X-ray imaging of laser-induced cavitation bubbles with femto-second FEL pulses: probing the early pressure distribution of the shockwave
The pressure distribution of shockwaves surrounding expanding cavitationbubbles is not accessible with optical methods shortly after bubble seeding.Within the first nanoseconds after seeding, the shockwave has propagated onlya few micrometers and has increased only to a cross section in the micrometerrange. The spatial resolution of optical methods sensitive to the density of thefluid is not sufficient to resolve these length scales.X-ray holography with single X-ray free-electron laser (XFEL) pulses has now enabled a quasi-instantaneous high resolution structural probe withquantitative contrast. The phase shift can be accessed by phase retrieval ofthe holographic intensity and is proportional to the electron density of the object. We present results on X-ray holography with single-XFEL pulses oflaser-induced cavitation bubbles. The quantitative contrast gives direct access to spatial and temporal mass density distribution of the shockwave, onlynanoseconds after seeding and in close proximity to the bubble nucleus. We calculate the pressure distribution of the shockwave from the density of the fluid.The experimental results are compared to numerical simulations.