Extreme light interaction with matter—II. Dense systems, absorption physics, and fast-electron transport [Invited]

This review presents a perspective on the growth of high peak power, ultrashort laser pulses, and efforts to harness them to generate ultra-large intensities of light that can create extreme states of high temperature and high density in matter. It begins by exploring the evolution of the laser sources over the past few decades and traces their interaction across different forms of matter from single atoms to solids, highlighting the common as well as unique features of the physical processes involved. The subject is intrinsically linked to cutting edge technological developments and we present some of these examples: particle acceleration, bright electromagnetic radiation, and material particle sources with their applications in imaging, material manipulation, and medical therapies. Given the nature of this review, the South Asian context is woven into the narrative, presenting our perspectives on the past and plans for the future. This review is divided into four parts. The title of each part indicates its core content but we have attempted to preserve the thematic coherence and cross discussions among the parts. We urge the reader to read them together to get a complete perspective of the article. Having examined the generation of extreme light and its interaction with single atoms, single molecules, underdense gaseous plasmas, and finite gaseous clusters in Part I, we move up the density ladder and look at liquids and solids in this part. Later, we discuss the optics of plasmas and physics of absorption and fast-electron transport in dense, hot matter.