Vasily V. Temnov

Ultrafast acousto-magneto-plasmonics

Surface plasmon polaritons (SPP or SP) are electromagnetic waves propagating along metal dielectric interfaces and existing over a wide range of frequencies. They have become popular because of their sub-wavelength confinement and the possibility to perform ultrasensitive optical measurements. Driven by tremendous progress in nanofabrication techniques and ultrafast laser technologies the applications of SP nanooptics extend beyond the border of nanoplasmonics. Here we review how using novel hybrid multilayer structures combining different functionalities allows to develop active plasmonic devices and new metrologies. Magneto-plasmonics, acousto-plasmonics and generation of high-energy photoelectrons using ultrashort SP pulses represent a few examples how the combination of ideas developed in the individual subfields can be used to generate new knowledge suggesting plenty of exciting applications in nanophotonics. Investigation of plasmonic devices beyond the diffraction limit [1] represents a topical research direction in active plasmonics with major progress reported on the development of SP-based amplifiers and lasers [2]. After the original theoretical proposal by Krasavin and Zheludev to use structural thermally induced phase transitions in gallium-coated plasmonic waveguides [3] many other ways to actively control SP propagation have been realized in the experiment including electro-optic effect in dielectric overlayers [4], optical excitation of semiconductor quantum dots [5, 6] or magnetization switching in magneto-plasmonic materials [7]. Whereas nanoplasmonics with quantum dots has been extensively discussed elsewhere [2, 8] here we review the progress in magneto-plasmonics, ultrafast acousto-plasmonic and magneto-acoustic interactions. This development is largely driven by continuously improving nanofabrication techniques and borrowing the ideas from other well-established research directions. Despite of being very different in nature these studies follow the same idea: to explore various light-matter interactions in metallic nanostructures at the true nanoscale, within the tiny skin depth of light at visible and near IR frequencies. Development of hybrid ultrafast nanophotonic devices for future telecommunication and data recording technologies represents the final goal of these research activities. The basic knowledge of the spatial distribution of electromagnetic field at interfaces supporting propagating SP waves appears to be inevitably necessary to understand the underlying physics. A typical hybrid noble

Complete ground state gain recovery after ultrashort double pulses in quantum dot based semiconductor optical amplifier

Gain recovery dynamics are studied in electrically pumped quantum dot (QD) based semiconductor optical amplifiers (SOAs) after amplification of double femtosecond laser pulses using ultrafast pump-probe spectroscopy with heterodyne detection. The authors observe a distinct change in gain recovery in the ground state when a significant excited state population is achieved. A complete gain recovery is found when two 150fs pulses with 5ps time delay pass through the SOA in resonance to the ground state under high injection currents of 80–100mA. The obtained results open the way for ultrafast (>200GHz) operation in p-doped QD based SOAs at 1.3μm telecommunications wavelengths.

Ultrafast imaging interferometry at femtosecond- laser-excited surfaces

�2 rad and amplitude changes 1% with micrometer spatial resolution 1 m. Interferograms are processed using a 2D-Fourier transform algorithm. We discuss the image formation and the physical interpretation of the measured interferograms. The technique is applied to measure transient changes of a GaAs surface irradiated with intense femtosecond laser pulses with fluences near the ablation threshold.

Surface plasmon interferometry : measuring group velocity of surface plasmons

Optical transmission spectroscopy on metal films with slit-groove pairs is conducted. Spectra of the light transmitted through the slit exhibit Fabry-Perot-type interference fringes due to surface plasmons propagating between the slit and the groove. The spectral dependence of the period of interference fringes is used to determine the group velocity of surface plasmons on flat gold and silver surfaces.

Enhancement of the magnetic modulation of surface plasmon polaritons in Au/Co/Au films

The deposition of a dielectric overlayer on top of Au/Co/Au multilayer films can significantly enhance the magnetic field induced modulation of the surface plasmon polariton (SPP) wave vector. This enhancement is analyzed as a function of the thickness of the dielectric overlayer and the associated SPP electromagnetic field confinement and redistribution. The decrease in SPP propagation distance is taken into account by analyzing an adequate figure of merit.

New Concept for Magnetization Switching by Ultrafast Acoustic Pulses

It is shown theoretically that a single acoustic pulse, a few picoseconds long, can reverse magnetization in a magnetostrictive material Terfenol-D. Following giant magnetoelastic changes of free energy density, the magnetization vector is ejected from a local in-plane energy minimum and decays into another minimum. For an acoustic pulse duration significantly shorter than magnetization precession period τac≪Tprec, the switching threshold is determined by the acoustic pulse area, i.e., pulse integral in the time domain, similar to coherent phenomena in optics. Simulation results are summarized in a magnetoacoustic switching diagram and discussed in the context of all-optical magnetization switching by circularly polarized light pulses.

Femtosecond surface plasmon interferometry

We demonstrate femtosecond plasmonic interferometry with a novel geometry. The plasmonic microinterferometer consists of a tilted slit-groove pair. This arrangement allows for (i) interferometric measurements at a single wavelength with a single microinterferometer and (ii) unambiguous discrimination between changes in real and imaginary parts of the metal dielectric function. The performance is demonstrated by monitoring the sub-picosecond dynamics of hot electrons in gold.

Photon statistics in the cooperative spontaneous emission

The second-order photon correlation function g((2))(tau) of photons emitted by a continuously pumped ensemble of N two-level systems coupled to a single-mode optical cavity well below the lasing threshold is investigated theoretically. A giant photon bunching is found for N < 10 emitters as the microscopic counterpart of spontaneous emission noise driven quasi-periodic superradiant pulse sequences in macroscopic systems of large numbers of emitters N >> 1. The phenomenon of giant photon bunching is preserved even for N = 2 and can be explained by the cooperative evolution via dark and bright two-atom states resulting into emission of superradiant photon pairs. The sensitivity of g((2)) to microscopic dephasing processes and resonance frequency detuning opens the door for photon bunching spectroscopy.

Transient Grating Spectroscopy in Magnetic Thin Films: Simultaneous Detection of Elastic and Magnetic Dynamics

Surface magnetoelastic waves are coupled elastic and magnetic excitations that propagate along the surface of a magnetic material. Ultrafast optical techniques allow for a non-contact excitation and detection scheme while providing the ability to measure both elastic and magnetic components individually. Here we describe a simple setup suitable for excitation and time resolved measurements of high frequency magnetoelastic waves, which is based on the transient grating technique. The elastic dynamics are measured by diffracting a probe laser pulse from the long-wavelength spatially periodic structural deformation. Simultaneously, a magnetooptical measurement, either Faraday or Kerr effect, is sensitive to the out-of-plane magnetization component. The correspondence in the response of the two channels probes the resonant interaction between the two degrees of freedom and reveals their intimate coupling. Unraveling the observed dynamics requires a detailed understanding of the spatio-temporal evolution of temperature, magnetization and thermo-elastic strain in the ferromagnet. Numerical solution of thermal diffusion in two dimensions provides the basis on which to understand the sensitivity in the magnetooptic detection.

Nonlinear Surface Magnetoplasmonics in Kretschmann Multilayers

Nonlinear magnetoplasmonics aims to utilize plasmonic excitations to control the mechanisms and tailor the efficiencies of nonlinear light frequency conversion at the nanoscale. We investigate the mechanisms of magnetic second-harmonic generation in hybrid gold–cobalt–silver multilayer structures, which support propagating surface plasmon polaritons at both fundamental and second-harmonic frequencies. Using magneto-optical spectroscopy in Kretschmann geometry, we show that the huge magneto-optical modulation of the second-harmonic intensity is dominated by the excitation of surface plasmon polaritons at the second-harmonic frequency, as shown by tuning the optical wavelength over the spectral region of strong plasmonic dispersion. Our proof-of-principle experiment highlights bright prospects of nonlinear magnetoplasmonics and contributes to the general understanding of the nonlinear optics of magnetic surfaces and interfaces.