[EN]: Random lasers are systems able to generate laser light above a certain pumping threshold thanks to the multiple scattering processes that can create enough ampli cation to compensate the losses. Although, unlike traditional lasers, they have no cavity they still present laser modes determined by the multiple scattering of the random dielectric structure. They have been studied since the 1990s in very diverse materials, and can present two different con gurations: they are composed by either a gain medium with added scatterers or a medium with scatterers which have gain. Among random lasers one category known as diffusive random lasers attracts special attention. Nevertheless, the understanding of some of their features remains a challenge. In this thesis we study the emission properties and modal dynamics of two different materials, a diureasil doped with Rhodamine B and neodymium doped crystal powders, and the dependences of the emission features on the experimental con guration and material properties such as concentration and grain size. The spatiotemporal dynamics and spatial coherence of the Rhodamine B doped di-ureasil under one and two photon pumping is analysed thanks to a spatial ltering method to allow for mode selection. A streak camera provides time and wavelength resolved images of single shot measurements of both the pump pulse and the sample emission. We also present a detailed study of the emission of several Nd3+ stoichiometric and low-doped powders and explore their laser slope, threshold energy, absorption and the spatially integrated pulse dynamics. Lastly, we explore two applications of the studied phenomena. On the one hand, we study the suitability of Nd3+ doped powder samples as NIR source for specklefree imaging and, on the other hand, the cooling of discrete regions by anti-Stokes processes of Nd3+ doped oxysul de powders.

[ES]: En esta tesis llevamos a cabo un estudio de las propiedades de la emisión de láseres aleatorios difusivos en materiales micro-nanoestructurados activados con colorantes orgánicos y en polvos dieléctricos cristalinos dopados con tierras raras. Para ello, estudiamos, por una parte, la dinámica resuelta en espacio y tiempo de los modos de la emisión de un láser aleatorio basado en un di-ureasil dopado con Rodamina B y molido, bajo bombeo a uno y dos fotones con un láser de picosegundos. El empleo de un sistema de filtrado espacial permite analizar la dinámica de modos únicos, ,las oscilaciones de relajación que presentan y revela su comportamiento estocástico tanto en la respuesta espectral como en la temporal. Además, se observa un alto grado de coherencia temporal en la emisión del sistema. Por otra parte, caracterizamos la emisión de distintos cristales molidos dopados con Nd3+ bombeados con un láser de nanosegundos y exploramos la relación entre el slope, la absorción, las longitudes de onda del bombeo y emisión y la energía umbral. Estos sistemas demuestran ser adecuados como fuente de luz infrarroja para técnicas de imagen, con la interesante característica de no producir speckle.

This thesis is the result of a four-year doctorate in the Escuela de Ingeniera de Bilbao of the Basque Country University (UPV/EHU) under the supervision of Prof. J. Fernandez and Prof. I. Iparraguirre and has been supported by a FPI grant of the MINECO (Spanish Government).

Peer reviewed