Infrared reflection and transmission measurements are used to study (111)‐ and (100)‐oriented Ge samples which were implanted with sufficient fluences to produce a continuous amorphous layer. Two optical states of amorphous Ge are identified: (i) as‐implanted, amorphous state which has an infrared refractive index about 8% larger than that for single crystal Ge,nc=0.92nI; (ii) thermally stabilized amorphous state with an intermediate refractive index,nII=(0.963±0.002)nI. A shift of the fundamental absorption edge to higher energy occurs with the transition from the as‐implanted to the thermally stabilized, amorphous Ge state, but no change in the density is observed for the transition. Annealing at about 300 °C for 2 h produces the thermally stabilized state. Annealing for longer time or at higher temperatures causes measurable epitaxial regrowth. The regrowth rates and activation energies for both orientations are also determined and compared with values measured previously by another method. With the regrowth rate ∝e−Ea/kT,Ea=2.0 eV for both orientations and the regrowth rates at 350 °C are 46 A˚/min for (100) orientation and 4.0 A˚/min for (111) orientation, respectively.