Imperial College London

ProfessorRiccardoSapienza

Faculty of Natural SciencesDepartment of Physics

Professor of Physics
 
 
 
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Contact

 

+44 (0)20 7594 9577r.sapienza Website

 
 
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Location

 

B913Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

101 results found

Tavakoli N, Spalding R, Lambertz A, Koppejan P, Gkantzounis G, Wan C, Roehrich R, Kontoleta E, Koenderink AF, Sapienza R, Florescu M, Alarcon-Llado Eet al., 2022, Over 65% Sunlight Absorption in a 1 mu m Si Slab with Hyperuniform Texture, ACS PHOTONICS, Vol: 9, Pages: 1206-1217, ISSN: 2330-4022

Journal article

Granchi N, Spalding R, Lodde M, Petruzzella M, Otten FW, Fiore A, Intonti F, Sapienza R, Florescu M, Gurioli Met al., 2022, Near-field investigation of luminescent hyperuniform disordered materials, Advanced Optical Materials, Vol: 10, Pages: 1-9, ISSN: 2195-1071

Disordered photonic nanostructures have attracted tremendous interest in the past three decades, not only due to the fascinating and complex physics of light transport in random media, but also for peculiar functionalities in a wealth of interesting applications. Recently, the interest in dielectric disordered systems has received new inputs by exploiting the role of long-range correlation within scatterer configurations. Hyperuniform photonic materials, that share features of photonic crystals and random systems, constitute the archetype of systems where light transport can be tailored from diffusive transport to a regime dominated by light localization due to the presence of photonic band gap. Here, advantage is taken of the combination of the hyperuniform disordered (HuD) design in slab photonics, the use of embedded quantum dots for feeding the HuD resonances, and near-field hyperspectral imaging with sub-wavelength resolution in the optical range to explore the transition from localization to diffusive transport. It is shown, theoretically and experimentally, that photonic HuD systems support resonances ranging from strongly localized modes to extended modes. It is demonstrated that Anderson-like modes with high Q/V are created, with small footprint, intrinsically reproducible and resilient to fabrication-induced disorder, paving the way for a novel photonic platform for quantum applications.

Journal article

Saxena D, Arnaudon A, Cipolato O, Gaio M, Quentel A, Yaliraki S, Pisignano D, Camposeo A, Barahona M, Sapienza Ret al., 2022, Sensitivity and spectral control of network lasers

Recently, random lasing in complex networks has shown efficient lasing overmore than 50 localised modes, promoted by multiple scattering over theunderlying graph. If controlled, these network lasers can lead tofast-switching multifunctional light sources with synthesised spectrum. Here,we observe both in experiment and theory high sensitivity of the network laserto the spatial shape of the pump profile, with mode intensity variation of upto 280% for a non-homogeneous 7% pump decrease. We solve the nonlinearequations within the steady state ab-initio laser theory (SALT) approximationover a graph and we show selective lasing of around 90% of the top modes,effectively programming the spectrum of the lasing networks. In our experimentswith polymer networks, this high sensitivity enables control of the lasingspectrum through non-uniform pump patterns. We propose the underlyingcomplexity of the network modes as the key element behind efficient spectralcontrol opening the way for the development of optical devices with wide impactfor on-chip photonics for communication, sensing and computation.

Journal article

Galiffi E, Tirole R, Yin S, Li H, Vezzoli S, Huidobro PA, Silveirinha MG, Sapienza R, Alu A, Pendry JBet al., 2022, Photonics of time-varying media, ADVANCED PHOTONICS, Vol: 4

Journal article

Morozov S, Vezzoli S, Myslovska A, Giacomo AD, Mortensen NA, Moreels I, Sapienza Ret al., 2021, Purifying single photon emission from a CdSe/CdS colloidal quantum dot, Publisher: ArXiv

Colloidal quantum dots are robust and flexible single photon emitters forroom-temperature applications, but their purity is strongly reduced at highpump powers, due to multiexcitonic emission which cannot be easily filtered dueto the photo-luminescence spectral broadening at room temperature. Giant-shellquantum dots feature a large blueshift of the biexciton spectrum due toelectron-hole wave function engineering and piezoelectric charge separation,which can be exploited for spectral separation of the single exciton from themultiexciton emission. Here, by spectral filtering, we show that we can recoveran excellent single-photon emission, with $g_2{(0)} < 0.05$ (resolutionlimited), even at high pump powers above saturation of the exciton emission.The bright and pure single-photon generation shown here has importantapplications in quantum information technology and random-number generation.

Working paper

Glass D, Quesada-Cabrera R, Bardey S, Promdet P, Sapienza R, Keller V, Maier SA, Caps V, Parkin IP, Cortes Eet al., 2021, Probing the role of atomic defects in photocatalytic systems through photoinduced enhanced raman scattering, ACS Energy Letters, Vol: 6, Pages: 4273-4281, ISSN: 2380-8195

Even in ultralow quantities, oxygen vacancies (VO) drastically impact keyproperties of metal oxide semiconductors, such as charge transport, surface adsorption,and reactivity, playing central roles in functional materials performance. Currentmethods used to investigate VO often rely on specialized instrumentation under far fromideal reaction conditions. Hence, the influence of VO generated in situ during catalyticprocesses has yet to be probed. In this work, we assess in situ extrinsic surface VOformation and lifetime under photocatalytic conditions which we compare tophotocatalytic performance. We show for the first time that lifetimes of in situ generatedatomic VO play more significant roles in catalysis than their concentration, with strongcorrelations between longer-lived VO and higher photocatalytic activity. Our resultsindicate that enhanced photocatalytic efficiency correlates with goldilocks VOconcentrations, where VO densities must be just right to encourage carrier transportwhile avoiding charge carrier trapping.

Journal article

Sortino L, Zotev PG, Phillips CL, Brash AJ, Cambiasso J, Marensi E, Fox AM, Maier SA, Sapienza R, Tartakovskii AIet al., 2021, Bright single photon emitters with enhanced quantum efficiency in a two-dimensional semiconductor coupled with dielectric nano-antennas, Nature Communications, Vol: 12, ISSN: 2041-1723

Single photon emitters in atomically-thin semiconductors can be deterministically positioned using strain induced by underlying nano-structures. Here, we couple monolayer WSe2 to high-refractive-index gallium phosphide dielectric nano-antennas providing both optical enhancement and monolayer deformation. For single photon emitters formed on such nano-antennas, we find very low (femto-Joule) saturation pulse energies and up to 104 times brighter photoluminescence than in WSe2 placed on low-refractive-index SiO2 pillars. We show that the key to these observations is the increase on average by a factor of 5 of the quantum efficiency of the emitters coupled to the nano-antennas. This further allows us to gain new insights into their photoluminescence dynamics, revealing the roles of the dark exciton reservoir and Auger processes. We also find that the coherence time of such emitters is limited by intrinsic dephasing processes. Our work establishes dielectric nano-antennas as a platform for high-efficiency quantum light generation in monolayer semiconductors.

Journal article

Dagdeviren OE, Glass D, Sapienza R, Cortes E, Maier SA, Parkin IP, Grutter P, Quesada-Cabrera Ret al., 2021, The effect of photoinduced surface oxygen vacancies on the charge carrier dynamics in TiO2 films, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 8348-8354, ISSN: 1530-6984

Metal-oxide semiconductors (MOS) are widely utilized for catalytic and photocatalytic applications in which the dynamics of charged carriers (e.g., electrons, holes) play important roles. Under operation conditions, photoinduced surface oxygen vacancies (PI-SOV) can greatly impact the dynamics of charge carriers. However, current knowledge regarding the effect of PI-SOV on the dynamics of hole migration in MOS films, such as titanium dioxide, is solely based upon volume-averaged measurements and/or vacuum conditions. This limits the basic understanding of hole-vacancy interactions, as they are not capable of revealing time-resolved variations during operation. Here, we measured the effect of PI-SOV on the dynamics of hole migration using time-resolved atomic force microscopy. Our findings demonstrate that the time constant associated with hole migration is strongly affected by PI-SOV, in a reversible manner. These results will nucleate an insightful understanding of the physics of hole dynamics and thus enable emerging technologies, facilitated by engineering hole-vacancy interactions.

Journal article

Ta VD, Caixeiro S, Saxena D, Sapienza Ret al., 2021, Biocompatible Polymer and Protein Microspheres with Inverse Photonic Glass Structure for Random Micro‐Biolasers, Advanced Photonics Research, Vol: 2, Pages: 2170025-2170025, ISSN: 2699-9293

Journal article

Ta VD, Caixeiro S, Saxena D, Sapienza Ret 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.

Journal article

Tirole R, Attavar T, Dranczewski J, Galiffi E, Pendry J, Maier S, Vezzoli S, Sapienza Ret 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.

Conference paper

Tirole R, Attavar T, Dranczewski J, Galiffi E, Pendry J, Maier S, Vezzoli S, Sapienza Ret 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.

Conference paper

Sortino L, Zotev PG, Sapienza R, Maier SA, Tartakovskii AIet al., 2021, Enhanced light-matter interaction in atomically thin semiconductors and 2D single photon emitters coupled to dielectric nano-antennas

Conference paper

Sortino L, Zotev PG, Sapienza R, Maier SA, Tartakovskii Aet 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

Conference paper

Lee JB, Walker H, Li Y, Nam TW, Rakovich A, Sapienza R, Jung YS, Nam YS, Maier SA, Cortes Eet 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.

Journal article

Rubino A, Huq T, Dranczewski J, Lozano G, Calvo ME, Vezzoli S, Miguez H, Sapienza Ret 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.

Journal article

Persano L, Szukalski A, Gaio M, Moffa M, Salvadori G, Sznitko L, Camposeo A, Mysliwiec J, Sapienza R, Mennucci B, Pisignano Det 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.

Journal article

Sapienza R, Morozov S, Vezzoli S, Maier Set 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.

Journal article

Kalinic B, Cesca T, Mignuzzi S, Jacassi A, Balasa IG, Maier SA, Sapienza R, Mattei Get 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.

Journal article

Collins H, Barnes B, Sapienza R, 2020, The danger of going online only, Physics World, Vol: 33, Pages: 19-19, ISSN: 0953-8585

Journal article

Sapienza R, 2020, Objective-free excitation of quantum emitters with a laser-written micro parabolic mirror, Applied Physics Letters Photonics

Journal article

Ta VD, Saxena D, Caixeiro S, Sapienza Ret 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.

Journal article

Reshef O, Aharonovich I, Armani AM, Gigan S, Grange R, Kats MA, Sapienza Ret 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.

Journal article

Morozov S, Pensa EL, Khan AH, Polovitsyn A, Cortes E, Maier SA, Vezzoli S, Moreels I, Sapienza Ret 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.

Working paper

Morozov S, Vezzoli S, Khan AH, Moreels I, Sapienza Ret 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.

Working paper

Sortino L, Brooks M, Zotev PG, Genco A, Cambiasso J, Mignuzzi S, Maier SA, Burkard G, Sapienza R, Tartakovskii AIet 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.

Working paper

Septiadi D, Barna V, Saxena D, Sapienza R, Genovese D, De Cola Let 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.

Journal article

Toan VN, Nhat VP, Hanh HM, Dung CD, Hai HL, Sapienza R, Van-Duong Tet al., 2019, Protein-based microsphere biolasers fabricated by dehydration, SOFT MATTER, Vol: 15, Pages: 9721-9726, ISSN: 1744-683X

Journal article

Sortina L, Zotev PG, Mignuzzi S, Cambiasso J, SChmidt D, Genco A, Abmann M, Bayer M, Maier SA, Sapienza R, Tartakovskii AIet 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.

Journal article

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.

Journal article

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