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Register a new userImage formation properties and inverse imaging problem in aperture based scanning near field optical microscopy
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Aperture based scanning near field optical microscopes are important instruments to study light at the nanoscale and to understand the optical functionality of photonic nanostructures. In general, a detected image is affected by both, the transverse electric and magnetic field components of light. The discrimination of the individual field components is challenging, as these four field components are contained within two signals in the case of a polarization-resolved measurement. Here, we develop a methodology to solve the inverse imaging problem and to retrieve the vectorial field components from polarization- and phase-resolved measurements. Our methodology relies on the discussion of the image formation process in aperture based scanning near field optical microscopes. On this basis, we are also able to explain how the relative contributions of the electric and magnetic field components within detected images depend on the probe geometry, its material composition, and the illumination wavelength. This allows to design probes that are dominantly sensitive either to the electric or magnetic field components of light.
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The finite-difference time-domain (FDTD) method is employed to solve the three dimensional Maxwell equation for the situation of near-field microscopy using a sub-wavelength aperture. Experimental result on unexpected high spatial resolution is reproduced by our computer simulation.
A theory is presented to describe the heat-flux radiated in near-field regime by a set of interacting nanoemitters held at different temperatures in vacuum or above a solid surface. We show that this thermal energy can be focused and even amplified in spots that are much smaller than those obtained with a single thermal source. We also demonstrate the possibility to locally pump heat using specific geometrical configurations. These many body effects pave the way to a multi-tip near-field scanning thermal microscopy which could find broad applications in the fields of nanoscale thermal management, heat-assisted data recording, nanoscale thermal imaging, heat capacity measurements and infrared spectroscopy of nano-objects.
Near-field scanning optical microscopy has been an indispensable tool for designing, characterizing and understanding the functionalities of diverse nanoscale photonic devices. As the advances in fabrication technology have driven the devices smaller and smaller, the demand has grown steadily for improving its resolving power, which is determined mainly by the size of the probe attached to the scanner. The use of a smaller probe has been a straightforward approach to increase the resolving power, but it cannot be made arbitrarily small in practice due to the steep reduction of the collection efficiency. Here, we develop a method to enhance the resolving power of near-field imaging beyond the limit set by the physical size of the probe aperture. The main working principle is to unveil high-order near-field eigenmodes invisible with conventional near-field microscopy. The destructive interference of near-field waves is induced in these high-order eigenmodes by the locally varying phases, which can reveal subaperture-scale fine structural details. To extract these eigenmodes, we construct a self-interference near-field microscopy system and measure a fully phase-referenced far- to near-field transmission matrix (FNTM) composed of near-field amplitude and phase maps recorded for various angles of far-field illumination. By the singular value decomposition of the measured FNTM, we could extract the antisymmetric mode, quadrupole mode, and other higher-order modes hidden under the lowest-order symmetric mode. This enables us to resolve double and triple nano-slots whose gap size (50 nm) is three times smaller than the diameter of the probe aperture (150 nm). The subaperture near-field mode mapping by the FTNM can be potentially combined with various existing near-field imaging modalities and promote their ability to interrogate local near-field optical waves of nanoscale devices.
We develop a theory to study apertureless scanning near-field optical microscopy which takes into account retardation, higher multipoles of the tip, and the multiple scattering between the tip and the surface. We focus on metallic systems and discuss the implication of the formation of tip-induced surface plasmon modes in the tip-surface system. We discuss the effects associated with the shift in energy of those modes as a function of the tip-surface distance. Both the local field and the scattering cross section are enhanced when the tip approaches the surface, but there is no general correspondence between the two enhancements.
We introduce a point-like scanning single-photon source that operates at room temperature and offers an exceptional photostability (no blinking, no bleaching). This is obtained by grafting in a controlled way a diamond nanocrystal (size around 20 nm) with single nitrogen-vacancy color-center occupancy at the apex of an optical probe. As an application, we image metallic nanostructures in the near-field, thereby achieving a near-field scanning single-photon microscopy working at room temperature on the long term. Our work may be of importance to various emerging fields of nanoscience where an accurate positioning of a quantum emitter is required such as for example quantum plasmonics.
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