Abstract
When exposing small particles on a substrate to a light plane wave, the scattered optical near field is spatially modulated and highly complex. We show, for the particular case of dielectric microspheres, that it is possible to image these optical near-field distributions in a quantitative way. By placing a single microsphere on a thin film of the photosensitive phase change material Ge(2)Sb(5)Te(5) and exposing it to a single short laser pulse, the spatial intensity modulation of the near field is imprinted into the film as a pattern of different material phases. The resulting patterns are investigated by using optical as well as high-resolution scanning electron microscopy. Quantitative information on the local optical near field at each location is obtained by calibrating the material response to pulsed laser irradiation. We discuss the influence of polarization and angle of incidence of the laser beam as well as particle size on the field distribution. The experimental results are in good quantitative agreement with a model based on a rigorous solution of Maxwell's equations. Our results have potential application to near-field optical lithography and experimental determination of near fields in complex nanostructures.
Highlights
The ultimate performance of key technologies in photonics is limited by the diffraction of light, which can be overcome by using optical near fields (ONFs) [1]
The sample was mounted on a motorized translation stage and observed in-situ with a home-built microscope based on a long working distance microscope objective (20x, numerical aperture NA = 0.42) and a tube lens, equipped with a 12 bit charge-coupled device (CCD) camera and illuminated by a light emitting diode (LED)
We have demonstrated that the imprinting of optical near-fields originating from single colloidal particles in GST films enables the imaging of complex field distributions in full detail and even quantitative analysis of the so-produced features
Summary
The ultimate performance of key technologies in photonics is limited by the diffraction of light, which can be overcome by using optical near fields (ONFs) [1]. A straightforward method to study local optical field distributions of micro- and nanostructures is to imprint them onto the underlying substrate. The system is not disturbed by the scanning microscope tip and the actual imprinting of the optical field distribution is done during a very short time (i.e., with a single laser pulse) in contrast to typically time-consuming scanning processes.
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