Near Field Of Light Research Articles

Probing vectorial near field of light: imaging theory and design principles of nanoprobes.

Near-field microscopy is widely used for characterizing electromagnetic fields at nanoscale, where nanoprobes afford the opportunity to extract subwavelength optical quantities, including the amplitude, phase, polarization, chirality, etc. However, owing to the complexity of various nanoprobes, a general and intuitive theory is highly desired to assess the vectorial responses of nanoprobes and interpret the mechanism of the probe-field interaction. Here, we develop a general imaging theory based on the reciprocity of electromagnetism and multipole expansion analysis. The proposed theory closely resembles the multipolar Hamiltonian for light-matter interaction energy, revealing the coupling mechanism of the probe-field interaction. Based on this theory, we introduce a new paradigm for the design of functional nanoprobes by analyzing the reciprocal dipole moments, and establish effective design principles for the imaging of vectorial near fields. As application examples of the proposed theory, we numerically analyze the responses of two typical probes, a split-ring probe and a nanoparticle probe, which can quantitatively reproduce and well explain the experimental results of previously reported measurements of the optical magnetism and the transverse spin angular momentum. Our work provides a powerful tool for the design and analysis of new functional probes that may enable the probing of various physical quantities of the vectorial near field.

Characteristics of photonic nanojets from ordered microassemblies of dielectric spheres

Spatially localised light structures (photonic nanojets) formed in the near field of light scattering from an ordered ensemble of single-layer clusters of transparent glass microspheres have been theoretically studied. The main parameters of photonic nanojets (length, width, focal distance and intensity) are calculated based on numerical solution of Maxwell equations, and their behaviour under conditions of interference between neighbouring microparticles is analysed. The degree of manifestation of collective effects during the formation of a nanojet array is found to depend on the spatial structure of the ensemble of microspheres, their size and repetition period. It is found that in some cases, having chosen an appropriate configuration of a microsphere ensemble, one can improve significantly the characteristics of the photonic nanojets formed by this ensemble.

Near field of light diffracted by an ultrasonic wave, beyond the Raman–Nath diffraction regime

The near field of ultrasonically diffracted light is examined for a wide range of Raman-Nath (v) and Klein-Cook (Q) parameter values up to the region of total light rediffraction phenomenon occurrence to the zeroeth diffraction order. The behavior of the secondary interference plane position is studied, both theoretically and experimentally, for vari- ous Q and v values. In addition, the relationship is shown between dif- fracted light intensity modulation minima localization shift and rediffrac- tion phenomenon. A comparison is made of the results of the general Fresnel region theory, including the influence of complex light amplitudes over the diffracted light intensity distribution, with those obtained from Cook's simplified near-field description. The same, limited validity range of the latter theory is revealed. For all the experimental conditions con- sidered, quite good agreement is observed between experimental data obtained and the appropriate theoretical predictions. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)00507-3)

An ampere-like law for displacement vector field and near-field optical microscopy

We make up a novel and simple theory for near field and near-field optical microscopy (NOM). Our theory is composed of two parts. The first is a formulation to calculate the scattered near field of light by a small dielectric. We state that a wavenumber-vector-independent picture appears in the theory of the near field, and we find that this is expressed by an Ampere-like law for the displacement vector field. The second part is a formulation of field intensity for far field observation and near field observation from a unified point of view. We suggest a theoretical formula for the field intensity corresponding to the NOM image and demonstrate how to understand the relation between the near field and this image.

Plane-wave analysis of the near field of light diffracted by ultrasound.

Although the phenomenon of light diffraction by ultrasound has been studied very extensively during the last 40 years, almost all investigations were concentrated on the individual far field (Fraunhofer) diffraction orders. In the present paper, the basic theory is developed for studying the near field (Fresnel region) of light diffracted by an arbitrary plane ultrasonic wave and the fundamental periodicity properties are stated. The general plane-wave theory of Raman-Nath has been taken as a starting point. From the analysis, the near field of the diffracted light is seen to be highly sensitive to variations of the ultrasonic amplitude and this feature provides a useful technique for observing weak ultrasonic waves. In particular, for the specific case of Raman-Nath-type diffraction, a procedure is presented allowing the reconstruction of the time waveform of the ultrasonic wave from the diffracted light intensity signal.