Airy spot is a light spot formed at the focus due to diffraction when a point light source images through diffraction limit. There is a bright circular spot in the center, surrounded by a group of faint concentric annular stripes, and the central bright spot surrounded by the first dark ring is called Airy spot.

Airy spot is named after george biddell airy, a British astronomer. Because he gave the theoretical explanation of this phenomenon for the first time in the paper 1835.

Diffraction:

In classical physics, waves will bend and propagate in different degrees after passing through obstacles such as slits, holes or disks. If an obstacle is placed between the light source and the observation screen, bright areas and dark areas will appear on the observation screen, and the boundaries of these areas are not clear, which is a complex pattern of alternating light and dark.

This phenomenon is called diffraction, which may occur when waves encounter obstacles in the propagation path. In addition, similar effects will occur when light waves pass through a medium with uneven refractive index or sound waves pass through a medium with uneven acoustic impedance.

Under certain conditions, not only water waves and light waves can be diffracted by naked eyes, but also other types of electromagnetic waves (such as X-rays and radio waves) can be diffracted. Because the actual object at atomic scale has wave-like properties, it will also show diffraction phenomenon, and its properties can be studied through quantum mechanics.

Under appropriate conditions, any wave has inherent diffraction properties. However, in different cases, the degree of diffraction of waves is different. If there are many densely distributed pores on the obstacle, it will cause more complicated diffraction intensity distribution pattern. This is because different parts of the wave propagate to the observer's position in different paths, and the phenomenon of wave superposition appears.

The form of diffraction can also be used to describe the propagation of finite waves in free space (measured as waves of finite size). For example, the divergence of laser beam, the beam shape of radar antenna and the field of view of ultrasonic sensor can all be analyzed by diffraction equation.