In this Letter, we calculate the optical and magneto- optical reflectivity in a dielectric/gap/ferromagnet excited by ap-polarized monochromatic optical beam through the prism (Otto configuration) as a function of the angle of incidence 6 and the gap thickness d . Besides the well-known surface plasmon polariton (SPP resonance at d lambda ), we find a new, to the best of our knowledge, resonance with a nanometric gap d 10 nm at a large 6 80 degrees. Both resonances display pronounced resonant behavior in the transverse magneto- optical Kerr effect (T-MOKE). (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Femtosecond lasers are routinely used for inducing local modification, including nanostructuring, and ultrafast laser spectroscopy in solids. However, these studies are often being performed separately making the unveiling of exciting physical properties of laser-fabricated materials out of reach. Here, we present an all-optical platform combining the fabrication of nano to micrometer size single-shot "femtosecond-laser-delamination" membranes or cavities of ferromagnetic thin films and multilayers together with their quasi in situ characterization using the Abbe-limited interferometric, ultrafast scanning photo-acoustic and magneto-plasmonic microscopies. Ferromagnetic nickel and iron cavities display high-Q acoustic resonances providing access to long-lived ultrahigh frequency coherent phonon modes in the above 100 GHz frequency range. Cavities in cobalt-gold bilayers allow for magnetically controlled surface plasmon resonance experiments in the Otto configuration, which is otherwise very difficult to implement experimentally. Quantitative experimental characterization of functional magnetic cavities, supported by the numerical modeling of all experimental data, opens an avenue to design and fabricate tunable nanoscaled femtosecond-laser-delamination architectures in thin films and multilayers.

The quest for manipulation of magnetization on ultrafast timescales faces many technological challenges. Successful achievement thereof could shed light on novel fundamental phenomena, such as inertial magnetization dynamics, as well as accelerate technological advancements towards higher information processing rates. One of the recent approaches towards this end concerns excitation of magnetization dynamics via laser-induced picosecond acoustic pulses, which has given birth to the field of ultrafast magneto-acoustics. Considerable progress has been made in the field from an experimental point of view, as well as from the perspective of theoretical modelling. In this talk, we aim to review some of the aforementioned progress and propose the frequency dependent cooperativity parameter (strong coupling regime) to measure the efficiency of resonantly enhanced phonon-magnon interactions in the GHz-to-THz frequency range.

It has been shown that when drops fall on a solid surface, the physicochemical properties of water change. After drops fall on a solid surface, water saturated with atmospheric gases luminesces in the blue region of the spectrum. The luminescence intensity decreases exponentially after exposure. The concentration of gases (molecular oxygen and carbon dioxide) in water decreases. In this case, both the size and the number of nano-sized gas bubbles in the water do not change. It has been established that when drops fall on a solid surface in water saturated with atmospheric gases, hydrogen peroxide and hydroxyl radicals are formed. As the fall height increases, the intensity of generation of hydrogen peroxide and hydroxyl radical increases. The formation of hydrogen peroxide is probably associated with two independent mechanisms.

A dynamic trapping of Lamb modes with a frequency cutoff was achieved through local heating of an elastic plate using a cw laser. The relatively small variations in material stiffness resulting from the temperature rise proved effective at capturing waves within the heated region, which behaved like a potential well for specific Lamb modes. These trapped modes corresponded precisely to discrete frequencies predicted by the time-independent Schr & ouml;dinger equation, reminiscent of the principle quantum number. The number of trapped modes hinges on both the width and depth of the laser-induced thermal potential well, with these variables interrelated via Heisenberg's uncertainty principle. Furthermore, we observed a highquality factor (Q factor of approximately 260) attributed to the trapped wave motion within the potential well, offering significant promise for highly precise nondestructive evaluation of thermal and mechanical properties of materials.

We report on measurements of the anisotropy of velocities and attenuation of GHz-frequency acoustic phonons in a cubic MgO crystal at room temperature. They are used to quantify the strong anisotropy of the Grüneisen parameter and calculate the attenuation anisotropy for Rayleigh surface acoustic waves. These observations constitute important building blocks for better understanding of ultrafast laser-based magneto-acoustic and nonlinear acoustic experiments at ultrahigh frequencies.

We revisit the quantitative analysis of the ultrafast magnetoacoustic experiment in a freestanding nickel thin film by Kim and Bigot [J.-W. Kim and J.-Y. Bigot, Phys. Rev. B 95, 144422 (2017)] by applying our recently proposed approach of magnetic and acoustic eigenmode decomposition. We show that the application of our modeling to the analysis of time-resolved reflectivity measurements allows for the determination of amplitudes and lifetimes of standing perpendicular acoustic phonon resonances with unprecedented accuracy. The acoustic damping is found to scale as proportional to omega 2 for frequencies up to 80 GHz, and the peak amplitudes reach 10-3. The experimentally measured magnetization dynamics for different orientations of an external magnetic field agrees well with numerical solutions of magnetoelastically driven magnon harmonic oscillators. Symmetry-based selection rules for magnon-phonon interactions predicted by our modeling approach allow for the unambiguous discrimination between spatially uniform and nonuniform modes, as confirmed by comparing the resonantly enhanced magnetoelastic dynamics simultaneously measured on opposite sides of the film. Moreover, the separation of timescales for (early) rising and (late) decreasing precession amplitudes provide access to magnetic (Gilbert) and acoustic damping parameters in a single measurement.

Phase velocity of surface acoustic waves(SAWs) is frequency dependent when propagate on medium with inhomogeneous elasticity over depth. In this work, frequency dependent Time-of-Flight (ToF) variation of SAWs induced by a local and dynamic heating was applied for measurement of temperature dependent shear modulus. Laser-generated broad-band SAWs propagated through the material with elastic properties and density modified by dynamic inhomogeneous temperature field induced by a millisecond laser heating. Sample with spatial dependent material properties introduces phase velocity dispersion in the SAW propagation. As consequence, ToF of SAW becomes frequency dependent. Frequency dependent ToF variation curves at two time instants respected to laser heating were measured by time-frequency analysis together with a differential technique. Free fitted parameters, temperature dependent shear modulus and surface temperature distribution were evaluated by solving the inverse problem by fitting the experimental ToF variation curves into the theoretical ones by means of the differential evolution method. The inversed temperature dependent parameter of shear modulus of Ti-6Al-4V alloy was in good agreement with literature value.

Femtosecond (fs) time-resolved magneto-optics is applied to investigate laser-excited ultrafast dynamics of one-dimensional nickel gratings on fused silica and silicon substrates for a wide range of periodicities Λ = 400-1500 nm. Multiple surface acoustic modes with frequencies up to a few tens of GHz are generated. Nanoscale acoustic wavelengths Λ/n have been identified as nth-spatial harmonics of Rayleigh surface acoustic wave (SAW) and surface skimming longitudinal wave (SSLW), with acoustic frequencies and lifetimes being in agreement with theoretical calculations. Resonant magnetoelastic excitation of the ferromagnetic resonance (FMR) by SAW's third spatial harmonic, and, most interestingly fingerprints of the parametric resonance at 1/2 SAW frequency have been observed. Numerical solutions of Landau-Lifshitz-Gilbert (LLG) equation magnetoelastically driven by complex polychromatic acoustic fields quantitatively reproduce all resonances at once. Thus, our results provide a solid experimental and theoretical base for a quantitative understanding of ultrafast fs-laser-driven magnetoacoustics and tailoring the magnetic-grating-based metasurfaces at the nanoscale.

The laser ultrasonics technique perfectly fits the needs for non-contact, non-invasive, non-destructive mechanical probing of samples of mm to nm sizes. This technique is however limited to the excitation of low-amplitude strains, below the threshold for optical damage of the sample. In the context of strain engineering of materials, alternative optical techniques enabling the excitation of high amplitude strains in a non-destructive optical regime are seeking. We introduce here a non-destructive method for laser-shock wave generation based on additive superposition of multiple laser-excited strain waves. This technique enables strain generation up to mechanical failure of a sample at pump laser fluences below optical ablation or melting thresholds. We demonstrate the ability to generate nonlinear surface acoustic waves (SAWs) in Nb:SrTiO$_3$ substrates, at typically 1 kHz repetition rate, with associated strains in the percent range and pressures close to 100 kbars. This study paves the way for the investigation of a host of high-strength SAW-induced phenomena, including phase transitions in conventional and quantum materials, plasticity and a myriad of material failure modes, chemistry and other effects in bulk samples, thin layers, or two-dimensional materials.

While most ultrafast time-resolved optical pump-probe experiments in magnetic materials reveal the spatially homogeneous magnetization dynamics of ferromagnetic resonance (FMR), here we explore the magneto-elastic generation of GHz-to-THz frequency spin waves (exchange magnons). Using analytical magnon oscillator equations, we apply time-domain and frequency-domain approaches to quantify the results of ultrafast time-resolved optical pump-probe experiments in free-standing ferromagnetic thin films. Simulations show excellent agreement with the experiment, provide acoustic and magnetic (Gilbert) damping constants and highlight the role of symmetry-based selection rules in phonon-magnon interactions. The analysis is extended to hybrid multilayer structures to explore the limits of resonant phonon-magnon interactions up to THz frequencies.

Anomalies in reflection from periodic structures, well known in optics, result from either the transition from specular reflection to diffraction of light (Rayleigh's anomaly) or by coupling to the leaky surface mode supported by the structure (Wood's anomaly). Experimental observation and detailed analysis of both kinds of anomalies are presented here in the case of antisymmetric Lamb wave (A0) incidence at the 1D periodic structure located along the edge of the elastic plate. A structure with a strong phononic effect has been chosen, which enables the separation of both effects in terms of frequency. Another distinct feature of elastic waves in the periodic structure considered in this work is the existence of several localized modes, which leads to the multiple Wood's anomalies. Here, we report the experimental observation of double Wood's anomaly in addition to the Rayleigh's type of anomaly.

We introduce a non-destructive method for laser-shock wave generation based on additive superposition of multiple laser-excited strain waves. This technique enables strain generation up to mechanical failure of the sample at pump laser fluences below material ablation or melting thresholds. We demonstrate the ability to generate nonlinear surface acoustic waves (SAWs) in Nb:SrTiO 3 substrates, at typically 1 kHz repetition rate, with associated strains in the percent range. This study paves the way for the investigation of a host of high-strength SAW-induced phenomena, including phase transitions, fatigue, chemistry, and other effects in bulk samples, thin layers, or two-dimensional materials.

We analyze resonant magnetoelastic interactions between standing perpendicular spin wave modes (exchange magnons) and longitudinal acoustic phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all metal layers control the frequencies and eigenmodes of acoustic vibrations. The design proposed here allows for achieving and tuning the spectral and spatial mode overlap between phonons and magnons that results in their strong resonant interaction. Realistic simulations for gold-nickel multilayers show that sweeping the external magnetic field should allow for observing resonantly enhanced interactions between individual magnon and phonon modes in a broad range of frequencies spanning from tens of gigahertz up to several hundreds of gigahertz, which can be finely tuned through the multilayer design. Our results would enable the systematic study and the deep understanding of resonantly enhanced magnetoelastic coupling between individual phonon and magnon modes up to frequencies of great contemporary fundamental and applied interest.

The laser ultrasound (LU) technique has been used to determine dispersion curves for surface acoustic waves (SAW) propagating in AlScN/Al2O3 systems. Polar and non-polar Al0.77Sc0.23N thin films were prepared by magnetron sputter epitaxy on Al2O3 substrates and coated with a metal layer. SAW dispersion curves have been measured for various propagation directions on the surface. This is easily achieved in LU measurements since no additional surface structures need to be fabricated, which would be required if elastic properties are determined with the help of SAW resonators. Variation of the propagation direction allows for efficient use of the system's anisotropy when extracting information on elastic properties. This helps to overcome the complexity caused by a large number of elastic constants in the film material. An analysis of the sensitivity of the SAW phase velocities (with respect to the elastic moduli and their dependence on SAW propagation direction) reveals that the non-polar AlScN films are particularly well suited for the extraction of elastic film properties. Good agreement is found between experiment and theoretical predictions, validating LU as a non-destructive and fast technique for the determination of elastic constants of piezoelectric thin films.

Nonlinear acoustic waves are considered that have displacements localized at the tip of an elastic wedge. The evolution equation governing their propagation is discussed and compared with its analogues pertaining to nonlinear acoustic surface and bulk waves. Solitary wave solutions of the evolution equation have been determined numerically for the cases of two rectangular edges which may be viewed as generated by splitting a half-space, consisting of crystalline silicon, into two quarter-spaces. For these two geometries, the kernel in the nonlinear terms of the evolution equation has been calculated from the second-order and third-order elastic constants of silicon, and weak dispersion due to tip truncation has been considered. Solitary pulse shapes have been computed and collisions of solitary pulses have been simulated for various relative speeds of the two collision partners. Collision scenarios for the two wedge geometries were found to differ considerably. Special attention is paid to the peculiar interaction of two initially identical solitary pulses.

Dispersion of surface acoustic waves (SAWs) caused by a dynamic surface heating–cooling cycle has been applied for evaluation of thermal properties. A laser-generated broad-band SAW pulse is propagated through the material whose elastic properties and density were modified by the dynamic inhomogeneous temperature field produced by laser heating and subsequent cooling. A sample with depth-dependent material properties introduces a phase velocity dispersion in SAW propagation. Dispersion was measured by a differential technique, which helped to isolate the thermally induced dispersion and eliminate the contributions of other possible sources of dispersion. The dispersion curves were measured at several time instants, which allowed evaluation of the following parameters: thermal diffusivity, temperature dependence of the shear modulus, and the temperature magnitude. The inverse problem was solved by fitting the experimental dispersion curves into the theoretical ones by means of differential evolution techniques.

提出了一种应用神经网络从色散曲线反演材料弹性常数的温度依赖性的方法.采用有限元方法计算了毫秒激光加热铝材料形成的瞬态温度场.在假设不同杨氏模量温度依赖性的条件下,计算了表面波在激光加热区传播时不同的频散曲线.利用正向计算的结果来训练神经网络.神经网络经过训练后,输入材料的表面波频散特性,可反演出材料杨氏模量与温度的关系.为验证该方法的反演能力,对比了不同噪声情况下的反演结果.对比结果表明该方法具有很好的鲁棒性.