*2.1. Material*

The choice of the polymers was based on a few criteria in order for them to be able to deliver good results when used for LSP; namely, good optical transmission to the laser wavelength at high laser intensity, and the capability to generate sufficient pressures. Two polymers fulfilling these conditions were chosen for use as confining materials for the study. The first one was an acrylate-based tape with a thickness of 1 mm . The second one was a cross-linked PDMS with a thickness of 2 mm. Both can be defined as pressure-sensitive adhesives [13], allowing an easy bonding and debonding of the confining material to the target.

For pressure determination, the targets chosen were pure aluminum foils 99.00% from Goodfellows company (AL000645, Coraopolis, PA, USA) with a thickness of 1 mm. Aluminum is a material of choice for its well-defined properties. The thickness was chosen as a way to separate the first peak from the velocity profile from the second peak caused by the shock wave going back and forth inside the material. To ensure contact between the polymer and the aluminum target, every potential bubble was pushed away by applying low pressure on the adhesive. For the water-confined regime, a water droplet was apposed on the surface of the aluminum target. For each confinement and each laser intensity used, three samples were tested to minimize potential error and ensure reproducibility of the results.
