- #1
kelly0303
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Hello! I am reading about Fourier Transform MW spectroscopy in a FB cavity, which seems to be quite an old technique and I want to make sure I got it right.
As far as I understand, this is very similar to normal NRM, i.e. one applies a MW ##\pi/2## pulse which puts the molecules in a linear superposition of 2 levels. This acts as an oscillating dipole which emits energy, and this energy is readout (and amplified by the FB cavity) as a decaying oscillating signal (basically free induction decay signal). From there, doing a FT gives you the frequency of the transition being measured. Is this what is going on?
One thing that I am not totally sure I get, is how do you produce the ##\pi/2## pulse? Unlike non FB case, in this case the MW energy you put in the cavity stays there for a while, and its power gets reduced until it is basically all gone (this depends on the finesse of the cavity). So the molecules see the initial pulse multiple times, as it bounces back and forth between the 2 mirrors.
Does this mean that one needs to calculate the exact initial power needed, accounting for the finesse of the cavity, such that the integral of the (time varying) power of the MW radiation inside the cavity times the time it takes for it to be dissipated to be exactly ##\pi/2##? Or is there some simpler way of doing it and I am overcomplicating the situation.
As far as I understand, this is very similar to normal NRM, i.e. one applies a MW ##\pi/2## pulse which puts the molecules in a linear superposition of 2 levels. This acts as an oscillating dipole which emits energy, and this energy is readout (and amplified by the FB cavity) as a decaying oscillating signal (basically free induction decay signal). From there, doing a FT gives you the frequency of the transition being measured. Is this what is going on?
One thing that I am not totally sure I get, is how do you produce the ##\pi/2## pulse? Unlike non FB case, in this case the MW energy you put in the cavity stays there for a while, and its power gets reduced until it is basically all gone (this depends on the finesse of the cavity). So the molecules see the initial pulse multiple times, as it bounces back and forth between the 2 mirrors.
Does this mean that one needs to calculate the exact initial power needed, accounting for the finesse of the cavity, such that the integral of the (time varying) power of the MW radiation inside the cavity times the time it takes for it to be dissipated to be exactly ##\pi/2##? Or is there some simpler way of doing it and I am overcomplicating the situation.
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