The discussion centers on the interaction of polarized photons with polarization filters, specifically addressing energy absorption and polarization conservation. When a polarized photon is absorbed by a filter, its energy is transferred to the filter, resulting in a change from light energy to heat energy. The original polarization direction of the photon is not conserved; instead, it is altered based on the filter's orientation. The conversation highlights that while angular momentum is conserved, there is no law mandating the conservation of polarization in this context.
PREREQUISITESPhysicists, optical engineers, and students of quantum mechanics seeking to deepen their understanding of photon interactions with materials and the principles governing energy and polarization conservation.
One can take a polarized light beam, pass it through a polarized filter at a 45 degree angle and then through a second filter at a further 45 degree angle. The beam emerging from the second filter is now polarized 90 degrees different from the original (with reduced intensity by a factor of 2 if I recall correctly). So no, I would say that polarization is not conserved.entropy1 said:If a (polarized) photon is absorbed by a polarization filter, does its energy go into the filter?
I am wondering if that is the case to obey conservation laws.
And if it passes, is its original polarisation direction somehow conserved?
It occurred to me that, in quantum mechanics, a photon passing a polarisation filter can be viewed as in superposition of being passed and blocked. The polarisation-components of the passed part and the blocked part add up to the original polarisation (vector). So if we view the photon as being in superposition, polarisation would perhaps be conserved?jbriggs444 said:One can take a polarized light beam, pass it through a polarized filter at a 45 degree angle and then through a second filter at a further 45 degree angle. The beam emerging from the second filter is now polarized 90 degrees different from the original (with reduced intensity by a factor of 2 if I recall correctly). So no, I would say that polarization is not conserved.
That's not correct. A polarising filter is macroscopic, so it acts like a measurement device. If the photon goes through, then it is polarised in the direction set by the polariser.entropy1 said:It occurred to me that, in quantum mechanics, a photon passing a polarisation filter can be viewed as in superposition of being passed and blocked.
Yes. That's generally true when light is absorbed.entropy1 said:If a (polarized) photon is absorbed by a polarization filter, does its energy go into the filter?
Because there is no law that says that polarization should be conserved.entropy1 said:To generate entangled electrons, I believe that one can use radioactive elements that decay into other particles, in case of which if there result two electrons with spin, the spin must be conserved because the decaying particle was spin-neutral, so that the electrons have necessarily opposite spins. But if spin is conserved, why then not generally polarisation of photons?
The probability amplitudes of the photon's polarization direction in the filter's basis add up to the original polarization direction of the photon. If we take an ensemble of identically liniarly polarized photons, on average the polarization direction is conserved, right? (if we take blocked photons' polarization direction as perpendicular to passing ones)DrClaude said:Because there is no law that says that polarization should be conserved.
I don't understand. If you have bunch of photons with the same linear polarization and a linear polarizer at an angle with respect to the photon polarization, then you get as output photons that have a different linear polarization. As the blocked photons no longer exist, I don't see how you can say that polarization is conserved.entropy1 said:If we take an ensemble of identically liniarly polarized photons, on average the polarization direction is conserved, right? (if we take blocked photons' polarization direction as perpendicular to passing ones)
I can't see that the model involving blocking photons works. If you treat it as a wave / field phenomenon then the polariser just selects the appropriate components of the fields. There will always be a 'photon - based' argument for explaining any phenomenon but it would not be easy. Imo, your "bunch of photons" only have reality when they are created or detected. They can also be there when the wave interacts with the polariser but I am not sure what your 'blocking' idea actually means. If it were as simple as that, none would be passed at all if the polariser were not perfectly aligned.DrClaude said:As the blocked photons no longer exist, I don't see how you can say that polarization is conserved.