**5. Conclusions**

**Figure 16** illustrates the particle formation inside a cavitation bubble generated by laser-

The time shown is at the instant of the largest extent of the bubble. After irradiation of the target by the laser, primary particles are formed. Over time, these primary particles coagulate to form larger, secondary particles. While the secondary particles are trapped inside the cavitation bubble, some of the primary particles can escape from the inside of the cavitation bubble to the surrounding fluid. In other words, the interface of the cavitation bubble is not

Agglomeration occurs for the confined particles in the second cavitation bubble, which forms after the first bubble has collapsed. Additionally, upon the collapse of the second bubble, a jet

From this one can see that the lifetime of the cavitation bubble, the pressures and temperatures reached inside the cavitation bubble, and the conditions of the surrounding fluid all influence

In another study, to monitor the formation of nanoparticles in situ, a multipurpose timeresolved spectrometer was developed, that allows following the formation of nanoparticles over several timescales [41]. The spectrometer consists of three different parts, one that can be used for following the nanoparticle formation by time-resolved absorption spectroscopy in the wavelength range of 350 − 850 nm and on timescales of nanoseconds to milliseconds in the time following the laser pulse. The second part consists of an absorption spectrometer that allows following the nanoparticle formation on timescales of seconds to hours between 220 and 900 nm, and the third component, which dynamic light scattering for tracking nanopar-

In addition to the characterization methods mentioned above, it is worth noting that there are still other methods that can be used for investigating the effects of PLA. One is by numerical simulation. The mechanisms of PLA have been investigated for vacuum or ambient gas

In this section, we give a brief overview of alternative applications of PLA for the characterization of exotic environments, for example, at deep sea levels, or the exploration of the surface

Spectroscopy techniques are increasingly becoming important in deep-sea exploration and geochemical assessment of solids and liquids, as they enable rapid, in-situ measurements. Laser-induced breakdown spectroscopy (LIBS) has also been used for the deep-sea exploration [17], that is, the examination of soil, or of water composition. The setup consists of a laser

an impenetrable wall or membrane, but instead can be crossed by particles.

238 Applications of Laser Ablation - Thin Film Deposition, Nanomaterial Synthesis and Surface Modification

ticles with sizes ranging from 10 nm to 10, over timescales of seconds to hours.

of confined material is ejected perpendicularly to the target surface.

the nucleation and growth of nanoparticles.

*3.2.1. Other characterization methods*

conditions [42].

**4. Other applications**

of extraterrestrial bodies—planets and comets.

irradiation of a target surface placed inside a liquid [39].

Pulsed laser ablation in high-density fluids is a versatile technique that enables the functionalization and fabrication of metallic, semiconductor, and organic nanomaterials, which cannot not be obtained easily by other methods. Moreover, pulsed laser ablation in high-density media can also be used as an analysis technique in extreme environments such as in deep sea environments, to gain information about elemental composition at such positions. There are still many phenomena that are not well-understood, especially with respect to the plasma formation, cavitation bubble dynamics, and the nanomaterials growth in the cavitation bubble.

As has been hopefully explained in the present review, the use of spectroscopy techniques in particular SAXS and XRR—can aid in gaining a better understanding of growth processes of nanoparticles obtained by PAL of targets in liquids. To the best of our knowledge, so far these techniques have not been extended to the high pressure regimes yet, but we think that the same techniques could also be adapted to high pressure and SCF media, in order to further optimize the size, morphology, and composition of nanoparticles obtained by PLA.

We hope that the present review could give a short perspective on the current state in this field of research and that it can aid in contributing to the further expansion of this research.
