Suppose I pass a laser that is locked to a certain transition through an AOM. Then the 1st order diffracted beam will still remain locked with a certain frequency difference from the initial frequency of the laser.
But if I pass a laser that is in scanning mode(scanning in the sense that it is not locked to any transition), then will that frequency difference generated by AOM in the 1st order, still, make any sense?. In order words will the 0th order and 1st order beam will have any frequency separation. If yes how can we know that in an EIT system where I have one locked laser and two scanning lasers having a certain frequency difference?
The AOM will always cause a frequency shift between the diffracted beam and the undiffracted beam. Suppose you have a single-mode laser with wavelength \lambda then the optical frequency of that laser is c/\lambda. This is typically a very large number in the range of 10^14 Hz. The diffraction due to the interaction with the traveling acoustic wave then shifts this frequency by the relatively small modulation frequency, which is in the range of 10^7 to 10^9 Hz. This shift can either be an upshift or a downshift, depending on the orientation of the AOM relative to the beam. If you recombine both beams on a photodetector, you will find a beat note at the modulation frequency, but you cannot judge whether the light was upshifted or downshifted.
The frequency shift in the first diffraction order appears completely independent on whether your laser was locked to some transition or free-running or scanning.
Thank you very much sir for the information. It would be a great help to me.
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