A zig-zag laser has the ability to generate a high power beam while effectively removing heat without degrading the beam quality. The laser has a series of gaps interposed between the thin slabs, the gain medium, and between the thin slabs and the quartz windows to receive coolant and cool the cell assembly. The coolant flows transversely relative to the path of the laser and the flow of the coolant is in the opposite direction on each side of the thin slab to minimize the temperature gradient. The gaps in conjunction with the inner channel portions in the secondary manifold flow the coolant through the cell assembly in a laminar manner therein not degrading the laser beam quality. A transparent quartz/quartz interface between the secondary manifold and the cell assembly allow the fluorescence to move away from the cell assembly and minimizes heat in the cell assembly.