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Free space optical networks have emerged as a viable technology for broadband wireless backbone networks. In this paper, we investigate the challenging problem of joint topology design and load balancing in FSO networks. We consider FSO link characteristics, cost constraints, traffic characteristics, traffic demand, and QoS requirements in the formulation, along with various objective functions including network-wide average load and delay. We apply the Reformulation-Linearization Technique (RLT) to obtain linear programming (LP) relaxations of the original complex problem, and then incorporate the LP relaxations into a branch-and-bound framework. The proposed algorithm can produce highly competitive solutions with performance guarantees in the form of bounded optimality gap. The RLT-based branch-and-bound algorithm is evaluated with extensive simulations and is shown to be highly suitable for jointly optimizing topology and load balancing in FSO networks.