na[數值孔徑]

Numerical Aperture 數值孔徑。 NA表征了光纖收集光的能力。光纖的數值孔徑越大，其集光能力越強。

Inoptics, the numerical aperture( NA) of an optical system is adimensionless numberthat characterizes the range of angles over which the system can accept or emit light. By incorporatingindex of refractionin its definition, NA has the property that it is constant for a beam as it goes from one material to another provided there is nooptical powerat the interface. The exact definition of the term varies slightly between different areas of optics. Numerical aperture is commonly used inmicroscopyto describe the acceptance cone of anobjective(and hence its light-gathering ability andresolution), and infiber optics, in which it describes the range of angles within which light that is incident on the fiber will be transmitted along it.