Ultra High Spatial And Temporal Resolution Using Scanning Near Field Optical Microscopy

Scanning near-field optical microscopy (SNOM) is a system that can image beyond the conventional diffraction limit. It does this by collecting the information contained within evanescent fields. This unique ability to image using evanescent fields also enables SNOM to directly measure the electric field distribution in waveguides, where light is guided by total internal reflection. When SNOM is used with a spectrally resolving detector, local temporal phenomena can be detected by analysing spectral interference in the spectra collected by the probe. This spectrally resolving configuration was used to directly measure inter-modal group velocity difference in a multimode ridge waveguide and, using the modes' spatial profiles to experimentally determine the mode amplitude coefficient ratio. Such an ability to provide measurements on the local dispersion characteristics and relative modal amplitudes of guided light establishes SNOM as a route for investigating the conversion of current single mode photonic devices into multimode devices. The spectrally resolving SNOM system was also used to investigate the sources of temporal delays created by a quasi disordered scattering sample, which was based on John H. Conway's pinwheel tiling. Whilst the measurements do not create a complete picture of the scattering phenomena in this work, suggestions for improvement are offered with the aim establishing spectrally resolving SNOM systems as tools for mapping localised temporal phenomena in disordered scattering systems.

This project elucidated and examined the unique science behind the spectral and temporal contrast of near field scanning optical microscopy, illuminated the technology this enabled, and considered the limits of simultaneous position, time and spectral resolution. Specifically, (1) High-resolution, quantitative measurements of excess carrier lifetime in silicon were acquired in a novel, all-optical technique. The contrast in the images was modeled and is of interest since the resolution is significantly shorter than the carrier diffusion length. (2) a Ti-sapphire laser has been constructed and modified to decrease pump power requirements so that measurements can be made before the carriers diffuse from under the probe. Novel electron-hole droplet effects are expected. (3) Spectroscopic nano-Raman images were acquired for the first time. The Raman data illustrated interesting manifestations of a near-field in comparisons with far-field spectroscopy. (4) The first and most thorough studies of the optical and thermal properties of near-field scanning optical microscope probes gave insights which led to the development of a new generation of high throughput probes. Other results reflect instrumentation advances: (5) A new constant linear motion system useful for NSOM or other probe microscope coarse approach. (6) A new, low cost force feedback system. (7) A nanometer-resolution, kHz bandwidth, millimeter range position sensor.

The near-field scanning optical microscope, or NSOM, proyides spatial resolution of surface features considerably smaller than the wavelength of the radiation used to image. We have focused on both the development and the use of the NSOM. In the former, we considered the confinement of optical fields to nanometric structures. We analyzed the delivery of light from the far-field to the near-field region in tapered optical fibers. Our analysis led to the design and development of near-field probes of that allow for the performance of relatively light-starved NSOM experiments. Using such probes, we have demonstrated a capability of using spectral contrast in near-field imaging. In studies of KTP, for example, we have performed nano-Raman spectroscopy samples, and have imaged sub-wavelength surfaces features using only Raman-scattered light. In ongoing research we have launced further efforts to improve probe design and have begun nano-Raman investigations Mercury Cadmium Telluride and semiconducting diamond.

For more than a century, microscopy has been a centerpiece of extraordinary discoveries in biology. Along the way, remarkable imaging tools have been developed allowing scientists to dissect the complexity of cellular processes at the nano length molecular scales. Nanoimaging: Methods and Protocols presents a diverse collection of microscopy techniques and methodologies that provides guidance to successfully image cellular molecular complexes at nanometer spatial resolution. The book's four parts cover: (1) light microscopy techniques with a special emphasis on methods that go beyond the classic diffraction-limited imaging; (2) electron microscopy techniques for high-resolution imaging of molecules, cells and tissues, in both two and three dimensions; (3) scanning probe microscopy techniques for imaging and probing macromolecular complexes and membrane surface topography; and (4) complementary techniques on correlative microscopy, soft x-ray tomography and secondary ion mass spectrometry imaging. Written in the successful format of the Methods in Molecular BiologyTM series, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step protocols, and notes on troubleshooting and avoiding known pitfalls. Authoritative and accessible, Nanoimaging: Methods and Protocols highlights many of the most exciting possibilities in microscopy for the investigation of biological structures at the nano length molecular scales.

Optical microscopes are widely used in many areas, such as microbiology, material science, and medical diagnosis. In traditional microscopic systems, the trade-off between the resolution and the imaging field of view (FOV) is a long-standing problem. For the conventional microscopy, a larger numerical aperture (NA) usually leads to a smaller FOV and a shorter depth-of-focus. To overcome this limitation, this thesis presents several novel imaging techniques from two aspects: innovations in whole slide imaging (WSI) systems, and developments of lensless on-chip ptychographic microscopy platforms. Firstly, we report a novel WSI platform based on color-multiplexed illumination and single-shot autofocusing. Compared to previous implementations, our scheme requires no focus map surveying, no secondary camera or additional optics, and allows for continuous sample motion in the dynamic focus tracking process. Secondly, we explore the use of deep convolution neural networks to predict the focal position in the WSI system without axial scanning. We show that the information from spatial, Fourier and autocorrelation domains substantially improves the performance and robustness of the autofocusing process. Thirdly, we report a novel lensless on-chip imaging platform for wide-field, high-resolution microscopy based on near-field blind ptychographic modulation. Fourthly, we report a resolution-enhanced parallel coded ptychography system achieving the highest NA and an imaging throughput orders of magnitude greater than previous demonstrations. Lastly, we develop an integrated ptychographic sensor for lensless cytometric analysis of microbial cultures over a large scale and with high spatiotemporal resolution. We also report a new temporal-similarity constraint to increase the temporal resolution of ptychographic reconstruction by 7-fold.

Near-field scanning optical microscopy (NSOM) is a powerful technique which allows deeply subwavelength imaging by placing a nanoscale aperture in close proximity to a sample where it can collect evanescent fields which contain information about subwavelength features. Additionally, by coupling out these evanescent fields, it has the ability to image light propagation within light-confining guided-wave structures. NSOM can be enhanced by integration into the signal arm of a heterodyne interferometer (H-NSOM), which allows imaging of both amplitude and phase at subwavelength resolution. In this dissertation we apply H-NSOM to characterize novel structures, and introduce a new technique for using H-NSOM in a liquid environment. First, we use the H-NSOM to characterize an asymetric mode converter, which uses a one-way wavevector created by a metallic grating. The asymmetric propagation is visualized directly, then verified by using Fourier analysis to examine the mode content of the waveguide fields. Next, we propose and implement a scheme for H-NSOM measurement of silicon integrated waveguides with liquid cladding. Fourier analysis is used to determine an effective index shift of .08 in the quasi-TM mode between air and water overcladdings. This technique is then succesfully applied to directly image long range surface plasmons for the first time. The liquid cladding enables preservation of the symmetric cladding environment required for long range plasmon propagation. We directly observe the field distribution of the single mode, and show that it matches well to simulations.

Biophysics is a rapidly-evolving interdisciplinary science that applies theories and methods of the physical sciences to questions of biology. Biophysics encompasses many disciplines, including physics, chemistry, mathematics, biology, biochemistry, medicine, pharmacology, physiology, and neuroscience, and it is essential that scientists working in these varied fields are able to understand each other's research. Comprehensive Biophysics, Nine Volume Set will help bridge that communication gap. Written by a team of researchers at the forefront of their respective fields, under the guidance of Chief Editor Edward Egelman, Comprehensive Biophysics, Nine Volume Set provides definitive introductions to a broad array of topics, uniting different areas of biophysics research - from the physical techniques for studying macromolecular structure to protein folding, muscle and molecular motors, cell biophysics, bioenergetics and more. The result is this comprehensive scientific resource - a valuable tool both for helping researchers come to grips quickly with material from related biophysics fields outside their areas of expertise, and for reinforcing their existing knowledge. Biophysical research today encompasses many areas of biology. These studies do not necessarily share a unique identifying factor. This work unites the different areas of research and allows users, regardless of their background, to navigate through the most essential concepts with ease, saving them time and vastly improving their understanding The field of biophysics counts several journals that are directly and indirectly concerned with the field. There is no reference work that encompasses the entire field and unites the different areas of research through deep foundational reviews. Comprehensive Biophysics fills this vacuum, being a definitive work on biophysics. It will help users apply context to the diverse journal literature offering, and aid them in identifying areas for further research Chief Editor Edward Egelman (E-I-C, Biophysical Journal) has assembled an impressive, world-class team of Volume Editors and Contributing Authors. Each chapter has been painstakingly reviewed and checked for consistent high quality. The result is an authoritative overview which ties the literature together and provides the user with a reliable background information and citation resource