Browsing by Author "Freire-Fernández, Francisco"

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  • Converting an organic light-emitting diode from blue to white with bragg modes
    (2019-10-08) Daskalakis, Konstantinos S.; Freire-Fernández, Francisco; Moilanen, Antti J.; Van Dijken, Sebastiaan; Törmä, Päivi
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Organic light-emitting diodes (OLEDs) have been established as versatile light sources that allow for easy integration in large-area surfaces and flexible substrates. In addition, the low fabrication cost of OLEDs renders them particularly attractive as general lighting sources. Current methods for the fabrication of white-light OLEDs rely on the combination of multiple organic emitters and/or the incorporation of multiple cavity modes in a thick active medium. These architectures introduce formidable challenges in both device design and performance improvements, namely, the decrease of efficiency with increasing brightness (efficiency roll-off) and short operational lifetime. Here we demonstrate, for the first time, white-light generation in an OLED consisting of a sub-100 nm thick blue single-emissive layer coupled to the photonic Bragg modes of a dielectric distributed Bragg reflector (DBR). We show that the Bragg modes, although primarily located inside the DBR stack, can significantly overlap with the emissive layer, thus efficiently enhancing emission and outcoupling of photons at selected wavelengths across the entire visible light spectrum. Moreover, we show that color temperature can be tuned by the DBR parameters, offering great versatility in the optimization of white-light emission spectra.
  • Energy Efficient Single Pulse Switching of [Co/Gd/Pt]N Nanodisks Using Surface Lattice Resonances
    (2023-02-03) Vergès, Maxime; Perumbilavil, Sreekanth; Hohlfeld, Julius; Freire-Fernández, Francisco; Le Guen, Yann; Kuznetsov, Nikolai; Montaigne, François; Malinowski, Gregory; Lacour, Daniel; Hehn, Michel; van Dijken, Sebastiaan; Mangin, Stéphane
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The impact of plasmonic surface lattice resonances on the magneto-optical properties and energy absorption efficiency has been studied in arrays of [Co/Gd/Pt]N multilayer nanodisks. Varying the light wavelength, the disk diameter, and the period of the array, it is demonstrated that surface lattice resonances allow all-optical single pulse switching of [Co/Gd/Pt]N nanodisk arrays with an energy 400% smaller than the energy needed to switch a continuous [Co/Gd/Pt]N film. Moreover, the magneto-optical Faraday effect is enhanced at the resonance condition by up to 5,000%. The influence of the disk diameter and array period on the amplitude, width and position of the surface lattice resonances is in qualitative agreement with theoretical calculations and opens the way to designing magnetic metasurfaces for all-optical magnetization switching applications.
  • Lasing in Ni Nanodisk Arrays
    (2019-05-28) Pourjamal, Sara; Hakala, Tommi K.; Nečada, Marek; Freire-Fernández, Francisco; Kataja, Mikko; Rekola, Heikki; Martikainen, Jani Petri; Törmä, Päivi; Van Dijken, Sebastiaan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.
  • Magnetic on–off switching of a plasmonic laser
    (2022-01) Freire-Fernández, Francisco; Cuerda, Javier; Daskalakis, Konstantinos S.; Perumbilavil, Sreekanth; Martikainen, Jani Petri; Arjas, Kristian; Törmä, Päivi; van Dijken, Sebastiaan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The nanoscale mode volumes of surface plasmon polaritons have enabled plasmonic lasers and condensates with ultrafast operation1–4. Most plasmonic lasers are based on noble metals, rendering the optical mode structure inert to external fields. Here we demonstrate active magnetic-field control over lasing in a periodic array of Co/Pt multilayer nanodots immersed in an IR-140 dye solution. We exploit the magnetic nature of the nanoparticles combined with mode tailoring to control the lasing action. Under circularly polarized excitation, angle-resolved photoluminescence measurements reveal a transition between the lasing action and non-lasing emission as the nanodot magnetization is reversed. Our results introduce magnetization as a means of externally controlling plasmonic nanolasers, complementary to modulation by excitation5, gain medium6,7 or substrate8. Further, the results show how the effects of magnetization on light that are inherently weak can be observed in the lasing regime, inspiring studies of topological photonics9–11.
  • Plasmon-induced demagnetization and magnetic switching in nickel nanoparticle arrays
    (2018-02-12) Kataja, Mikko; Freire-Fernández, Francisco; Witteveen, Jorn P.; Hakala, Tommi K.; Törmä, Päivi; Van Dijken, Sebastiaan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report on the manipulation of magnetization by femtosecond laser pulses in a periodic array of cylindrical nickel nanoparticles. By performing experiments at different wavelengths, we show that the excitation of collective surface plasmon resonances triggers demagnetization in zero field or magnetic switching in a small perpendicular field. Both magnetic effects are explained by plasmon-induced heating of the nickel nanoparticles to their Curie temperature. Model calculations confirm the strong correlation between the excitation of surface plasmon modes and laser-induced changes in magnetization.
  • Surface-plasmon-polariton-driven narrow-linewidth magneto-optics in ni nanodisk arrays
    (2020-01-01) Freire-Fernández, Francisco; Kataja, Mikko; Van Dijken, Sebastiaan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The field of magnetoplasmonics exploits interactions between light and magnetic matter at the nanoscale for light manipulation and resonant magneto-optics. One of the great challenges of this field is overcoming optical losses in magnetic metals. Here, we exploit surface plasmon polaritons (SPPs) excited at the interface of an SiO2/Au bilayer to induce strong magneto-optical responses on the Ni nanodisks of a periodic array. Using a reference system made of Au nanodisks, we show that optical losses in Ni hardly broaden the linewidth of SPP-driven magneto-optical signals. Loss mitigation is attained because the free electrons in the Ni nanodisks are driven into forced oscillations away from their plasmon resonance. By varying the SiO2 layer thickness and lattice constant of the Ni nanodisk array, we demonstrate tailoring of intense magneto-optical Kerr effects with a spectral linewidth down to ~25 nm. Our results provide important hints on how to circumvent optical losses and enhance magneto-optical signals via the design of off-resonance magnetoplasmonic driving mechanisms.