How to achieve optical invisibility? How to achieve geometric optical stealth?

Just imagine that achieving the effect of complete "transparency" such as glass does not make much sense in actual combat use, transparency will still be found when it is already very close, and transparency does not have much effect when it is far away, such as a distance of more than 20 meters, but it is enough to conceal, and it is enough to add color and conceal to achieve the same tone as the background environment. To give a simple and crude example, hang a display on a red wall, how to make this display blend into this wall, display red, the closer to the color of this wall, the better. Of course, this is just to say that the significance of adding color to the background is hidden, and in real combat application, it is not very good to use a method similar to this active light display.

It should be better to deflect similar fine particles to achieve inverted colors to show different colors, isn't it said that some butterfly wings themselves do not have pigment, the color is because the scale reflection is different, the problem is how to make the clothes (or cloaks) on the body correctly recognize the surrounding environment. Some of the other answers are obscured in a way that is similar to light bypass, but does not involve the problem of environmental recognition. <>

Geometric optics is an important practical sub-discipline in optics that studies the propagation and imaging laws of light based on light. In geometric optics, the point of matter that makes up an object is regarded as a geometric point, and the beam of light emitted by it is regarded as a collection of countless geometric rays, and the direction of the light represents the direction of propagation of light energy. Under this assumption, according to the law of light propagation, it is very convenient and practical to study the process of objects being imaged by lenses or other optical elements, as well as to design the optical system of optical instruments.

In geometric optics, the point of matter that makes up an object is regarded as a geometric point, and the beam of light emitted by it is regarded as a collection of countless geometric rays, and the direction of the light represents the direction of propagation of light energy.

The above concept of light is contrary to the fluctuating nature of light. Because this kind of geometric ray is impossible to exist from the point of view of energy or from the point of view of the diffraction of light. Therefore, geometrical optics is only an approximation of wave optics, which is the limit case when the wavelength of the light wave is very small.

With this approximation, geometrical optics can solve optical technical problems in optical instruments in a simple way without involving the physical nature of light.

The propagation of light follows these basic laws:

The law of linear propagation of light. Light travels in a straight line in a homogeneous medium. Phenomena such as eclipse, shadow and pinhole imaging testify to this fact, and many optical surveys, such as geodesy, are based on this.

The law of independent propagation of light. When two beams of light meet on the way of propagation, they do not interfere with each other and continue to propagate according to their respective paths. And when two beams of light converge at the same point, the light energy at that point is simply added.

The law of reflection and the law of refraction. When light travels through a smooth interface between two different media, one part is reflected and the other part is refracted. The direction of propagation of reflected and refracted rays is determined by the laws of reflection and refraction, respectively.

The principle of optical path reversibility: no matter how many times a ray of light is reflected and refracted from a point, if it encounters an interface reflection at right angles to the beam at the end, the beam will return to the starting point accurately.

Based on the above basic laws of light propagation, the propagation path of light in an optical system can be calculated. This computational process, known as ray tracing, is a necessary part of the design of an optical system.

I hope I can help you with your doubts.