directing a pump light from one or more pump light sources each consisting of a high power diode array and its coupling system into a laser slab through prior cut-off slab corners of said laser slab without restriction to the incident angle or the polarization state of the pump light, wherein said laser slab is a convex polyhedron having one or more cut-off corners, which is formed by cutting one or more edges and vertexes of a rectangular parallelepiped, and includes an undoped circumambient portion and one or more doped central portions, wherein said undoped circumambient portion and said one or more doped central portions are diffusion bonded without gaps between them, said undoped circumambient portion has said corner faces and a plurality of lateral surfaces used as inner reflective surfaces, and all the plurality of lateral surfaces are planar;

propagating said pump light within said laser slab, wherein said pump light firstly pass said undoped circumambient portion, secondly pass said doped central portion, thirdly pass said undoped circumambient portion again, and fourthly take inner reflection at the plurality of lateral surfaces of said undoped circumambient portion, and by repeating these steps, achieve multi-pass absorption; and

substantially absorbing the pump light by the said doped central portion during propagating.