Ultrafast high strain rate acoustic wave measurements at high static pressure in a diamond anvil cell

Abstract

We have used subpicosecond laser pulses to launch ultrahigh strain rate (∼109s−1) nonlinear acoustic waves into a 4:1 methanol-ethanol pressure medium which has been precompressed in a standard diamond anvil cell. Using ultrafast interferometry, we have characterized acoustic wave propagation into the pressure medium at static compression of up to 24GPa. We find that the velocity is dependent on the incident laser fluence, demonstrating a nonlinear acoustic response which may result in a shock wave behavior. We compare our results to low strain rate acoustic data. This technique provides controlled access to regions of thermodynamic phase space that is otherwise difficult to obtain.

Revealing sub-μm and μm-scale textures in H2O ice at megabar pressures by time-domain Brillouin scattering

“…Later this technique has been also realized with picosecond laser pulses instead of femtosecond laser pulses. 31 In the picosecond acoustic interferometry, which is a particular optical pumpprobe technique, the pump laser pulse generates in a light absorbing opto-acoustic transducer picosecond acoustic pulse which propagates through a sample. Since a typical length of picosecond acoustic pulse is in the nanometers to sub-micrometers spatial scale, the technique is perfectly suitable for examination of materials confined in DACs where sample sizes are typically from several tens of micrometers down to a few micrometers and grains in polycrystalline samples are typically below 1 μm in size (Fig.…”

“…30 Thus, measuring the period/frequency of this time-domain Brillouin oscillation provides information on the velocity of the acoustic wave in the sample. In the collinear scattering geometry of the TDBS experiments 28,31 the Brillouin frequency is proportional to the product of sound velocity and of the optical refractive index of the medium at the probe wave length (see Eq. (1) in Results).…”

Anomalous sound velocities in polycrystalline MgO under non-hydrostatic compression

“…The 6 mm sintered MgO was polished to 30 mm, sliced to a 75 × 75 mm square and loaded in a 50 mm thick gasket along with < 1-2 mm diameter ruby spheres (as calibrant) and 4:1 methanol:ethanol (ME) mixture as pressure-transmitting medium. We see no evidence of ME peaks in any of the Brillouin spectra, including at pressures where the ME compressional mode would stand alone [Armstrong et al, 2008]. Ruby spheres also did not give a Brillouin signal.…”

Nonlinear Acoustics at GHz Frequencies in a Viscoelastic Fragile Glass Former

“…In such materials, characteristic pressures ranged from a few to 10-20 GPa, and acoustic Mach numbers defined as M A ¼ u=v 0 , where u is the particle velocity and v 0 the linear acoustic velocity, were subsonic in the range 0.2 < M A < 0.9. Very recently, the propagation of weak shock waves with Mach numbers M A < 0.1 and pressures below the damage threshold of the sample has been observed in thin sapphire slabs through ultrafast optical reflectivity [13], in a 4:1 methanol-ethanol mixture in a diamond anvil cell by ultrafast velocity interferometry [14], in a piezoelectric thin film through terahertz spectroscopy [15], and in a gold film through ultrafast plasmon interferometry [16] and ultrafast optical imaging [17]. In such weakly nonlinear acoustics experiments [18], no variation of the weak shock wave velocity during propagation has been reported to date.…”