modes in metallic nano-structures, which exhibit strong energy dissipation limiting their potential applications in devices. Here, we present an alternative approach for realisation of ultra-compact cavities interacting with two-dimensional semiconductors: we use mono- and bilayer TMD WSe2 coupled to low-loss high-refractive-index gallium phosphide (GaP) nano-antennas. We observe a photoluminescence (PL) enhancement exceeding 104 compared with WSe2 placed on the planar GaP, and trace its origin to a combination of enhancement of the spontaneous light emission rate, favourable modification of the PL directionality and enhanced optical excitation efficiency, all occurring as a result of WSe2 coupling with strongly confined photonic modes of the nano-antennas. Further effect of the coupling is observed in the polarisation dependence of WSe2 PL, and in the Raman scattering signal enhancement exceeding 103. Our findings reveal high-index dielectric nano-structures as a promising platform for engineering light-matter coupling in two-dimensional semiconductors.
Sapienza R, 2019, Determining random lasing action, Nature Reviews Physics, Vol: 1, Pages: 690-695, ISSN: 2522-5820
Random lasing — for which disorder is exploited to enhance stimulated emission — has emerged as a paradigmatic phenomenon of complex lasers. Random lasers feature unique properties such as tunable coherence and reconfigurable spectral emission. Nevertheless, their complexity sets them apart from conventional lasers, making it challenging to determine whether random lasing is occurring. In this Expert Recommendation, I discuss experimental methods required to properly assess and demonstrate random lasing action.
Bruno V, DeVault C, Vezzoli S, et al., 2019, Negative refraction in time-varying, strongly-coupled plasmonic antenna-ENZ systems, Publisher: arXiv
Time-varying metasurfaces are emerging as a powerful instrument for thedynamical control of the electromagnetic properties of a propagating wave. Herewe demonstrate an efficient time-varying metasurface based on plasmonicnano-antennas strongly coupled to an epsilon-near-zero (ENZ) deeplysub-wavelength film. The plasmonic resonance of the metal resonators stronglyinteracts with the optical ENZ modes, providing a Rabi level spitting of ~30%.Optical pumping at frequency {\omega} induces a nonlinear polarisationoscillating at 2{\omega} responsible for an efficient generation of a phaseconjugate and a negative refracted beam with a conversion efficiency that ismore than four orders of magnitude greater compared to the bare ENZ film. Theintroduction of a strongly coupled plasmonic system therefore provides a simpleand effective route towards the implementation of ENZ physics at the nanoscale
Sortino L, Zotev PG, Mignuzzi S, et al., 2019, Enhanced light-matter interaction in an atomically thin semiconductorcoupled with dielectric nano-antennas
Unique structural and optical properties of atomically thin transition metaldichalcogenides (TMDs) enable in principle their efficient coupling to photoniccavities having the optical mode volume below the diffraction limit. So far,this has only been demonstrated by coupling TMDs with plasmonic modes inmetallic nano-structures, which exhibit strong energy dissipation limitingtheir potential applications in devices. Here, we present an alternativeapproach for realisation of ultra-compact cavities interacting withtwo-dimensional semiconductors: we use mono- and bilayer TMD WSe$_2$ coupled tolow-loss high-refractive-index gallium phosphide (GaP) nano-antennas. Weobserve a photoluminescence (PL) enhancement exceeding 10$^4$ compared withWSe$_2$ placed on the planar GaP, and trace its origin to a combination ofenhancement of the spontaneous light emission rate, favourable modification ofthe PL directionality and enhanced optical excitation efficiency, all occurringas a result of WSe$_2$ coupling with strongly confined photonic modes of thenano-antennas. Further effect of the coupling is observed in the polarisationdependence of WSe$_2$ PL, and in the Raman scattering signal enhancementexceeding 10$^3$. Our findings reveal high-index dielectric nano-structures asa promising platform for engineering light-matter coupling in two-dimensionalsemiconductors.
Mignuzzi S, Cambiasso J, Vezzoli S, et al., 2019, Dielectric nanocavities with enhanced local density of states
We present inverse-designed lossless dielectric nanocavities with enhanced local density of optical states. Photon counting statistics from fluorescent molecules allows determining strong field confinement and single-molecule detection at micromolar concentration in liquid.
Mignuzzi S, Vezzoli S, Horsley SAR, et al., 2019, Nanoscale design of the local density of optical states, Nano Letters, Vol: 19, Pages: 1613-1617, ISSN: 1530-6984
We propose a design concept for tailoring the local density of optical states (LDOS) in dielectric nanostructures, based on the phase distribution of the scattered optical fields induced by point-like emitters. First we demonstrate that the LDOS can be expressed in terms of a coherent summation of constructive and destructive contributions. By using an iterative approach, dielectric nanostructures can be designed to effectively remove the destructive terms. In this way, dielectric Mie resonators, featuring low LDOS for electric dipoles, can be reshaped to enable enhancements of 3 orders of magnitude. To demonstrate the generality of the method, we also design nanocavities that enhance the radiated power of a circular dipole, a quadrupole, and an arbitrary collection of coherent dipoles. Our concept provides a powerful tool for high-performance dielectric resonators and affords fundamental insights into lightmatter coupling at the nanoscale.
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