An optically pumped semiconductor laser is assembled in an enclosure comprising a base, a first mounting frame attached to the base, a second mounting frame attached to the first mounting frame and a cover attached to the second mounting frame. The assembly base, frames, and cover forms an undivided enclosure, with the frames contributing to walls of the enclosure. Components of the laser are assembled sequentially on the base and the frames. The frames are irregular in height to permit flexibility in the mounting-height of components. This reduces the extent to which compactness of the enclosure is limited by any one component.