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 %.