Anti-reflection coating and FULL reflection coatings

[fisico30]

Hello Forum,

to obtain good anti-reflection at one specific wavelength, a layer of the right index of refraction is deposited on a certain surface. The layer thickness must be d=lambda/4...
This achieves better transmission. If we used multiple layers we would get even better transmission.

What if we wanted to obtain the opposite effect, full reflection at a specific wavelength lambda? How wide would the layer need to be? Simply d=lambda/2?

Thanks
fisico30

 

[Meir Achuz]

The reflection cannot be made larger than it is with no interface.
That is, the best interface for maximum reflection is none.

 

[fisico30]

Hello Meir,

i just found the following: http://www.lamdapacific.com/lamda_admin/Lamda_Edit/UploadFile/2011222112937198.pdf

It seems that a certain stack of dielectrics can actually improve the reflection...

 

[AlexLAV]

The reflection cannot be made larger than it is with no interface.
That is, the best interface for maximum reflection is none.

May be I don't understand something, but if natural reflectivity of the surface is less than 100 %, you probably can use some cover with the reflectivity higher than that of the surface. With respect to multilayer dielectric mirror, typical reflection coeficient of so called high-reflectivity (HR) mirrors which are used in laser engineering is more than 99.8 % (I've met mirrors with 99.99 %, though at 45 deg of incidence). The layers of a HR mirror usually are deposited on a glass substrate, with typical Fresnel reflectivity of about 4 %.

 

[sardar]

I would like to clarify the concept of anti-reflection coatings and FULL reflection coatings. Anti-reflection coatings are designed to minimize the reflection of light at a specific wavelength by depositing a layer with the right index of refraction on a surface. This layer must have a thickness of d=lambda/4 to achieve optimal transmission. However, it is important to note that this is a simplified explanation and the actual thickness may vary depending on the materials and design of the coating.

On the other hand, FULL reflection coatings are used to achieve maximum reflection at a specific wavelength. In this case, the layer thickness would need to be d=lambda/2 to achieve this effect. However, it is important to consider that the thickness alone is not the only factor that determines the reflectivity of the coating. The materials used and the design of the coating also play a crucial role.

Furthermore, it is worth mentioning that the concept of full reflection is not always achievable in practice. In most cases, there will still be some level of reflection due to imperfections or limitations in the coating materials and design. Therefore, it is important to carefully consider the specific requirements and limitations when designing and using FULL reflection coatings.

In summary, anti-reflection coatings and FULL reflection coatings are two different approaches used to control the reflection of light at a specific wavelength. While the thickness of the coating plays a significant role, it is not the only factor to consider. As with any scientific concept, it is important to carefully consider all aspects and limitations when working with these coatings. Thank you for the interesting discussion.