Optical light transmission through a coating

[0kensai0]

If I was to measure the transmission of light through a coated piece of glass(with a coating designed to scatter light). Do I expect the optical transmission to be different if the light is incident upon the coated side compared to if the light is incident on the uncoated side and exits through the coated side??

Our resident spectroscoper said I should expect the same transmission, but we're unsure as to why (since we're a bunch of chemists with limited physics background)

Can anyone shed some light on this matter.

thanks beforehand

 

[Oscar6330]

I do not know the answer to your problem but I am sure that you can analyze it in simulation software such as lighttools. You can see the difference if coating is changed, or materials are changed or the shape. One way ahead is optimization using this software.

 

[Andy Resnick]

That's an interesting question. Have you measured any difference?

The reason it's interesting is because a similar phenomenon occurs in imaging through turbulence- satellites looking down at the Earth (with the scattering surface far away from the scope, and close to the object) can image well, while earth-bound telescopes looking up (through the nearby scattering medium, at the distant object) have problems. The same phenomenon can occur with fogged shower doors.

However, imaging is different than simple transmission. My suspicion is that the transmission will be very similar, unless the coating is highly scattering- enough to place a significant fraction of the incident light into the total internal reflection regime at the glass-air interface.

 

[Manchot]

I guess it depends more on the specifics of what you're talking about. If you're just concerned about relative spectral transmission (i.e., the shape of the spectrum in wavelength space), it will be more or less the same, especially if the coating is thick compared to the wavelength. But if you're concerned about the shape and direction of the field, or the absolute power, that's not necessarily the case. For example, if your "coating" was a beamsplitter oriented 45 degrees from the surface, it one direction it would send half the light propagating to the left, while the other would send half the light propagating to the right.