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Revealing defects and inhomogeneities of physical and chemical properties beneath a surface or an interface with in-depth nanometric resolution plays a pivotal role for a high degree of reliability in nanomanufacturing processes and in materials science more generally. (1, 2) Nanoscale noncontact depth profiling of mechanical and optical properties of transparent sub-micrometric low-k material film exhibiting inhomogeneities is here achieved by picosecond acoustics interferometry. On the basis of the optical detection through the time-resolved Brillouin scattering of the propagation of a picosecond acoustic pulse, depth profiles of acoustical velocity and optical refractive index are measured simultaneously with spatial resolution of tens of nanometers. Furthermore, measuring the magnitude of this Brillouin signal provides an original method for depth profiling of photoelastic moduli. This development of a new opto-acoustical nanometrology paves the way for in-depth inspection and for subsurface nanoscale imaging of inorganic- and organic-based materials.

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.

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.

Water ice is a molecular solid whose behavior under compression reveals the interplay of covalent bonding in molecules and forces acting between them. This interplay determines high-pressure phase transitions, the elastic and plastic behavior of H 2 O ice, which are the properties needed for modeling the convection and internal structure of the giant planets and moons of the solar system as well as H 2 O-rich exoplanets. We investigated experimentally and theoretically elastic properties and phase transitions of cubic H 2 O ice at room temperature and high pressures between 10 and 82 GPa. The time-domain Brillouin scattering (TDBS) technique was used to measure longitudinal sound velocities (V L) in polycrystalline ice samples compressed in a diamond anvil cell. The high spatial resolution of the TDBS technique revealed variations of V L caused by elastic anisotropy, allowing us to reliably determine the fastest and the slowest sound velocity in a single crystal of cubic H 2 O ice and thus to evaluate existing equations of state. Pressure dependencies of the single-crystal elastic moduli C ij (P) of cubic H 2 O ice to 82 GPa have been obtained which indicate its hardness and brittleness. These results were compared with ab initio calculations. It is suggested that the transition from molecular ice VII to ionic ice X occurs at much higher pressures than proposed earlier, probably above 80 GPa.

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...

Very high amplitude nonlinear surface acoustic wave pulses with 20 -100 ns duration and acoustic Mach numbers up to 0.003 were excited in fused silica by nanosecond laser pulses acting on a strongly absorbing overlayer. Absolute measurements were performed with a calibrated dual-probelaser deflection setup. The formation of shock fronts during propagation and nonlinear broadening of the wave form were observed for the first time. Three nonlinear acoustic constants were evaluated and compared with values resulting from previously measured third-order elastic moduli.[S0031-9007(97)03749-6] PACS numbers: 68.35.Gy, 03.40.Kf, 43.35. + d, 62.65. + k The propagation velocity of Rayleigh-type surface acoustic waves (SAWs) with small amplitude does not depend on the frequency or the amplitude for a homogeneous solid [1]. Therefore SAWs with a plane front retain their shape and amplitude during propagation, provided the attenuation is negligibly small. For SAWs with large amplitudes the propagation velocity starts to depend on the particle velocity of the substance and, as a result, different parts of the SAW profile move with distinct velocities. This causes characteristic changes of the pulse shape. Nonlinear effects have been extensively studied for bulk waves, including transformation of the wave profile and formation of a shock front [2][3][4][5]. Nonlinear phenomena for SAWs have been studied to a much smaller extent, although they are of importance for strong seismic waves generated by earthquakes as well as in signal processing devices [6][7][8][9]. In previous experiments SAWs were excited using interdigital transducers, which allowed only the region of relatively weak nonlinear effects to be reached. The pulsed laser technique makes it possible to obtain very high amplitudes of elastic waves, as was demonstrated with laser-driven bulk shock waves [10]. For the excitation of short SAW pulses the laser pulses should be in sharp focus on the surface. As the laser fluence is increased the screening effect due to the onset of optical breakdown and plasma formation usually prevents an effective input of the laser energy into the material. In previous studies of linear elastic constants of thin films [11,12] and also anisotropy [13] with laser-generated broadband SAW pulses only relatively small amplitudes were excited.In this Letter we report on the laser generation, propagation, and detection of SAWs with high amplitudes (up to the limit of cracking) in fused silica. The SAW pulses were generated with nanosecond laser pulses through a thin strongly absorbing layer as shown in Fig. 1 [14]. The nonlinear SAW pulses were registered with a cw laser dual-probe-beam deflection (PBD) setup which allowed the measurement at two different distances. The propagation of nonlinear SAWs was numerically simulated using a general theoretical model accurate to the elastic moduli of the third order for an isotropic solid without any a priori assumptions on the depth profile of the SAW.The elastic moduli of the second order of fused ...

Fragmentation of DNA is an essential step for many biological applications including the preparation of next-generation sequencing (NGS) libraries. As sequencing technologies push the limits towards single cell and single molecule resolution, it is of great interest to reduce the scale of this upstream fragmentation step. Here we describe a miniaturized DNA shearing device capable of processing sub-microliter samples based on acoustic shearing within a microfluidic chip. A strong acoustic field was generated by a Langevin-type piezo transducer and coupled into the microfluidic channel via the flexural lamb wave mode. Purified genomic DNA, as well as covalently cross-linked chromatin were sheared into various fragment sizes ranging from ∼180 bp to 4 kb. With the use of standard PDMS soft lithography, our approach should facilitate the integration of additional microfluidic modules and ultimately allow miniaturized NGS workflows.