Optinen superresoluutio käyttäen hyväksi elektronisuihkua integroidussa valo-elektronimikroskopiassa

We have developed an optical superresolution method based on electronbleaching of fluorophores in integrated light-electron microscopy. The main advantage of this novel superresolution method is that the non-fluorescent ultrastructure of the sample can be revealed by the simultaneously acquired SEM image. Furthermore, as the fluorescence superresolution image is based on an electron-beam-induced modification of the specimen, by "switching off" fluorescent probes, both the fluorescence and SEM image are recorded with perfect spatial overlap - being a great advantage for correlative imaging. The superresolution method is demonstrated with fluorescent microspheres, having a diameter of 40--50~nm. Their bleaching behaviour is studied as a function of various exposure parameters, and we show that the bleaching rate is mostly dependent on the injected electron dose and electron landing energy. The superresolution experiments are performed in an integrated light-electron microscope platform (SECOM, Delmic), with which fluorescence emission of the sample can be monitored while the electron beam scans over it. The method is successfully demonstrated with the fluorescent beads on ITO-coated glass and TEM-grid substrates. We have achieved a localization precision of approximately 100~nm of the fluorescent beads, and an image resolution of 160~nm -- well beyond the diffraction limit of light. The method may eventually provide an excellent tool for researchers doing correlative light-electron microscopy in modern life sciences, such as cell and molecular biology.Olemme kehittäneet optisen superresoluutiomenetelmän, joka perustuu fluoresoivien molekyylien elektronisuihkuvalkaisuun integroidussa valo-elektronimikroskopiassa. Tämän aivan uudenlaisen superresoluutiomenetelmän suurin etu on, että näytteen ei-fluoresoiva hienorakenne pystytään paljastamaan samaan aikaan otetun elektronimikroskooppikuvan avulla. Koska fluoresenssikuva kerätään ”sammuttamalla” fluoresoivia molekyylejä elektronisuihkun avulla, on fluoresenssi- ja elektronimikroskooppikuvien koordinaatisto täsmälleen sama, mikä on suureksi hyödyksi ajatellen korreloivaa kuvantamista. Superresoluutiomenetelmä demonstroidaan fluoresoivien mikropallojen avulla, joiden halkaisija on 40--50~nm. Ensimmäiseksi mikropallojen sammumiskäyttäytymistä tutkitaan eri valkaisuparametrien funktiona. Näytämme, että valkaisunopeus riippuu enimmäkseen syötetystä elektroniannoksesta ja elektronien energiasta. Superresoluutiokokeet toteutetaan integroidulla valo-elektronimikroskooppialustalla (SECOM, Delmic), jossa fluoresenssisignaalia voidaan tarkkailla samalla kun elektronisuihku pyyhkii näytteen pintaa. Menetelmän osoitetaan toimivan ITO-päällystetyillä lasialustoilla, sekä TEM-hiloilla. Olemme saavuttaneet n. 100~nm tarkkuuden fluoresoivien mikropallojen lokalisaatiossa, fluoresenssikuvan resoluution ollessa n. 160~nm, joka on reilusti valon diffraktiorajan alapuolella. Menetelmä voi aikanaan tarjota erinomaisen työkalun tutkijoille, jotka hyödyntävät korreloivaa valo-elektronimikroskopiaa biotieteissä, kuten solu- ja molekyylibiologiassa

Laserointi ja Bosen-Einsteinin kondensaatio plasmonihiloissa heikon ja vahvan kytkennän alueella

Plasmonics takes advantage of the coupling of light to charge oscillations in metals, which enables breaking the diffraction limit and confining the optical fields in sub-wavelength volumes. The extreme field confinement can greatly enhance the light-matter interaction of photons and quantum emitters, such as atoms and molecules. In this dissertation, I have studied metal nanoparticles arranged in regular two-dimensional lattices, combined with organic dye molecules. The aim is to study strong light-matter interaction as well as lasing and condensation phenomena in these plasmonic lattices. I have fabricated the nanoparticle arrays with electron beam lithography that allows precise control of the shape and size of the nanoparticle, and periodicity and geometry of the lattice. Optical modes of the plasmonic lattices are characterized by white light transmission and reflection measurements. Angular and spatial distribution of the photoluminescence intensity is measured, together with the corresponding spectra, under optical excitation of 50 fs laser pulses. I have developed a rate-equation model to understand the dynamics of stimulated processes. In Publication I, we show strong-coupling between the lattice modes and the molecular excitations. Lasing action in both bright and dark modes of the plasmonic lattice is demonstrated in Publication II. In Publication III, we probe the dynamics of ultrafast laser pulse generation and observe a modulation speed of more than 100 GHz. The pulse build-up time and pulse duration is measured with a double-pump spectroscopy technique that utilizes the non-linearity of photoluminescence at the lasing threshold.In Publication IV, we demonstrate Bose-Einstein condensation of excitations in the plasmonic lattice, the first realization of condensation in plasmonic systems. We establish a measurement scheme that provides a direct access for observing thermalization and the accumulation of macroscopic population to the energy ground state. The scheme utilizes open-cavity character and propagating modes in the plasmonic lattice. Thermalization is explained with recurrent absorption-emission cycles in the dye molecules forming a thermal bath, in the weak coupling regime. In Publication V, we achieve a Bose-Einstein condensate of strongly-coupled lattice plasmons. This condensate is hundred-thousand fold brighter in luminescence intensity compared to the first one. We observe a distinct thermalized population distribution extending over one decade, in time integrated luminescence signal. Multiple condensation peaks are observed at the lowest energy states with a thermal tail at higher energies that follows Maxwell-Boltzmann distribution at room temperature (333 K). The thermalization occurs in a 200 fs timescale, which is explained with stimulated processes and strong coupling. Room-temperature operation, significant robustness and high luminescence of the samples provide an excellent platform for future studies of luminous driven-dissipative condensates, non-equilibrium quantum dynamics and topological photonics.Plasmoniikka hyödyntää valon kytkeytymistä elektronien värähtelyihin metallisissa nanorakenteissa mahdollistaen sähkömagneettisten kenttien keskittämisen valon aallonpituutta pienempiin tilavuuksiin. Energian lokalisaatio vahvistaa merkittävästi valon ja materian vuorovaikutusta. Tässä väitöskirjassa tutkin metallisia nanopartikkelihiloja, jotka on päällystetty kerroksella väriainemolekyylejä. Tavoitteena on tutkia hilan optisten muotojen ja molekyylien vahvaa kytkentää, sekä laserointia ja kondensoitumista. Olen valmistanut nanopartikkelihilat elektronisuihkulitografialla, joka mahdollistaa yksittäisen nanopartikkelin muodon ja koon, sekä hilaperiodin ja geometrian tarkan kontrolloinnin nanometrimittakaavassa. Karakterisoin hilan optiset resonanssit transmissio ja reflektio- mittauksilla. Mittaan näytteen säteilyintensiteetin paikka- ja kulmajakauman, sekä vastaavat luminesenssispektrit, kun fluoresoivaa väriainetta viritetään 50 fs mittaisilla laserpulsseilla. Mallinnan näytteessä tapahtuvia stimuloituja prosesseja rakentamallani tasapainoyhtälömallilla. Julkaisussa I näytämme vahvan kytkennän hilan optisten resonanssien ja molekyylien välillä. Julkaisussa II saamme näytteen laseroimaan sekä hilan kirkkaassa että pimeässä resonanssimuodossa. Julkaisussa III tutkimme laseroinnin dynamiikkaa ja saavutamme yli 100 GHz modulaationopeuden, jolla kehittämämme hilalaser säteilee pulssin, sen jälkeen kun se on viritetty. Hyödynnämme dynamiikan tutkimuksessa spektroskopiatekniikkaa, jossa systeemi viritetään kahdella perättäisellä laserpulssilla, joiden erotusta ajassa voidaan säätää. Julkaisussa IV demonstroimme ensimmäistä kertaa maailmassa Bosen-Einsteinin kondensaation plasmonisessa systeemissä, ja se esiintyy huoneenlämpötilassa. Pystymme mittaamaan luminesenssispektrin evoluution paikan funktiona, jossa näemme näytteessä virittyvien kvasipartikkelien termalisoitumisen sekä makroskooppisen populaation muodostumisen alimmalle energiatilalle. Kvasipartikkelit ovat osittain valoa ja osittain elektronien värähtelyä nanopartikkeleissa. Termalisoitumisen eli Bosen-Einsteinin statistiikan mukaisen termisen tasapainotilan saavuttamisen tekee mahdolliseksi edestakainen emissio-absorptiosykli väriainemolekyyleissä. Julkaisussa V saavutamme Bosen-Einsteinin kondensaatin vahvan kytkennän alueella. Tämä kondensaatti säteilee satatuhatta kertaa kirkkaampana kuin ensimmäinen kondensaatti. Mittausten perusteella termalisaatio tapahtuu ultranopeasti 200 fs aikaskaalassa, mikä selittää sen, että Bosen-Einsteinin statistiikan mukainen tasapainojakauma näkyy aikaintegroidussa signaalissa. Tämä siitäkin huolimatta, että ilman väriaineen vahvistavaa vaikutusta kvasipartikkelit hajoavat ja vuotavat valona näytteeltä ulos jopa alle 100 fs ajassa. Toiminta huoneenlämpötilassa, kondensaatin kirkkaus sekä näytteen kestävyys luovat erinomaisen alustan säteilevien kvasipartikkelikondensaattien, kvanttidynamiikan sekä topologisen fotoniikan tutkimukselle

Strong coupling between organic dye molecules and lattice modes of a dielectric nanoparticle array

Plasmonic structures interacting with light provide electromagnetic resonances that result in a high degree of local field confinement, enabling the enhancement of light-matter interaction. Plasmonic structures typically consist of metals, which, however, suffer from very high ohmic losses and heating. High-index dielectrics, meanwhile, can serve as an alternative material due to their low-dissipative nature and strong scattering abilities. We studied the optical properties of a system composed of all-dielectric nanoparticle arrays covered with a film of organic dye molecules (IR-792) and compared these dielectric arrays with metallic nanoparticle arrays. We tuned the light-matter interaction by changing the concentration in the dye film and reported the system to be in the strong coupling regime. We observed a Rabi splitting between the surface lattice resonances of the nanoparticle arrays and the absorption line of the dye molecules of up to 253 and 293 meV, for the dielectric and metallic nanoparticles, respectively. The Rabi splitting depends linearly on the square root of the dye molecule concentration, and we further assessed how the Rabi splitting depends on the film thickness for a low dye molecule concentration. For thinner films of thicknesses up to 260 nm, we observed no visible Rabi splitting. However, a Rabi splitting evolved at thicknesses from 540 to 990 nm. We performed finite-difference time-domain simulations to analyze the near-field enhancements for the dielectric and metallic nanoparticle arrays. The electric fields were enhanced by a factor of 1200 and 400, close to the particles for gold and amorphous silicon, respectively, and the modes extended over half a micron around the particles for both materials.Peer reviewe

Strong coupling between organic dye molecules and lattice modes of a dielectric nanoparticle array

Plasmonic structures interacting with light provide electromagnetic resonances that result in a high degree of local field confinement, enabling the enhancement of light-matter interaction. Plasmonic structures typically consist of metals, which, however, suffer from very high ohmic losses and heating. High-index dielectrics, meanwhile, can serve as an alternative material due to their low-dissipative nature and strong scattering abilities. We studied the optical properties of a system composed of all-dielectric nanoparticle arrays covered with a film of organic dye molecules (IR-792) and compared these dielectric arrays with metallic nanoparticle arrays. We tuned the light-matter interaction by changing the concentration in the dye film and reported the system to be in the strong coupling regime. We observed a Rabi splitting between the surface lattice resonances of the nanoparticle arrays and the absorption line of the dye molecules of up to 253 and 293 meV, for the dielectric and metallic nanoparticles, respectively. The Rabi splitting depends linearly on the square root of the dye molecule concentration, and we further assessed how the Rabi splitting depends on the film thickness for a low dye molecule concentration. For thinner films of thicknesses up to 260 nm, we observed no visible Rabi splitting. However, a Rabi splitting evolved at thicknesses from 540 to 990 nm. We performed finite-difference time-domain simulations to analyze the near-field enhancements for the dielectric and metallic nanoparticle arrays. The electric fields were enhanced by a factor of 1200 and 400, close to the particles for gold and amorphous silicon, respectively, and the modes extended over half a micron around the particles for both materials

Ultrafast Pulse Generation in an Organic Nanoparticle-Array Laser

| openaire: EC/H2020/745115/EU//OPLDNanoscale coherent light sources offer potentially ultrafast modulation speeds, which could be utilized for novel sensors and optical switches. Plasmonic periodic structures combined with organic gain materials have emerged as promising candidates for such nanolasers. Their plasmonic component provides high intensity and ultrafast nanoscale-confined electric fields, while organic gain materials offer fabrication flexibility and a low acquisition cost. Despite reports on lasing in plasmonic arrays, lasing dynamics in these structures have not been experimentally studied yet. Here we demonstrate, for the first time, an organic dye nanoparticle-array laser with more than a 100 GHz modulation bandwidth. We show that the lasing modulation speed can be tuned by the array parameters. Accelerated dynamics is observed for plasmonic lasing modes at the blue side of the dye emission.Peer reviewe

Controlling quantum dot emission by plasmonic nanoarrays

Peer reviewe

Sub-picosecond thermalization dynamics in condensation of strongly coupled lattice plasmons

Bosonic condensates offer exciting prospects for studies of non-equilibrium quantum dynamics. Understanding the dynamics is particularly challenging in the sub-picosecond timescales typical for room temperature luminous driven-dissipative condensates. Here we combine a lattice of plasmonic nanoparticles with dye molecule solution at the strong coupling regime, and pump the molecules optically. The emitted light reveals three distinct regimes: one-dimensional lasing, incomplete stimulated thermalization, and two-dimensional multimode condensation. The condensate is achieved by matching the thermalization rate with the lattice size and occurs only for pump pulse durations below a critical value. Our results give access to control and monitoring of thermalization processes and condensate formation at sub-picosecond timescale. Understanding the sub-picosecond dynamics of driven-dissipative condensates of interacting bosons is challenging. Here the authors combine a lattice of plasmonic nanoparticles with a dye molecule solution in strong coupling and reveal distinct lasing, stimulated thermalization, and condensation regimes.Peer reviewe

Lasing and condensation in plasmonic lattices

I review our recent findings on lasing / condensation in plasmonic nanoparticle lattices1-5. The system properties can be tailored with high precision, including the lasing / condensation energies, linewidths, as well as the dimensionality of the feedback. For a 2-dimensional (2-D) square lattice, we identify lasing in the bright and the dark mode of the system1. By reducing the dimensionality to 1-D we observe the dark mode lasing2. In broken symmetry 2-dimensional rectangular lattices, we observe multimode lasing3. In honeycomb lattices with hexagonal symmetry, we observe 6 beams with specific off-normal angles and polarization properties corresponding to six-fold symmetry of such a lattice4. Finally, I review our recent studies in plasmonic Bose-Einstein condensation in plasmonic lattices5.Peer reviewe

Bose–Einstein condensation in a plasmonic lattice

| openaire: EC/H2020/745115/EU//OPLDBose–Einstein condensation is a remarkable manifestation of quantum statistics and macroscopic quantum coherence. Superconductivity and superfluidity have their origin in Bose–Einstein condensation. Ultracold quantum gases have provided condensates close to the original ideas of Bose and Einstein, while condensation of polaritons and magnons has introduced novel concepts of non-equilibrium condensation. Here, we demonstrate a Bose–Einstein condensate of surface plasmon polaritons in lattice modes of a metal nanoparticle array. Interaction of the nanoscale-confined surface plasmons with a room-temperature bath of dye molecules enables thermalization and condensation in picoseconds. The ultrafast thermalization and condensation dynamics are revealed by an experiment that exploits thermalization under propagation and the open-cavity character of the system. A crossover from a Bose–Einstein condensate to usual lasing is realized by tailoring the band structure. This new condensate of surface plasmon lattice excitations has promise for future technologies due to its ultrafast, room-temperature and on-chip nature.Peer reviewe