Fig. 1: Holographic imaging of cavitation at the MID instrument.

a The FEL X-ray pulses are focused to nanometer spot size by the beryllium CRLs. A cuvette with water is placed behind the X-ray focus. The pump laser is focused by a lens and reflected by a subsequent plane mirror into the water to seed the bubble. The X-ray and the laser beam are antiparallel. The X-ray beam passes through a small hole in the laser mirror to the X-ray detector. The distance between X-ray focus and laser focus, i.e., the seeding point of cavitation, is z₀₁ = 144 mm and between X-ray focus and detector z₀₂ = 9578 mm. A high-speed optical camera observes the bubble formation perpendicular to the X-ray beam. A microphone at the cuvette’s wall registers the acoustic signal of cavitation events. b Timing scheme of the experiment. The pump laser excites a cavitation bubble at a time Δt prior to the FEL pulse. The optical high-speed camera acquires a series of images with the first frame synchronized to the pump laser pulse. The microphone signal of the acoustics is recorded (mic). c Image sequence of the optical high-speed camera. The first frame (left) shows the plasma spark. The following frames have time delays of 40 μs, 140 μs, and 160 μs (left to right) with respect to the first frame. d Empty-beam corrected X-ray holograms of cavitation events at different times Δt, indicated in the top left corner. The holograms show strong contrast at the inner interface (gas/shockwave) and at the outer interface (shockwave/equilibrium water). Scale bars: 50 μm (a, d), 500 μm (c).