Ultraviolet optical near-fields of microspheres imprinted in phase change films

We report an experimental method for directly imaging optical near-fields of dielectric microspheres upon illumination with ultraviolet nanosecond laser pulses. The intensity distribution is imprinted in chalcogenide films leaving behind a characteristic fingerprint with features below 200 nm in size, which we read out with high-resolution field emission scanning electron microscopy. The experimental results are well matched by a rigorous solution of Maxwell's equations. Compared to previous works using infrared femtosecond laser pulses, the use of ultraviolet nanosecond pulses is identified to be superior in terms of minimum recordable features size and surface roughness of the imprint.