An additive manufacturing apparatus includes a platform, a dispenser to dispense layers of feed material on the platform, and a fusing system to direct an energy beam to fuse at least a portion of the outermost layer of feed material. The fusing system includes an energy source to emit the energy beam, a deformable mirror to receive the energy beam and reflect the energy beam, wherein a shape of the deformable mirror defines at least in part an intensity profile of the energy beam on the outermost layer of feed material, an actuator coupled to the deformable mirror, and a controller coupled to the actuator and configured to cause the actuator to deform the shape of the deformable mirror to adjust the intensity profile of the energy beam on the outermost layer of feed material in accordance to a desired profile.