Advancements of laser technologies and material science have revolutionized the ability to manipulate matter through irradiation with ultrafast light pulses. This progress enables not only the study of out-of-equilibrium dynamics but also allows for the selective control of material properties. On a fundamental level, the investigation of ultrafast dynamics reveals intricate details about the destruction and reformation of equilibrium phases, offering deeper insights into the interactions and correlations governing complex materials. Dissecting these contributions helps unravel the mechanisms driving emergent exotic phases in condensed matter.
Crucially, out-of-equilibriumphenomena open a route to explore the free energy landscape of materials, often presenting numerous local minima, some of which exhibit long lifetimes. Light irradiation thus provides a unique tool for accessing and stabilizing these metastable states, which can play a pivotal role in material control. Correlated matter, due to the close proximity in energy between different phases, presents an ideal system for manipulating the ground state and inducing exotic phases using light pulses. As a result, they stand out as a class of materials with the potential to drive next-generation technologies, from zero-loss current systems to ultrafast, energy-efficient switches. Their diverse and exotic phase diagrams, arising from a complex interplay of interactions and correlations,make them particularly promising for these advanced applications.

In this dissertation, I investigate and characterize of metastable states in correlated matter, probing their electronic signatures using time- and angle-resolved photoemission spectroscopy (trARPES). Beyond demonstrating their presence, I delve into the ultrafast dynamics of their origin, and the insights they provide into the microscopic properties of materials.

The thesis begins by detailing the experimental method, starting with the fundamental principles of ARPES and extending them into the time domain. Three case studies follow, investigating high-temperature superconductors (SC) (Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10), as well as the charge density wave (CDW) material TaTe2. Additionally, the final chapter, presents the development of a new trARPES beamline extending the technique into the vacuum ultraviolet (VUV) regime.