Plane photoacoustic wave generation in liquid water using irradiation of terahertz pulses

Abstract

We demonstrate photoacoustic wave propagation with a plane wavefront in liquid water using a terahertz (THz) laser pulse. The THz light can effectively generate the photoacoustic wave in water because of strong absorption via a stretching vibration mode of the hydrogen bonding network. The excitation of a large-area water surface irradiated by loosely focused THz light produces a plane photoacoustic wave. This is in contrast with conventional methods using absorbers or plasma generation using near-infrared laser light. The photoacoustic wave generation and plane wave propagation are observed using a system with a THz free-electron laser and shadowgraph imaging. The plane photoacoustic wave is generated by incident THz light with a small radiant exposure of < 1 mJ/cm2 and delivered 600 times deeper than the penetration depth of THz light for water. The THz-light-induced plane photoacoustic wave offers great advantages to non-invasive operations for industrial and biological applications as demonstrated in our previous report (Yamazaki et al. in Sci Rep 10:9008, 2020).

Gre factors prevent thermal and mechanical stresses induced by terahertz irradiation during transcription

“…When high‐power THz pulses are focused on a material, various nonlinear photophysical and photochemical processes are induced. Previously, we have shown that THz pulses effectively generate acoustic waves (pressure waves) in liquid water because the pulse energy is strongly absorbed via the stretching vibration mode of the hydrogen bonding network, and thus is instantaneously confined in a small volume (Tsubouchi et al., 2020; Yamazaki et al., 2020). Subsequently, the energy of the micropulse is released as an acoustic wave with a discontinuous change in pressure into the liquid via the thermoelastic effect (Tsubouchi et al., 2020).…”

“…Previously, we have shown that THz pulses effectively generate acoustic waves (pressure waves) in liquid water because the pulse energy is strongly absorbed via the stretching vibration mode of the hydrogen bonding network, and thus is instantaneously confined in a small volume (Tsubouchi et al., 2020; Yamazaki et al., 2020). Subsequently, the energy of the micropulse is released as an acoustic wave with a discontinuous change in pressure into the liquid via the thermoelastic effect (Tsubouchi et al., 2020). Such an acoustic wave is not localized on the solution surface but can propagate a few millimeters into the aqueous solution (Tsubouchi et al., 2020).…”

“…Subsequently, the energy of the micropulse is released as an acoustic wave with a discontinuous change in pressure into the liquid via the thermoelastic effect (Tsubouchi et al., 2020). Such an acoustic wave is not localized on the solution surface but can propagate a few millimeters into the aqueous solution (Tsubouchi et al., 2020). This indicates that a rapid and local pressure increase stemming from the acoustic wave is a likely reason for the THz‐induced effects on transcription, in addition to the T‐jump.…”

“…Estimated increases in temperature Δ T just after a single micropulse of 26 µJ/cm 2 irradiated the aqueous sample were plotted against the depth. The spacing between wavepackets of the acoustic wave was estimated to be 55 μm on average (Tsubouchi et al., 2020)…”

Terahertz-induced martensitic transformation in partially stabilized zirconia

“…To populate the TA phonon mode that triggers the martensitic transformation, we use a THz-free electron laser (THz-FEL). Recently, a high-e ciency elastic wave generation at the surface of water has been reported using this THz source 21,22 , suggesting that generation of a mechanical force in t-ZrO 2 is possible.…”