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Due to Snell's law, the numerical aperture remains the same: NA = n 1 sin θ 1 = n 2 sin θ 2. In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light.
Efforts to improve resolution by increasing the numerical aperture have led to the use of immersion lithography. As further improvements in resolution through wavelength reduction or increases in numerical aperture have become either technically challenging or economically unfeasible, much attention has been paid to reducing the k1-factor.
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).
All optical microscopes are diffraction-limited because of the wave nature of light. Current research focuses on techniques to go beyond this limit known as the Rayleigh criterion . The use of SIL can achieve spatial resolution better than the diffraction limit in air, for both far-field imaging [ 3 ] [ 4 ] and near-field imaging.
It is NA that determines optical resolution, in combination with the NA of the objective. Different condensers vary in their maximum and minimum numerical aperture, and the numerical aperture of a single condenser varies depending on the diameter setting of the condenser aperture. In order for the maximum numerical aperture (and therefore ...
A fixed collimator produces an image of the entrance aperture in which either a mirror (for imaging) or a grating can be positioned. Three camera optics with numerical apertures of 1.8, 3.75 and 30 provide image scales of 0.25, 0.12, and 0.015 arcsec/detector element for wide field, seeing-limited and diffraction-limited observations.
The refractive index of the index-matching material is higher than air allowing the objective lens to have a larger numerical aperture (greater than 1) so that the light is transmitted from the specimen to the outer face of the objective lens with minimal refraction. Numerical apertures as high as 1.6 can be achieved. [26]
Ball lenses are often used in fiber optics. Due to their short focal lengths and the subsequently small waist diameters they produce in a laser beam, they are ideally suited to focus nearly all of the light from a laser into an optical fiber core. The numerical apertures of the fiber and lens need to match. The fiber can usually be placed in ...