## 3 Results
### Impact of Beam Translation Rate along the Surface of the Sample When Cutting in Water  
It was noticed that the rate at which the beam is scanned multiple times along the surface impacts the results as well, and a maximum is present at a specific scanning speed setting. This is illustrated in Figure 11. It is observed that the optimal conditions for cutting are from approximately 75 mm/s to 150 mm/s (for the scanning speed setting). It is our belief that at a specific scanning speed setting a kind of optimal transformation of the water layer to a water-vapor state takes place so that the coefficient of non-linear losses and n\({}_{2}\) are lower than in the case of water, although they are still significant enough that the flat-top-semi flat-top beam transformation is still possible. Such a case is to some extent visible when using the shadowgraphic setup and imaging the water and glass interface while the beam is being scanned. When scanning the beam at lower translation speeds (<50 mm/s), the water layer appears almost absent. For low scanning speeds, the pulse-to-pulse overlap is high, and as a portion of the energy is absorbed, the water layer is evaporated faster than it is replenished from the surrounding regions; in this case, the ablation process is similar to ablation in air and the process overall is less efficient as compared with other settings. The profile images of the grooves in this case strongly resemble the conventional V-shapes. Figure 11: Sample cutting speed vs. beam scanning speed along the surface of the sample. Figure 10: Beam intensity distribution dynamics vs. propagation distance in water when the initial energy of the beam is expressed as the ratio P/\({}_{\text{CR}}\). (**a**): 33 P/\({}_{\text{CR}}\), (**b**): 66 P/\({}_{\text{CR}}\), (**c**): 100 P/\({}_{\text{CR}}\). The point 0 \(\upmu\)m corresponds to the air-water interface. If the scanning speed is high (yellow region in Figure 11), the top portion of the water layer appears transformed, however, since the overlap is low in this case, each subsequent pulse needs to propagate though an unmodified layer of water, in which case it loses a significant portion of its energy until the photons arrive at the water-glass interface. Although this case is more efficient than the conventional case of ablation in air, as described in Section 3.1, apparently an even more efficient case is present when the water layer is fully transformed into a water-vapor state. This is represented by the green region in Figure 11. The volume through which the beam propagates appears dark with some reflections emerging from it. Most likely, this volume is a combination of water and vapor with a lower coefficient of non-linear losses (and different n\({}_{2}\)). However, experimental confirmation of that being the case is beyond the scope of this study for several reasons. With the use of light-probing techniques, only the integrated projection of the three-dimensional volume region is acquired, since the actual distribution of the water and vapor species are unknown and reconstruction of the object is not possible. The beam is constantly moving and probing is possible only in a narrow time window (since the probing equipment is stationary), which would make the experiments extend over a long period of time, as the samples would need to be relocated in order for ablation to occur at a new location every time. The region of interest produces the large scattering loss, therefore, sheet microscopy probing is not an option. It may be possible to image such a transient object (the transformed water and vapor region) using time-resolved tomography techniques (Optical coherence tomography OCT [53] may be a likely candidate), however this is a topic for future research.