Diffraction limit of light

There is no inherent sample size restriction, large or small, but is fixed by the optical components used in the instrument. The diffraction limit of light, roughly a few cubic micrometers depending on the numerical aperture of the optics used and the laser s wavelength, sets the lower bound.7 In a process application, the type of fiber optics used also affects sample volume examined. Macroscopic to microscopic samples can be measured with the appropriate selections of laser wavelength, laser power, and optics. 

To date, a number of chemically selective near-field imaging methods have been demonstrated. Near-field contrast mechanisms that rely on electronic spectroscopy (UV-visible absorption and fluorescence),204 vibrational spectroscopy (IR absorption and Raman spectroscopies), dielectric spectroscopy (microwave dispersion), and nonlinear spectroscopy (second harmonic generation) have all been demonstrated at length scales well below the diffraction limit of light. 

Dictated by the diffraction limit of light, the lateral resolution of a far-held optical microscope is dehned as the smallest distance between two features that can still be resolved in the image and is given by Rayleigh criterion as [5]... 

This chapter describes Raman spectroscopy with a high spatial resolution beyond the diffraction limit of light. 

Near-field optics is another promising way to achieve high-density optical memory. Since near-field techniques overcome the diffraction limit of light by the contribution of evanescent wave, it is possible to store a bit datum in a nanometric region. The nanometric resolution is achieved by the contribution of evanescent fields. 

The practice of using a beam of electrons to generate patterns on a surface is known as electron beam lithography. The primary advantage of this technique is that it is one of the ways to beat the diffraction limit of light and make features in the sub-micrometer regime. Beam widths may be on the order of nanometer as of the year 2005. This form of lithography... 

Total internal reflection fluorescence (TIRF) microscopy is one of the more complicated techniques for more advanced users of fluorescence microscopy techniques. In order to obtain fluorescent information about small features less than 0.5 pm, this technique uses decaying evanescent waves to probe a focal volume below the diffraction limit of light. 

Stimulated emission depletion (STED) microscopy is another microscopy approach to overcome the diffraction limitation of light microscopy by inhibiting fluorescence outside of the focal spot [9]. In this context, fluorescence is viewed as spontaneous light emission while stimulating emission via synchronized laser... 

Weiss S (2000) Shattering the diffraction limit of light a revolution in fluorescence microscopy Proc Natl Acad Sci 97 8747-8749... 

The spatial resolution of conventional optical microscopy is limited by the diffraction limit of light consequently, two objects that are close to each other cannot be resolved in the fluorescence image. The minimum resolvable distance. Ax, is given as follows ... 

Eor optical microscopy, the most significant advantage of TERS is its high spatial resolution beyond the diffraction limit of light An optical field is spatially confined into a region several tens of nanometers in size at the tip of the metalUc probe [55, 56], On the other hand, according to Abbe s theory, the minimum size A that can be resolved by a conventional optical microscope is given by [57]... 

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