The background of this thesis is the study of new laser sources with high brigthness for the pumping of erbium doped fiber amplifiers (EDFA), particularly in the telecommunications area. At present EDFA are pumped at 980 nm by spatially monomode laser diodes delivering an continous-wave (cw) output power of about 300 mW on an 1 mM by 3 mM emitting area. More powerful laser diodes present a larger emitting area, typically 1 mM by 100 to 200 mM. The consequence is a degradation of the spatial beam quality in the plane parallel to the diode function. In this direction the beam is 10 to 20 times diffraction limited, which is a problem for applications that need a high power density on a small area (for example, the pumping of EDFA or the pumping of solid-state lasers). The challenge is to have a spatially monomode laser source with a cw output power of about 1 W at 980 nm. In this thesis we studied two solutions. The first one is to improve the spatial beam quality of laser diodes by an angular filtering of the beam. For that, we used an external cavity and the angular filtering was realized by a Bragg grating that we designed. The second solution is to use the highly multimode beam from a power laser diode to pump a laser crystal. Ytterbium doped crystals are interesting, since they may present an laser transition around 980 nm. The problem is that this transition is a real 3 level one. We demonstrated that with a good choice of the crystal host and of the pumping conditions, it is possible to realize an efficient cw laser emitting around 980 nm.
