**1. Introduction**

Laser-based methods have opened new possibilities for materials treatment and processing, chemical synthesis, and analysis. Pulsed laser deposition (PLD) has been widely used for the

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

fabrication of thin films (metallic, oxide, and complex heterostructures) and has become a mainstay for realizing high-quality thin films of different compositions [1].

Pulsed laser ablation (PLA) in liquids, which consists in the irradiation of a solid target placed inside liquids, has enabled the functionalization and fabrication of a wide range of nanomaterials. The main advantage of PLA is that it enables the fabrication of nanoparticles that cannot be obtained easily by other methods. Moreover, PLA realized in high-density media—highpressure gases, liquids, and supercritical fluids—has opened up new possibilities for controlling nanomaterials fabrication by PLA and has also lead to the discovery of new phenomena related to plasma-fluid interactions.

In the context of this chapter, we define high-density media as gases, liquids, or supercritical fluids at and above atmospheric pressures, that is, at pressures 0.1 MPa and densities *ρ*≳ 1 kg m-3. While there have already been extensive reviews on PLA in liquids and their applications for nanomaterials processing [2, 3] including high-density media [4], the main aim of the present chapter is to present the main differences between PLA in atmospheric pressure liquids and PLA in high-density media—high-pressure gases, pressurized liquids, and supercritical fluids—and to point out possible advantages of using PLA in such media, both for fundamental research and applications in materials science and processing.

The chapter is structured as follows: The first part (section 2) gives a brief overview on the phenomena related to the formation of PLA plasmas in dense media. We introduce the techniques used for generating plasmas by PLA in high-density media, and the fundamental phenomena encountered under such conditions. This part is also devoted to the description of the experimental instrumentation and analysis techniques. In the third part (section 3) gives an overview of the use of pulsed laser ablation to nanomaterials' synthesis and the characterization of nanoparticle growth processes using X-ray scattering techniques. Finally, in the last two parts (sections 4 and 5), we present briefly other possible applications of PLA in highdensity media and close the chapter with a short conclusion.

As mentioned above, while PLA in liquids or in atmospheric pressure gases has been investigated extensively, PLA in high-pressure/high-density media has not yet received as much attention, but we hope that the present review can help researchers gain an overview on this field.
