Large field, ultra-high numerical aperture (NA) lithography is desired in semiconductor manufacturing. We report progress in developing a scanning evanescent wave lithography (s-EWL) imaging head with a two-stage gap control system including a DC noise canceling air bearing, which houses an AC noise-canceling piezoelectric actuator. Various design aspects of the system, including gap detection, prism design, optical alignment, software integration, feedback actuation, and a scanning scheme have been developed to ensure sub-100-nm gap control. Experimental results have shown successful gap gauging with a gap noise root-mean-square (RMS) of 1.38 nm in static gap control, and 4.64 nm in linear scanning gap control. Integrating the prototype imaging head into a two-beam interferometer platform has demonstrated dynamic stepping imaging using fused silica and sapphire prisms, with potential NA values up to 1.85 (26-nm half-pitch). These results achieved with s-EWL provide a possible route to extend optical lithography to 16-nm generations and beyond when combined with double patterning techniques.