arXiv subjects

Ievgeniia Chaban

Publications and source records attributed to Ievgeniia Chaban.

4 recordsLinked to original sources

arXiv2026

Equilibrium gigahertz acoustics reveals long-range confinement in liquids

Understanding how the mechanical properties of liquids confined within nanometer-scale gaps differ from bulk behavior is central to biophysics, lubrication, catalysis, electrochemistry, and surface science. Yet the characterization of ultrathin confined liquids remains challenging, as many existing approaches rely on destructive or intrusive contact-based techniques, mostly measuring the liquid flow in the low frequency regime. Here, we present a non-invasive, all-optical technique based on ultrafast laser ultrasonics that probes confined liquids at equilibrium in the gigahertz frequency range. The method measures the phase and amplitude of time-domain Brillouin scattering signals transmitted through liquid layers whose thickness is varied step by step with subnanometer effective sampling. Supported by numerical modeling of acoustic propagation and optical detection, these signals allow us to extract the thickness-dependent acoustic velocity and attenuation of confined liquids. We show that nanometric confinement modifies the GHz acoustic response of glycerol, the liquid crystal 8CB, and a butyl-based ionic liquid over unexpectedly long spatial scales. These effects extend from a few nanometers to several tens of nanometers and reveal bound interfacial layers, acoustic stiffening, and enhanced solid-like behavior under confinement. Our results open a route to probing liquid confinement in a scarcely explored regime: dynamically measured at gigahertz frequencies, yet sufficiently weakly perturbative to preserve the equilibrium confined state.

cond-mat.soft↗

arXiv2023

Additive Laser Excitation of Giant Nonlinear Surface Acoustic Wave Pulses

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.

cond-mat.mtrl-sci↗

arXiv2022

Nonlinear optical absorption in nanoscale films revealed through ultrafast acoustics

Herein we describe a novel spinning pump-probe photoacoustic technique developed to study nonlinear absorption in thin films. As a test case, an organic polycrystalline thin film of quinacridone, a well-known pigment, with a thickness in the tens of nanometers range, is excited by a femtosecond laser pulse which generates a time-domain Brillouin scattering signal. This signal is directly related to the strain wave launched from the film into the substrate and can be used to quantitatively extract the nonlinear optical absorption properties of the film itself. Quinacridone exhibits both quadratic and cubic laser fluence dependence regimes which we show to correspond to two- and three-photon absorption processes. This technique can be broadly applied to materials that are difficult or impossible to characterize with conventional transmittance-based measurements including materials at the nanoscale, prone to laser damage, with very weak nonlinear properties, opaque or highly scattering.

physics.optics↗

arXiv2017

Time-domain Brillouin scattering assisted by diffraction gratings

Absorption of ultrashort laser pulses in a metallic grating deposited on a transparent sample launches coherent compression/dilatation acoustic pulses in directions of different orders of acoustic diffraction. Their propagation is detected by the delayed laser pulses, which are also diffracted by the metallic grating, through the measurement of the transient intensity change of the first order diffracted light. The obtained data contain multiple frequency components which are interpreted by considering all possible angles for the Brillouin scattering of light achieved through the multiplexing of the propagation directions of light and coherent sound by the metallic grating. The emitted acoustic field can be equivalently presented as a superposition of the plane inhomogeneous acoustic waves, which constitute an acoustic diffraction grating for the probe light. Thus, the obtained results can also be interpreted as a consequence of probe light diffraction by both metallic and acoustic gratings. The realized scheme of time-domain Brillouin scattering with metallic grating operating in reflection mode provides access to acoustic frequencies from the minimal to the maximal possible in a single experimental configuration for the directions of probe light incidence and scattered light detection. This is achieved by monitoring of the backward and forward Brillouin scattering processes in parallel. Applications include measurements of the acoustic dispersion, simultaneous determination of sound velocity and optical refractive index, and evaluation of the samples with a single direction of possible optical access.

physics.app-ph↗