Refraction contrast imaging with a scanning microlens

We demonstrate subwavelength spatial resolution with a scanning microlens operating in collection mode with a large-area detector. Optical contrast is created by refraction of off-axis light rays at angles larger than the maximum collection angle. With a microfabricated silicon microlens 10 mum in diameter, we measure spatial resolution due to refraction contrast of lambda /4.3 at a wavelength of lambda =10.7 mum. A model based on ray tracing is developed to explain our result, and we show that lens diameter and index of refraction limit resolution for large emission and collection angles. (C) 2001 American Institute of Physics.