We generate in-plane magnetoelastic waves in nickel films using the all-optical transient grating technique. When performed on amorphous glass substrates, two dominant magnetoelastic excitations can be resonantly driven by the underlying elastic distortions, the Rayleigh surface acoustic wave and the surface skimming longitudinal wave. An applied field, oriented in the sample plane, selectively tunes the coupling between magnetic precession and one of the elastic waves, thus demonstrating selective excitation of coexisting, large-amplitude magnetoelastic waves. Analytical calculations based on the Green's function approach corroborate the generation of multiple surface acoustic transients with disparate decay dynamics.

We use the transient grating technique to generate narrow-band, widely tunable, in-plane surface magnetoelastic waves in a nickel film. We monitor both the structural deformation of the acoustic wave and the accompanying magnetic precession and witness their intimate coupling in the time domain. Strikingly, when an in plane magnetic field is applied parallel to the acoustic propagation direction, we witness its resonant coupling to the ferromagnetic resonance. V

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.

The bacterial (Rhodopseudomonas acidophila) photosynthetic peripheral light-harvesting complex of type 2 (LH2) exhibits rich fluorescence spectral dynamics at room temperature. The fluorescence spectrum of individual LH2 shifts either to the blue or to the red during the experimental observation time of a few minutes. These spectral changes are often reversible and occur between levels of a distinctly different peak wavelength. Furthermore, they are accompanied by a change of the spectral line shape. To interpret the dynamics of spectral changes, an energetic disorder model associated with easily explainable structural changes of the protein is proposed. This model assumes that each pigment in the tightly coupled ring of bacteriochlorophylls can be in two states of electronic transition energy due to the protein-pigment interaction. The transition between these structural, and hence spectroscopic, states occurs through the thermally induced conformational potential energy barrier crossing. Although simplified, the model allows us to reproduce the bulk fluorescence spectrum, the distribution of the single-molecule spectral peak wavelength and its changes, and the statistics of the duration of the spectral states. It also provides an intuitively clear picture of possible protein dynamics in LH2. At the same time, it requires additional sophistication since it essentially does not reproduce the red occurrences of single LH2 spectra.

We demonstrate the nonlinear frequency conversion of ferromagnetic resonance (FMR) frequency by optically excited elastic waves in a thin metallic film on dielectric substrates. Time-resolved probing of the magnetization directly witnesses magneto-elastically driven second harmonic generation, sum-and difference frequency mixing from two distinct frequencies, as well as parametric downconversion of each individual drive frequency. Starting from the Landau-Lifshitz-Gilbert equations, we derive an analytical equation of an elastically driven nonlinear parametric oscillator and show that frequency mixing is dominated by the parametric modulation of FMR frequency. PACS numbers:Parametric behaviour emerges in a wide range of periodically driven systems when their parameters are also periodically modulated [1].Examples can be found in nano-optomechanical [2-4] and microelectromechanical systems [5], (spin) wave dynamics [6], quantum circuitry [7], energy harvesting applications [8], and in line with our current report, magneto-mechanical systems [9] including spin pumping capabilities [10]. The utility of parametric behaviour has been shown for quantum limited detection, noise floor reduction or low noise amplification of small signals [2,7].Parametric phenomena in magnetization dynamics have also been extensively studied in the framework of spintronic and magnonic applications [11], where the downconversion of a microwave-driven uniform precession can generate two counter-propagating spin waves of varying frequency and wavevector. The onset of parametric behaviour in these cases is monitored via the enhanced damping and linewidth changes of the ferromagnetic resonance (FMR) precessional motion. Furthermore, time domain probing of FMR precession modulated with multiple microwave electromagnetic fields leads to seeded parametric downconversion [12]. Additional studies along these lines have resulted in the generation and detection of a range of frequency mixing processes of both uniform precessional modes as well as higher energy spin waves [13][14][15], including frequency upand down-conversion.Looking beyond microwave excitation, the overlapping frequency range of (surface) acoustic waves and magnetization precession provides for a unique opportunity to study their interactions and to explore physical processes where coherent elastic deformations could provide the necessary parametric modulation to drive complex magnetization dynamics. In recent years, magnetoelastic interactions have seen a resurgence of interest, and linear coupling between these degrees of freedom have been demonstrated [16][17][18][19][20][21]. To our knowledge, only a single report has discussed the potential for nonlinearities in the magnetoelastic interactions [22].In this report we present experimental evidence for the nonlinear (in the sense of frequency mixing) interaction between multiple coherent elastic deformations and the magnetization precession in a thin ferromagnetic film. To explain our results we perform analytical calculations of...