Case 1: the spot size and wavelength of light irradiated on the grating remain unchanged.

Case 2: Change the parameters of incident light without changing the grating parameters.

Grating diffracts first, then the slit interferes, which is the same as Young's interference principle. When the sum of the amplitudes of all parts is equal to zero, it is a sufficient condition to produce dark lines, and its combined vibration is also equal to zero, which satisfies the interference cancellation and produces the phenomenon of leakage. When the position of the maximum bright stripe of grating diffraction coincides with the position of the dark stripe of single slit diffraction, a gap will appear.

Detailed description:

If the grating period d becomes smaller, the number n of grating lines covered by light spots will become larger. However, the grating slit width a is always smaller than d, so with the decrease of grating period d, the value of m_ vacancy will be larger and larger. At the same time, according to the grating equation, it can be deduced that the order m of the transmitted diffracted light is:

m = d/λ* sin(θ)？

λ is the wavelength of incident light, θ is the angle of diffracted light, and m is an integer. Then we can see that the smaller the d/lambda, the smaller the range of m.

Therefore, when m _ is missing >:m is established, there is no missing grade phenomenon. That is, when the grating period is close to or smaller than the wavelength of incident light, or when the slit width is much smaller than the size of incident light in the direction perpendicular to the grating line, no voltage drop phenomenon can be seen.