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 μm in diameter, we measure spatial resolution due to refraction contrast of λ/4.3 at a wavelength of λ=10.7 μm. 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.