Fig. 1. Schematic diagram of the combining system

Fig. 2. Schematic diagram of the 3.5 kW narrow linewidth fiber laser

Fig. 3. Design spectrum of high steepness beam split films

Fig. 4. Schematic diagram of the optical damage threshold test of coatings

Fig. 5. Temperature variation on surface of the coatings and observations results

Fig. 6. Output laser spectrum

Fig. 7. Output laser spot image and beam quality factor

Fig. 8. Variation of combined output power and combination efficiency