Time-power monitoring technique was used for monitoring the thickness of optical films during ion beam sputter deposition. For Ta2O5, in the initial stage of coating, the growth rate increases with deposition time. While for SiO2, the rate increases first and then decreases. Both growth rates eventually stabilize when a proper ratio of atoms are sputtered from target materials. Finally, the mismatch of optical thickness and the inhomogeneity of film layers that affect substantially the optical performance of the samples were discussed. (c) 2005 Elsevier B.V. All rights reserved.