The diameter of the hole on the surface of an object. Pore diameter refers to the shape and size of pores in porous solids.
In fact, the hole is extremely irregular, which is usually regarded as a circle and its radius is used to represent the size of the hole. The pore size distribution is usually related to the adsorption capacity of adsorbent and the activity of catalyst. The pore size distribution below 10nm can be determined by gas adsorption method, and the pore size distribution of some mesopores and macropores can be determined by mercury intrusion method.
The numerical aperture (NA) of an optical system is a dimensionless number, which is used to measure the angular range of light that can be collected by the system. The precise definition of numerical aperture is slightly different in different optical fields. In the field of optics, numerical aperture describes the cone angle of lens, which determines the light receiving ability and spatial resolution of lens. In the field of optical fiber, numerical aperture describes the cone angle of light when it enters and exits the optical fiber.
Numerical aperture is the main technical parameter of lens and condenser, and it is an important symbol to judge their performance (especially the objective lens) (that is, the ability to eliminate positional chromatic aberration, and the numerical aperture of Zeiss company represents the ability to eliminate positional chromatic aberration and magnification chromatic aberration). Its values are marked on the shell of the objective lens and condenser respectively.
The numerical aperture (NA) is the product of the sine value of the refractive index (N) of the medium between the lens and the detected object and the half aperture angle (2α). Expressed as follows: NA=n*sinα. Aperture angle, also called "mirror angle", is the angle formed by the object point on the optical axis of the lens and the effective diameter of the front lens of the objective lens. The larger the aperture angle, the greater the luminous flux entering the lens, which is directly proportional to the effective diameter of the lens and inversely proportional to the distance of the focus.
Technical parameters:
Numerical aperture is closely related to other technical parameters, which almost determines and affects other technical parameters. It is proportional to the resolution and magnification, and the focal depth is inversely proportional to the square of the numerical aperture. With the increase of NA value, the width of field of view and working distance will decrease accordingly.
In the field of laser physics, the definition of numerical aperture is slightly different. The laser beam diverges at a small angle during its propagation. Far from the narrowest point of the beam, the divergence of the beam is approximately linear with the propagation distance-equivalent to the beam forming a cone in the "far field".