All Questions
10
questions
1
vote
2
answers
110
views
How do scientists focus high energy electromagnetic waves onto a target?
For visible light, we are able to use mirrors to focus on what we want.
However, gamma rays' wavelengths are too short and can't see solid objects.
So how do scientists focus high-energy ...
- 625
3
votes
1
answer
744
views
Why is photocathode damaged by excessive photocurrent due to exposure to intense light?
Many books including the book (Hamamatsu, "Photomultiplier Tubes", link to PDF) says that a photocathode of a photomultiplier tube is damaged by intense light.
Do not expose to strong light....
- 175
0
votes
0
answers
276
views
Why do we believe local gauge invariance (that tells us photons are exactly massless)? [duplicate]
There are experimental upper limits on the photon's mass, but they are finite. I heard that the reason we know that photons have exactly zero rest mass (and thus travel exactly at the universal ...
- 101
2
votes
1
answer
1k
views
What is zero-order transmission spectrum?
In the paper The extraordinary optical transmission through subwavelength hole arrays by T. W. Ebbesen it is shown at particular wavelength there is a peak observed in zero order transmission spectrum....
- 39
0
votes
1
answer
260
views
about the Pound-Rebka experiment and the answer to a second year undergrad student' s question 7 months ago [closed]
The answer tells us about a specific subtraction of the doppler shift so as to obtain the net gravitational redsift. Can anyone explain all this thing about that subtraction?
0
votes
1
answer
647
views
Coulomb law and photons
When we consider process like
$e^- e^- \to e^- e^-$
in QED, we see that from exchanges of one photon (tree-level diagrams) one can obtain Coulomb's law, while loop-diagrams give quantum corrections ...
- 546
8
votes
5
answers
3k
views
How do they find the energy of a photon?
Is the actual energy of a photon ever measured? How is it done?
I read that a photon is usually identified by diffraction, that means its wavelength is measured, is that right? In this way we ...
user104372
3
votes
1
answer
522
views
Help me understand Pound and Rebka's experiment
I am a second year undergrad physics student and up until now have done some classical mechanics and some electrodynamics. For some reason I have always been really interested in light. A couple of ...
user98025
3
votes
2
answers
3k
views
Electromagnetic Momentum
My book says : The fact that electromagnetic radiation of energy carried momentum was known from classical theory and from the experiments of Nichols and Hull in 1903. This relation is also consistent ...
user24082
11
votes
1
answer
994
views
How the inverse square law in electrodynamics is related to photon mass?
I have read somewhere that one of the tests of the inverse square law is to assume nonzero mass for photon and then, by finding a maximum limit for it , determine a maximum possible error in $\frac{1}...
- 728