Virtual image

Résumé

In optics, an image is defined as the collection of focus points of light rays coming from an object. A is the collection of focus points made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays. In other words, a virtual image is found by tracing real rays that emerge from an optical device (lens, mirror, or some combination) backward to perceived or apparent origins of ray divergences. In diagrams of optical systems, virtual rays (forming virtual images) are conventionally represented by dotted lines, to contrast with the solid lines of real rays. Because the rays never really converge, a virtual image cannot be projected onto a screen by putting it at the location of the virtual image. In contrast, a real image can be projected on the screen as it is formed by rays that converge on a real location. A real image can be projected onto a diffusely reflecting screen so people can see the image (the image on the screen play

Source officielle

https://en.wikipedia.org/wiki/Virtual_image

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Super-resolution optical microscopy using a glass microsphere nanoscope

Martinus Gijs, Hui Yang

A technique that allows direct optical imaging of nanostructures and determines quantitatively geometric nanofeatures beyond the classical diffraction limit by using high-refractive index glass microspheres is introduced. The glass microsphere is put on the nanostructure that is immersed in oil. When illuminated by conventional oil-immersion microscope objective, a magnified virtual image of the sample is projected by the microsphere and recorded by the same objective. The image reveals the sub-diffraction nanofeatures of the sample due to a highly focused focal spot generated by the microsphere, i.e. a so-called "photonic nanojet". Experimental results on nanostructures demonstrates a resolution of ~ λ/4 - λ/7, where λ is the illumination wavelength, by using a 60 μm glass microsphere and a normal wideband halogen lamp as illumination source.

2014

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Super-Resolution Imaging of a Dielectric Microsphere Is Governed by the Waist of Its Photonic Nanojet

Martinus Gijs, Gergely Huszka, Raphaël Etienne Jean Trouillon, Hui Yang

Dielectric microspheres with appropriate refractive index can image objects with super-resolution, that is, with a precision well beyond the classical diffraction limit. A microsphere is also known to generate upon illumination a photonic nanojet, which is a scattered beam of light with a high-intensity main lobe and very narrow waist. Here, we report a systematic study of the imaging of water immersed nanostructures by barium titanate glass microspheres of different size. A numerical study of the light propagation through a microsphere points out the light focusing capability of microspheres of different size and the waist of their photonic nanojet. The former correlates to the magnification factor of the virtual images obtained from linear test nanostructures, the biggest magnification being obtained with microspheres of similar to 6-7 mu m in size. Analyzing the light intensity distribution of microscopy images allows determining analytically the point spread function of the optical system and thereby quantifies its resolution. We find that the super-resolution imaging of a microsphere is dependent on the waist of its photonic nanojet, the best resolution being obtained with a 6 mu m empty set microsphere, which generates the nanojet with the minimum waist. This comparison allows elucidating the super-resolution imaging mechanism.

American Chemical Society2016

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We report dielectric microsphere array-based optical super-resolution microscopy. A dielectric microsphere that is placed on a sample is known to generate a virtual image with resolution better than the optical diffraction limit. However, a limitation of such type of super-resolution microscopy is the restricted field-of-view, essentially limited to the central area of the microsphere-generated image. We overcame this limitation by scanning a micro-fabricated array of ordered microspheres over the sample using a customized algorithm that moved step-by-step a motorized stage, meanwhile the microscope-mounted camera was taking pictures at every step. Finally, we stitched together the extracted central parts of the virtual images that showed super-resolution into a mosaic image. We demonstrated 130 nm lateral resolution (~λ/4) and 5 × 105 µm2 scanned surface area using a two by one array of barium titanate glass microspheres in oil-immersion environment. Our findings may serve as a basis for widespread applications of affordable optical super-resolution microscopy.

2018

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