Monday, July 1, 2013

High Resolution Nature Wallpaper

High Resolution Nature Wallpaper History


Super-resolution microscopy is a form of light microscopy. Due to the diffraction of light, the resolution of conventional light microscopy is limited as stated by Ernst Abbe in 1873.[1] A good approximation of the resolution attainable is the FWHM (full width at half-maximum) of the point spread function, and a precise widefield microscope with high numerical aperture and visible light usually reaches a resolution of ~250 nm.
Super-resolution techniques allow the capture of images with a higher resolution than the diffraction limit. They fall into two broad categories, "true" super-resolution techniques, which capture information contained in evanescent waves, and "functional" super-resolution techniques, which use clever experimental techniques and known limitations on the matter being imaged to reconstruct a super-resolution image.[2]
True subwavelength imaging techniques include those that utilize the Pendry Superlens and near field scanning optical microscopy, the 4Pi Microscope and structured illumination microscopy technologies like SIM and SMI. However, the majority of techniques of importance in biological imaging fall into the functional category.
There are two major groups of methods for functional super-resolution microscopy:
Deterministic super-resolution: The most commonly used emitters in biological microscopy, fluorophores, show a nonlinear response to excitation, and this nonlinear response can be exploited to enhance resolution. These methods include STED, GSD, RESOLFT and SSIM.
Stochastical super-resolution: The chemical complexity of many molecular light sources gives them a complex temporal behaviour, which can be used to make several close-by fluorophores emit light at separate times and thereby become resolvable in time. These methods include SOFI and all single-molecule localization methods (SMLM) such as SPDM, SPDMphymod, PALM, FPALM, STORM and dSTORM.
Contents  [hide] 
1 History
2 True super-resolution techniques
2.1 Near-field scanning optical microscope (NSOM)
2.2 Local enhancement / ANSOM / optical nano-antennas
2.3 4Pi
2.4 Structured illumination microscopy (SIM)
2.5 Spatially modulated illumination (SMI)
3 Deterministic functional techniques
3.1 Stimulated emission depletion (STED)
3.2 Ground state depletion (GSD)
3.3 Saturated structured illumination microscopy (SSIM)
4 Stochastic functional techniques
4.1 Localization microscopy
4.1.1 Localization microscopy SPDM SPDMphymod
4.1.2 Stochastic optical reconstruction microscopy (STORM), photoactivated localization microscopy (PALM) and fluorescence photoactivation localization microscopy (fPALM)
4.1.3 Label-free localization microscopy
4.1.4 Direct stochastical optical reconstruction microscopy (dSTORM)
4.1.5 Software for localization microscopy
4.2 Super-resolution optical fluctuation imaging (SOFI)
5 Combination of techniques
5.1 3D light microscopical nanosizing (LIMON) microscopy
6 See also
7 References
8 External links

In 1978, the first theoretical ideas had been developed to break this barrier using a 4Pi Microscope as a confocal laser scanning fluorescence microscope where the light is focused ideally from all sides to a common focus that is used to scan the object by 'point-by-point' excitation combined with 'point-by-point' detection.[3] Some of the following information was gathered (with permission) from a chemistry blog's review of sub-diffraction microscopy techniques Part I and Part II. For a review, see also reference.[4]
True super-resolution techniques[edit]

Near-field scanning optical microscope (NSOM)[edit]
Main article: Near-field scanning optical microscope
Near-field scanning is also called NSOM. Probably the most conceptual way to break the diffraction barrier is to use a light source and/or a detector that is itself nanometer in scale. Diffraction as we know it is truly a far-field effect: The light from an aperture is the Fourier transform of the aperture in the far-field.[5] But, in the near-field, all of this is not necessarily the case. Near-field scanning optical microscopy (NSOM) forces light through the tiny tip of a pulled fiber — and the aperture can be on the order of tens of nanometers.[6] When the tip is brought to nanometers away from a molecule, the resolution is limited not by diffraction but by the size of the tip aperture (because only that one molecule will see the light coming out of the tip). An image can be built by a raster scan of the tip over the surface to create an image.
The main down-side to NSOM is the limited number of photons you can force out a tiny tip, and the minuscule collection efficiency (if one is trying to collect fluorescence in the near-field). Other techniques such as ANSOM (see below) try to avoid this drawback.
Local enhancement / ANSOM / optical nano-antennas[edit]
Instead of forcing photons down a tiny tip, some techniques create a local bright spot in an otherwise diffraction-limited spot. ANSOM is apertureless NSOM: it uses a tip very close to a fluorophore to enhance the local electric field the fluorophore sees.[7] Basically, the ANSOM tip is like a lightning rod, which creates a hot spot of light.
Bowtie nanoantennas have been used to greatly and reproducibly enhance the electric field in the nanometer gap between the tips two gold triangles. Again, the point is to enhance a very small region of a diffraction-limited spot, thus improving the mismatch between light and nanoscale objects—and breaking the diffraction barrier.[8][9]
A 4Pi microscope is a laser scanning fluorescence microscope with an improved axial resolution. The typical value of 500–700 nm can be improved to 100–150 nm, which corresponds to an almost spherical focal spot with 5–7 times less volume than that of standard confocal microscopy.
The improvement in resolution is achieved by using two opposing objective lenses both of which focused to the same geometrical location. Also the difference in optical path length through each of the two objective lenses is carefully aligned to be minimal. By this, molecules residing in the common focal area of both objectives can be illuminated coherently from both sides and also the reflected or emitted light can be collected coherently, i.e. coherent superposition of emitted light on the detector is possible. The solid angle  that is used for illumination and detection is increased and approaches the ideal case. In this case the sample is illuminated and detected from all sides simultaneously.[10][11]
Up to now, the best quality in a 4Pi microscope was reached in conjunction with the STED principle.[12]

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