Mirrors for a deflection unit in a scanning system, scanning systems using such mirrors, and methods of manufacturing such mirrors are disclosed. In an embodiment, a mirror for a deflection unit in a laser system includes a sintered polycrystalline diamond body including a plurality of randomly oriented diamond grains defining a plurality of interstitial regions. At least a portion of the interstitial regions includes a material disposed interstitially therein. The mirror includes a reflective surface formed at least partially from the sintered polycrystalline diamond body or provided thereon. The reflective surface exhibits a surface roughness of less than about 50 nm Rrms.