A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

비만아 부모의 돌봄 경험: q 방법론

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Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

Quantitative phase imaging (QPI) has emerged as a valuable method for investigating cells and tissues. QPI operates on unlabelled specimens and, as such, is complementary to established fluorescence microscopy, exhibiting lower phototoxicity and no photobleaching. As the images represent quantitative maps of optical path length delays introduced by the specimen, QPI provides an objective measure of morphology and dynamics, free of variability due to contrast agents. Owing to the tremendous progress witnessed especially in the past 10–15 years, a number of technologies have become sufficiently reliable and translated to biomedical laboratories. Commercialization efforts are under way and, as a result, the QPI field is now transitioning from a technology-development-driven to an application-focused field. In this Review, we aim to provide a critical and objective overview of this dynamic research field by presenting the scientific context, main principles of operation and current biomedical applications. Over the past 10–15 years, quantitative phase imaging has moved from a research-driven to an application-focused field. This Review presents the main principles of operation and representative basic and clinical science applications.

Quantitative phase imaging in biomedicine

Proceedings of the National Academy of Sciences

The size of the dark focal spot directly determines the resolution and stability of stimulated emission depletion (STED) microscopy. This paper investigates the relationship between the size of the dark focal spot and the polarization of the input light beam. The types of fundamental polarization are discussed, their effects on the dark focal spot are compared and the optimized mode for each kind of polarization is proposed. The results of the analysis provide the theoretical basis and reference for designing a STED system.

https://iopscience.iop.org/article/10.1088/2040-8978/12/11/115707/pdf

Effects of polarization on the de-excitation dark focal spot in STED microscopy

We demonstrate that a sharper focal spot area can be generated (0147λ2) by using an azimuthally polarized beam propagating through a vortex 0–2π phase plate than for radial polarization (017λ2) or for linear polarization (026λ2) under the same condition Further research illustrates that such optimistic results can still be expected when condition limitations are liberalized This will facilitate new approaches to get superresolution in confocal systems

Phase encoding for sharper focus of the azimuthally polarized beam.

We experimentally demonstrated that the microsphere can discern the details of the object whose sizes are below the conventional diffractive limit and such super-resolution capability can be reinforced if semi-immersing the corresponding microspheres in liquid droplet, producing a sharper contrast and a comparatively smaller magnification factor. The microsphere is considered as a channel that connects the near-field evanescent wave and the transmission one in far field. A conjecture based on this is proposed to explain the mechanism of super-resolution and the corresponding phenomenon.

Microsphere based microscope with optical super-resolution capability

We propose a novel physical mechanism for breaking the diffraction barrier in the far field. Termed fluorescence emission difference microscopy (FED), our approach is based on the intensity difference between two differently acquired images. When fluorescence saturation is applied, the resolving ability of FED can be further enhanced. A detailed theoretical analysis and a series of simulation tests are performed. The validity of FED in practical use is demonstrated by experiments on fluorescent nanoparticles and biological cells in which a spatial resolution of <λ/4 is achieved. Featuring the potential to realize a high imaging speed, this approach may be widely applied in nanoscale investigations.

/pdf/breaking-the-diffraction-barrier-using-fluorescence-emission-wkc81e5rtz.pdf

Breaking the Diffraction Barrier Using Fluorescence Emission Difference Microscopy

The resolution of conventional optical equipment is always restricted by the diffraction limit, and improving on this was previously considered improbable. Optical super-resolution imaging, which has recently experienced rapid growth and attracted increasing global interest, will result in applications in many domains, benefiting fields such as biology, medicine and material research. This review discusses the contributions of different researchers who identified the diffractive barrier and attempted to realize optical super-resolution. This is followed by a personal viewpoint of the development of optical nanoscopy in recent decades and the road towards the next generation of optical nanoscopy. Researchers in China have reviewed techniques for imaging at resolutions beyond the diffraction limit of light. Xiang Hao and co-workers from Zhejiang University in China describe how superlenses made from thin silver films and hyperlenses incorporating meta-materials can capture near-field evanescent waves that provide fine and rich spatial information about an object. Alternative approaches include placing transparent microspheres onto the object or scanning a microscale optical fiber across it. The role of popular fluorophore-based schemes such as STED, STORM and PALM, which achieve super-resolution imaging by employing the controlled switching of fluorescence in space and time, is also described. Finally, the authors comment on the emergence of approaches such as the HIRES lens, which uses light scattering to achieve enhanced resolution.

/pdf/from-microscopy-to-nanoscopy-via-visible-light-4pc30b0m1h.pdf

Cuifang Kuang

Papers

Effects of polarization on the de-excitation dark focal spot in STED microscopy

Phase encoding for sharper focus of the azimuthally polarized beam.

Microsphere based microscope with optical super-resolution capability

Breaking the Diffraction Barrier Using Fluorescence Emission Difference Microscopy

From microscopy to nanoscopy via visible light