An interferometric-spatial-phase imaging (ISPI) system includes an alignment mechanism for obtaining continuous six-axis control of a scanning probe tip with respect to a coordinate system attached to a substrate. A gap detection mechanism measures tip height above a substrate and controls tip approach toward the substrate of one or more tips, as well as measures tip deflection during surface contact of the one or more tips. A plurality of complementary marks is provided for attachment to the one or more tips. A plurality of grating marks is provided to backdiffract a reflected beam from a flexible cantilever to detect high-frequency tip deflection in a compact configuration of a light source and a light detector.