3D characterization of individual grains of coexisting high-pressure H2O ice phases by time-domain Brillouin scattering

Abstract

Time-domain Brillouin scattering uses ultrashort laser pulses to generate coherent acoustic pulses of picoseconds duration in a solid sample and to follow their propagation in order to image material inhomogeneities with sub-optical depth resolution. The width of the acoustic pulse limits the spatial resolution of the technique along the direction of the pulse propagation to less than several tens of nanometres. Thus, the time-domain Brillouin scattering outperforms axial resolution of the classical frequency-domain Brillouin scattering microscopy, which uses continuous lasers and thermal phonons and which spatial resolution is controlled by light focusing. The technique benefits from the application of the coherent acoustic phonons, and its application has exciting perspectives for the nanoscale imaging in biomedical and material sciences. In this study, we report on the application of the time-domain Brillouin scattering to the 3D imaging of a polycrystal of water ice containing two high-pressure phases. The imaging, accomplished via a simultaneous detection of quasi-longitudinal and quasi-shear waves, provided the opportunity to identify the phase for individual grains and evaluate their crystallographic orientation. Monitoring the propagation of the acoustic waves in two neighbouring grains simultaneously provided an additional mean for the localisation of the grain boundaries.

Sound Velocity Anisotropy and Single‐Crystal Elastic Moduli of MgO to 43 GPa

“…A detailed description of the TDBS technique can be found elsewhere (Decremps et al., 2015; Nikitin et al., 2015). For our experimental geometry, where the CAPs and the probe beam propagated collinearly, the oscillation frequency ( f B ) is proportional to the acoustic wave velocity ( V i ) according to the following equation (Sandeep et al., 2021; Thomsen et al., 1986; Xu et al., 2013): $$${f}_{\mathrm{B}}=\frac{2n{V}_{\mathrm{i}}}{\lambda }$$$ where λ is wavelength of the probe beam in vacuum (800 nm in this work), n is refractive index of the sample material at the same wavelength, and i stands for the acoustic wave type (L for LAW or T for transversal acoustic waves—TAW). It should be noted that LAWs with corresponding frequencies f B were always detected in the collected TDBS signals.…”

“…A detailed description of the TDBS technique can be found elsewhere (Decremps et al, 2015;Nikitin et al, 2015). For our experimental geometry, where the CAPs and the probe beam propagated collinearly, the oscillation frequency (f B ) is proportional to the acoustic wave velocity (V i ) according to the following equation (Sandeep et al, 2021;Thomsen et al, 1986;Xu et al, 2013):…”

“…TDBS, also called picosecond laser ultrasonics (Thomsen et al., 1986; Zhao et al., 2019), can be considered as a combination of the advantages of the two abovementioned techniques: (a) it measures directly and in real time velocities of the stimulated coherent acoustic pulses, CAPs, which guarantees the signal quality (as in conventional ultrasonic technique), (b) it is an all‐optical method which allows measurements at pressures achievable in a DAC (as is the case for the BLS). The further advantage of the TDBS technique is a high axial resolution of the velocity measurements, better than 1 μm (Nikitin et al., 2015; Sandeep et al., 2021; Xu et al., 2021), not accessible for the conventional pulse‐echo ultrasonics and for the BLS method. Power of the TDBS in high‐pressure studies was already proved in earlier publications reporting extraction of complete sets of C ij ( P ) of cubic solids from polycrystalline sample (Kuriakose, Raetz, et al., 2017; Raetz et al., 2019; Xu et al., 2021, 2022).…”

Towards acoustic microscopy at the nanoscale by coupling atomic force microscopy with picosecond ultrasonics

“…Since picosecond acoustics was developed by Thomsen et al [1,2], time-resolved pump-probe spectroscopy has proven to be a very effective way to probe and image nanoscale elastic properties of a wide variety of materials. Employed both, in industrial and fundamental research, it has recently been used to perform elasticity imaging of various systems such as biological cells [3][4][5][6][7][8][9][10] and polycristalline materials [11][12][13]. The generation of acoustic waves with frequencies up to a couple hundred GHz enables achievement of very good in-depth resolution [14].…”

Time-domain Brillouin imaging of sound velocity and refractive index using automated angle scanning

“…The latter technique, known as picosecond ultrasonic interferometry or TDBS (Time-Domain Brillouin Scattering), relies on the photoelastic effect, and has been used for depth profiling and three-dimensional (3D) imaging of the longitudinal sound velocity in transparent samples, including biological cells, assuming a constant refractive index distribution [17] , [18] , [19] , [20] , [21] , [22] , [23] . In addition, various other applications have been suggested for TDBS, such as monitoring polycrystalline aggregates, ion implantation profiles, internal stress distributions, and temperature gradients [24] , [25] , [26] . TDBS has also been used to profile both the refractive index and sound velocity by multiple probe-light incidence angle measurements, but the proposed apparatus is not automated, leading to arduous data acquisition procedures [11] , [27] , [28] .…”