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The numerical aperture with respect to a point P depends on the half-angle, ... The NA of a Gaussian laser beam is then related to its minimum spot size ...
The Gaussian function has a 1/e 2 diameter (2w as used in the text) about 1.7 times the FWHM.. At a position z along the beam (measured from the focus), the spot size parameter w is given by a hyperbolic relation: [1] = + (), where [1] = is called the Rayleigh range as further discussed below, and is the refractive index of the medium.
Memorial in Jena, Germany to Ernst Karl Abbe, who approximated the diffraction limit of a microscope as = , where d is the resolvable feature size, λ is the wavelength of light, n is the index of refraction of the medium being imaged in, and θ (depicted as α in the inscription) is the half-angle subtended by the optical objective lens (representing the numerical aperture).
where the numerical aperture A is equal to the aperture ... An alternative measure of the spot size is to ignore the relatively small outer rings of the Airy ...
Numerical aperture: 0.85 0.65 0.85 or 0.6 0.6 Storage capacity ... which combined with the smaller spot size presents a problem when the surface is scratched as data ...
The PSF is also a fundamental limit to the conventional focused imaging of a hole, [9] with the minimum printed size being in the range of 0.6-0.7 wavelength/NA, with NA being the numerical aperture of the imaging system.
In optical communications testing, overfill in both numerical aperture and mean diameter (core diameter or spot size) is usually required. In polygonal mirror scanners, an overfilled type is one which uses each mirror facet at least in one dimension completely.
According to this equation, minimum feature sizes can be decreased by decreasing the wavelength, and increasing the numerical aperture (to achieve a tighter focused beam and a smaller spot size). However, this design method runs into a competing constraint. In modern systems, the depth of focus is also a concern: