Working Principle Of Anti Reflective Film

Working principle of anti reflective film
Anti reflective film, also known as anti reflective film, is mainly used to reduce or eliminate the reflected light on the surface of optical lenses such as lenses, prisms, and plane mirrors. Its working principle is based on the interference and reflection of light. The following is a detailed introduction for you:

Principle of interference
Reflection and Interference Phenomena of Light
When light is irradiated onto the anti reflective film, a portion of the light will be reflected back on both sides of the film, and these two columns of reflected light will interfere. If the thickness of the film meets certain conditions, the two columns of reflected light waves will be coherent and destructive. For example, when the thickness of the film is appropriate, the distance difference between the reflected light on the two surfaces of the film is exactly equal to half a wavelength, thus canceling each other out. This greatly reduces the reflection loss of light and enhances the intensity of transmitted light.

The relationship between film thickness and wavelength
The thickness of the anti reflective film is usually one-quarter wavelength. In theory, an odd multiple of 0.5 wavelength optical path difference can weaken the interference of reflected light, but as the film thickness increases, the transmission will weaken. Therefore, 0.25 times the wavelength is generally chosen. Taking red light as an example, if the thickness of the film is equal to one fourth of the wavelength of red light in the anti reflection film, the red light reflected back on both sides of this film will interfere and cancel each other out. At this time, the beam of red light will all pass through the lens and no reflection will be seen in front of the lens.

Reflection Principle
The function of multi-layer thin films
Anti reflective films are generally composed of 3-4 layers of optical thin films arranged alternately, with each layer having a thickness not exceeding 1/4 of the wavelength, forming total reflection within a certain wavelength range, which can reduce reflectivity and increase transmittance. By stacking multiple such thin film layers in sequence, an anti reflective film is formed. It utilizes the reflection and interference between material layers with different transmittance to enhance transmission while reducing reflection.

Selection of materials and wavelengths
The thickness and refractive index of the thin film layer of the anti reflection film are determined based on the wavelength required for anti reflection. When light passes through the thin film layer of the anti reflection film, interference occurs when the thickness of the thin film layer is close to the wavelength of the light. According to the relationship between the wavelength of light and the thickness of the thin film layer, a portion of the light waves can be enhanced to pass through, thereby increasing the transmittance. Meanwhile, by selecting appropriate film thickness and refractive index, the reflectivity of light at specific wavelengths can be reduced, further improving the transmittance