The Photoelectric Effect, Photon Duality, and The Double-Slit Experiment

[uby]

Hi everyone,

Thanks in advance for any insights you might be able to lead me to.

The photoelectric effect is a well known phenomenon where an incident photon of some energy can stimulate the emission of an electron when absorbed, so long as the energy of the photon can promote an electron beyond the fermi level to the vacuum level of the material.

Photons can also be regarded as waves, having an energy that is spread out over a statistical area until it interacts with a particle. In the double-slit experiment, photons (as well as other massive particles) have been shown to diffract and show interference patterns on a detector screen when going through a double slit. The famous result of the disappearance of this interference pattern when trying to observe which slit the photon travels through is something I've always admired.

Coming back to the photoelectric effect, have any experiments been done to show a similar phenomenon in trying to "observe" where electrons are emitted and thus where photons are being absorbed? The motivating thought behind this is that if the photon acts as a wave prior to interaction with anything, and suddenly behaves as a discrete particle once it interacts with an electron in the material, it should be possible to detect the location of this interaction. Would this alter the photoelectric effect, since it too is reliant on diffraction? I realize the processes are not exactly parallel, but I would like to think that a similar phenomenon could be seen and, possibly, put to use for real-world applications.

 

[uby]

Sorry, can this be moved to the Quantum forum? Not sure how it got here! Thanks

 

[dx]

Even when the photons interfere with each other in the slit experiment, they still arrive at the screen as photons, i.e. discrete packets of energy. That is the only thing that matters in the explanation for the photoelectric effect. Whether they were observed or not before the interaction with the electron, and whether the motion before the interaction was wave like or particle like doesn't matter because the exchange of energy with the electrons is still in packets.

 

[uby]

thanks for your reply dx. but I'm not sure I'm satisfied with the explanation.

in the double slit experiment, sending a single photon through the slit will still cause interference with itself. it's position on the detector (averaged over many photons) CHANGES with the process of observation.

could the same effect also occur with the photoelectric effect? ie - observation changes the spatial distribution of interaction between the energy packet and an electron?

 

[dx]

Sure. If you replace the screen in the double slit experiment with a metallic surface, then the places where the electrons are emitted from are just the places where the photons hit the material.

 

[uby]

thanks again dx. to be sure i understand then: if no act of observation takes place, the photoemission of electrons from the conducting surface would occur much like the scattering through the double slit - ie, the spatial orientation of electrons striking a detector would form an interference pattern. however, if an act of observation would occur, the spatial orientation of photoemitted electrons would appear like that of a determined path-of-flight average.

this would seem like a useful effect: changing the behavior of a material based upon observation. for example, in a solar cell that employs the photoelectric effect to generate electricity, the performance of the collector could be enhanced if the spatial distribution of electrons could be controlled.