The sidewall angle (SWA) of a nanostructure exerts influence on the performance of the nanostructure and plays an important role in processing nano-structural chips. It is still a great challenge to determine steep SWAs from far field measurements especially when the SWAs are close to 90°. Here, we propose a far-field detection system to determine steep SWA of a cliff-shape step structure on a silicon substrate by combining a split detector with a scanning method. The far-field radiation field is asymmetric due to the scattering of the step structure, and further numerical analysis demonstrates the reliability of this far-field measurement method. In the simulations, two key variables, i.e. the polarization state and the focus position of the incident laser beam, are considered to explore their impacts. By scanning over the structure laterally and longitudinally with both TE and TM polarizations, polarization effects on the far-field occur. These effects show higher sensitivity to steep SWA variation for TM polarization as compared to TE. Furthermore, with a comprehensive longitudinal scanning analysis for the TM polarization case, a feasible focus interval can be optimized to retrieve the steep SWA. As the proposed method is fast, highly sensitive and easy to implement, it provides a powerful approach to investigate the scattering behavior of nanostructures.

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Improving the image quality of small particles is a classic problem and especially challenging when the distance between particles are below the optical diffraction limit. We propose a imaging system illuminated with radially polarized light combined with a suitable substrate that contains a thin dielectric layer to demonstrate that the imaging quality can be enhanced. The coupling between the evanescent wave produced in a designed thin dielectric layer, the small particles and the propagating wave forms a mechanism to transfer sub-wavelength information about the particles to the far field. The smallest distinguished distance reaches to 0.634λ, when the imaging system is composed of a high numerical aperture (NA=0.9) lens and the illumination wavelength λ = 632nm, beyond the diffraction limit 0.678λ. The lateral resolution can be further improved by combining the proposed structure with superresolution microscopy techniques.

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We report a novel method of focus determination with high sensitivity and submicrometre accuracy. The technique relies on the asymmetry in the scattered far field from a nanosphere located at the surface of interest. The out-of-focus displacement of the probing beam manifests itself in imbalance of the signal of the differential detector located at the far field. Up-down scanning of the focussed field renders an error S-curve with a linear region that is slightly bigger than the corresponding vectorial Rayleigh range. We experimentally show that the focus can be determined not only for a surface with high optical contrast, such as a silicon wafer, but also for a weakly reflecting surface, such as fused silica glass. Further, for the probing wavelength of 405 nm, three sizes of polystyrene latex spheres, namely 200, 100, and 50 nm in diameter, are tested. Higher sensitivity was obtained as the sphere diameter became smaller. However, due to the fact that the scattering cross-section decreases as the sixth power of the nanosphere diameter, we envision that further size reduction of the studied sphere would not contribute to a drastic improvement in sensitivity. We believe that the proposed method can find applications in bio/nano detection, micromachining, and optical disk applications.

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Lateral resolution enhancement is demonstrated in a confocal imaging system with amplitude-modulated radially polarized (RP) light at the wavelength Annular pupil fields and optimized amplitude distribution functions can be realized with a spatial light modulator. By comparing images obtained with full and amplitude modulated apertures of RP illuminations using a high numerical aperture (NA = 0.9), spatial resolution of has been achieved experimentally. This result agrees very well with theoretical simulation results and will be helpful in improving performance of the non-fluorescent imaging systems.

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The Rayleigh criterion explains the diffraction limit and provides guidance for improving the performance of an imaging system namely by decreasing the wavelength of the illumination and/or increasing the aperture (NA) of the objective lens. If the wavelength and NA are set, is it possible to improve the spatial resolution further? This question motivates the research work of this thesis. Polarization is an important property of light and it can not be ignored in a tightly focusing system. It is demonstrated both theoretically and experimentally that radially polarized light can produce a sharper focal spot in a high NA focusing system because of the tight longitudinal field component. Based on this, in this thesis, we start our investigation on the unique focusing properties of the radially polarized beam with the vectorial diffraction theory. We show that the amplitude of the focal field can be shaped by engineering the pupil field of the radially polarized beam. The shaped focal spot is smaller than the unmodulated one, which can be used to improve the resolution of optical systems. Here, we consider a confocal scanning imaging system, offering several advantages over conventional widefield microscopy. In the simulation, longitudinal electric dipoles are regarded as the objects to make the full use of the optimized longitudinal component. An experimental proof is also given, showing that higher spatial resolution can be achieved when the modulated radially polarized light is applied in the confocal imaging set-up as compared to the non-modulated case. Radially polarized light can be obtained with a liquid crystal based polarization convertor, starting with a linearly polarized beam. Amplitude modulation of the pupil such as the annular pupil field and the designed pupil field where the amplitude increases gradually with the radius can be realized with a spatial light modulator (SLM). The substrate is essential for supporting the sample to be imaged. Usually, the material of the substrate is glass. In the near field, when the object interacts with the light field, it may produce evanescent waves which decays very quickly and has little influence on the imaging. However, the evanescent wave carries higher spatial frequency than the propagating wave. A well designed substrate with a thin TiOኼ layer on top can enhance the evanescent wave in the near field. The enhanced field transfers to a propagating wave with the help of the object deposited on the substrate and it can be detected in the far field. The principle can be explained with a dipole model, and simulated using nanospheres. It is demonstrated that the designed structure helps to improve the imaging quality including contrast and resolution. In addition, such sample model can be combined with other imaging techniques, e.g. confocal scanning microscopy, widefield imaging system, etc. Besides amplitude and polarization, focal fields can also be shaped in phase. Unlike the specific radially or azimuthally polarized vector beam, the cylindrical vector beam is a more general form. The focusing properties and the spin-orbit interacitions of cylindrical vector vortex beams in high NA focusing systems are theoretically studied. An absorptive nanosphere can be trapped at the hot-spot of the focused field, even when the field has its axial symmetry broken. The analysis on the influence of parameters such as the initial phase of the vortex beam, the topological charge, or the size and the material of the trapping sphere on the interplay between spin and angular momentum may be helpful for optical trapping, particle transport and super-resolution. @en

Nonzero transverse energy flow, which describes phenomenon in which the energy flux of localized light propagates in a plane perpendicular to the optical axis, has attracted enormous interest recently due to its useful application in micromanipulation. We show that the appearance of transverse energy flow in the focal plane of an aplanatic high numerical aperture focusing system is possible. We demonstrate our approach by specially tailoring the input state of polarization. Calculations reveal that number of transverse energy flow rings is controllable and depend on azimuthal index of the input field, thereby giving rise to tunable manipulating locations in optical trapping.

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With dual two-dimensional Airy-like waveforms, we demonstrate the creation of highly confined electromagnetic fields in the transverse plane and circular or elliptical propagation trajectories in the longitudinal plane by using specially designed Pancharatnam-Berry (PB) phases. Applying the Richards and Wolf vectorial diffraction methods, the explicit expressions are obtained to calculate the strength vectors and energy flux of the three-dimensional electromagnetic fields. Calculations reveal that the nanointerferometric structures of such highly confined fields highly depend on the indexes γ₁ and γ₂ determining the PB phase, thereby enabling the engineering of highly confined fields with tunable size, spacing, and propagation trajectories.

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Optical angular momenta (AM) have attracted tremendous research interest in recent years. In this paper we theoretically investigate the electromagnetic field and angular momentum properties of tightly focused arbitrary cylindrical vortex vector (CVV) input beams. An absorptive particle is placed in focused CVV fields to analyze the optical torques. The spin-orbit motions of the particle can be predicted and controlled when the influences of different parameters, such as the topological charge, the polarization and the initial phases, are taken into account. These findings will be helpful in optical beam shaping, optical spin-orbit interaction and practical optical manipulation.@en

Rigorous vectorial focusing theory is used to study the imaging of small adjacent particles with a confocal laser scanning system. We consider radially polarized illumination with an optimized amplitude distribution and an annular lens to obtain a narrower distribution of the longitudinal component of the field in focus. A polarization convertor at the detector side is added to transform radial polarization to linear polarization in order to make the signal detectable with a single mode fiber.

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Scattering of light by a periodic array of metal-coated nanocylinders located on a dielectric slab is analyzed by using a semi-analytical method based on a recursive algorithm combined with the lattice sums technique. The resonance phenomena observed in the spectral responses of the scattered field are numerically investigated.

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