A device for emitting a laser beam comprises a cylindrical solid amplifier medium, having a fluorescence wavelength λ, delimited by a surface Σ connecting two faces and intended to be pumped through both the faces, or one of them, in order to become a gain medium. It comprises a cooling fluid of thermal conductivity Cr in contact with the amplifier medium over one of the faces, and an index matching liquid that absorbs or scatters the fluorescence wavelength, of thermal conductivity Ci