Does attenuation affect subsequent interference?

[Swamp Thing]

Consider a 95% / 5% beam splitter. The 95% output is attenuated in a lossy medium until its intensity is equal to the 5% output.
If we now get these two beams to interfere, would the visibility be as good as the usual 50% / 50% case, or would there be some kind of added randomness that would reduce the coherence of the attenuated beam?

In other words, does the absorbing medium affect the phase of those photons that happen to survive absorption, in a "noisy" way? (Assume, however, that the photon energy is far greater than the thermal noise in the absorber).

 

[pixel]

Did you mean to say that the 95% output is attenuated to the 10% output, since you are asking about a 50/50 case?

To your question, if the medium introduces scattering, e.g. due to the presence of pigments, then the path length in the medium might be increased enough compared to the coherence length of the light that the visibility of the fringes could be reduced to some degree. For absorption without scattering, I would think there'd be no significant reduction but I'll be interested in other replies.

 

[Swamp Thing]

Thanks, pixel. I changed the 10% to a 5% -- it was a mistake.

 

[tech99]

Consider a 95% / 5% beam splitter. The 95% output is attenuated in a lossy medium until its intensity is equal to the 5% output.
If we now get these two beams to interfere, would the visibility be as good as the usual 50% / 50% case, or would there be some kind of added randomness that would reduce the coherence of the attenuated beam?

In other words, does the absorbing medium affect the phase of those photons that happen to survive absorption, in a "noisy" way? (Assume, however, that the photon energy is far greater than the thermal noise in the absorber).

If the light power is small enough, then of course the result will see photon noise but the phase relations and diffraction pattern are not altered.

 

[Swamp Thing]

Thanks!