Fig. 1. A typical SEM image of the target.

Fig. 2. Experimental setup: Imaging system with one objective (Obj1) inside the vacuum chamber, and a second objective (Obj2) outside of the chamber, imaging the target on a CCD camera with magnification 16. The main laser pulse is split at beam splitter BS1 into two beams: A first beam that propagates to M3 and focuses with an off-axis parabolic mirror to interact with the target. A second delayed beam, that acts as a strobe and merges on the optical line of the imaging system at BS2. This delayed beam consists of white light with wavelength broaden by supercontinuum and delayed by 7 ns from the main beam.

Fig. 3. Typical images of the snow micro-structure (a) illuminated by LED, (b) illuminated by gating strobe and (c) illuminated by the strobe with image processing to normalize light intensity.

Fig. 4. Transections of the strobe images for different fluences and at different times relatively to the laser–snow interaction. (a) Laser fluence of $1~\text{J}/\text{cm}^{2}$, (b) fluence of $0.45~\text{J}/\text{cm}^{2}$ and (c) fluence of $0.35~\text{J}/\text{cm}^{2}$. (1) At few minutes before the interaction, (2) 7 ns after the interaction and (3) long after the interaction (few minutes).

Fig. 5. Strobe images of the snow micro-structures at different laser fluences and at different times according to laser–snow interaction. Laser at (a) 1, (b) 0.45 and (c) $0.35~\text{J}/\text{cm}^{2}$. (1) Strobe image before the interaction, (2) an image 7 ns after the interaction and (3) long after the interaction (few minutes).