# numerical aperture (NA)

The numerical aperture (NA) is a parameter for the concentration of light rays in optical systems. It determines the luminous intensity and resolving power of lenses. By definition, the numerical aperture indicates the bundle limit, which refers to the limiting rays. It is a dimensionless value that results from the sine of half the propagation angle of the limiting wavelength and also from the difference of the refractive indices of different materials.

- In optical transmission technology with optical waveguides, the numerical aperture is a measure of the light power coupled into optical waveguides. It depends on the coupling angle at which the light from a light source is fed into the optical waveguide. The larger the numerical aperture of an optical fiber, the more light can be coupled into the fiber. fibers The angle of incidence, also known as the acceptance angle, is in the limit range to the critical angle. The numerical aperture is determined by the sine of the acceptance angle and has a particular effect when two optical fib ers are joined, since inhomogeneities and different material densities can occur at these joints. Typical values for a step fiber are 0.2 to 0.3. For single mode fibers, the numerical aperture is 0.1.
- For compact discs( CD), DVDs and Blu-ray discs, the numerical aperture is important for the light scattering on the layer and, together with the wavelength, determines the optical resolution with which the laser beam scans the pits and lands. For compact discs, the numerical aperture is 0.45 and the distance between tracks is 1.6 µm. For DVDs, the spacing has been reduced to 0.74 µm and the numerical aperture 0.6, increased. For Ultra Density Optical( UDO), the NA value is 0.7, and for Blu-ray Disc and Professional Disc for Data( PDD), it is as high as 0.85.
- Inchip manufacturing, the numerical aperture (NA) supports the bundling of the light beam in the imaging optics of lithographic systems. The numerical aperture is used directly in EUV lithography systems as the EUV-NA technique to generate a light beam that is as sharply focused as possible.