Second-order optical nonlinearities (chi((2))) were induced in commercial phosphate glasses (Schott, IOG-1) by the thermal poling technique. Maker fringe experiments were used to characterize the induced nonlinear regions. The results show that a near-anodic surface and a bulk chi((2)) are formed that are opposite in sign. The strength of the near-anodic surface chi((2)) is greater than that of the bulk. The overall magnitude of the induced chi((2)), as well as the surface to bulk ratio, increases as the applied voltage and poling temperature increase. A single-charge-carrier model and a nonblocking cathode describe the main features of the induced chi((2)) profile. (C) 2003 American Institute of Physics.