High Accuracy Subwavelength Distance Measurements: A Variable-Angle Standing-Wave Total-Internal-Reflection Optical Microscope

We describe an extension of the total-internal-reflection microscopy technique that permits direct in-plane distance measurements with high accuracy (< 10 nm) over a wide range of separations. This high position accuracy arises from the creation of a standing evanescent wave and the ability to sweep the nodal positions (intensity minima of the standing wave) in a controlled manner via both the incident angle and the relative phase of the incoming laser beams. Some control over the vertical resolution is available through the ability to scan the incoming angle and with it the evanescent penetration depth.