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Energy transfer during photon interaction 
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#1
Nov812, 08:37 PM

P: 915

Let's consider a machzehnder apparatus
The picture is below: http://en.wikipedia.org/wiki/File:Ma...rferometer.png 1. When the photon encounters (and emerges from) a halfsilvered mirror does it loose any energy? The photon does change phase when it moves through a half silvered mirror, however does it loose energy? 2. Does a photon loose energy when its reflected of a full silvered mirror? 3. Does the photon loose any energy if one of the paths is blocked? (and its still detected at detector 1 or 2) 


#2
Nov812, 10:56 PM

P: 101

A photon off a silver mirror energy reduction is negligible in this setup. Energy loss results in longer wavelength light. Such processes are referred to as inelastic scattering, Raman scattering, or the overused term "nonlinear process".
The effect of the mirror partial reflection and transmission. 


#3
Nov812, 11:25 PM

P: 915

now to the last question, i.e.: if one of the arms/paths of the machzehnder is blocked and the photon happens to NOT take that path..... is there any change in the energy/wavelength of the photon? 


#4
Nov912, 09:32 AM

P: 101

Energy transfer during photon interaction
nope.



#5
Nov912, 10:12 AM

P: 130

Be careful when you talk about the "phase of a photon"  if you mean the phase of the electrical field, this is not welldefined (the expectation value of the electrical field of a single photon is always zero). If you want a welldefined phase, you need a coherent mixture of states with different photon numbers (see Haroche's Nobel prize).



#6
Nov912, 10:59 AM

P: 915

i don't fully understand the concept of quanta. Is it that: Quanta is the smallest unit of physical entity, however can increments less than a quanta be added? 


#7
Nov912, 11:30 AM

P: 101

(Take my comments with a grain of salt, as I tend to focus primarily on experiments. )
The conventional understanding is that the energy reduction or addition cannot be in increments less than a quanta. I find it convenient to delude myself by just accepting the wave interpretation, but allowing for discrete wave amplitudes. 


#8
Nov1112, 01:59 PM

P: 915




#9
Nov1112, 03:08 PM

Mentor
P: 16,111




#10
Nov1212, 07:53 AM

P: 101

San K. I think I see what your problem is. You know momentum is being transferred when a photon reflects off a surface, e.g. 'a sail'. From the imparted 'momentum' to the "sail", one can calculate the 'energy' transferred from the photon to the "sail ". Resulting in lower photon energy. You're asking if there is a limit to how small this energy reduction can be?
I want to say, 'no', but I'm not sure. However, this phenomena is exploited for a pretty clever technique called "doppler radar". 


#11
Nov1212, 09:34 AM

P: 915

I think QM would say that the energy reduction cannot be smaller than a quantum (whatever a quantum means in this context/system) on a separate, but similar, note  for example would the (difference in energy of) photons from the say EM/vibgyor spectrum then be in multiples of quanta? 


#12
Nov1212, 10:15 AM

P: 101

EM/vibgyor spectrum: If your system was in an infinite well, yes, they would be quantized. As the size of the well increases, the difference between energy levels would get smaller and smaller.
The word quantized is a word we (including me) are guilty of throwing around too casually. Unfortunately, the real answer to your questions lies in tediously slogging through the DiracSchrodinger equation and other QED equations I have no clue about. How quantization arises from these equations eventually becomes evident. In the process of solving these equations, one gets a feel for when concepts of quantization come into play. 


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