Abstract: A laser comprising a laser cavity (13) having reflectors at each end of an optical path, a first layer of gain material (15) and a second layer of a second material (14, 16) disposed along the optical path, wherein the first and second layer are directly optically contacted to one another at associated faces. Also, a laser comprising a laser cavity having a layer of gain material (15), and second and third crystals (14,16) having anisotropic refractive indices disposed along an optical path, the laser being oscillatory in a preferred mode having a particular orientation of polarization, the second crystal (16) being oriented with respect to the path to cause no appreciable net depolarisation of the preferred mode, and the third crystal (14) being arranged such that the preferred mode is transmittable therethrough with minimal refraction.