I Laser linewidth in a STIRAP process

  • I
  • Thread starter Thread starter Malamala
  • Start date Start date
  • Tags Tags
    Laser Process
Malamala
Messages
342
Reaction score
28
Hello! In a STIRAP process, for the right parameters (assuming a ##\Lambda##-type transition), the lifetime of the excited state doesn't come into play, so one can achieve very narrow linewidths of the measured transition of interest, regardless of the linewidth of the intermediate, excited state. However, I am not sure I understand how does the laser linewidth come into play. I imagine that if the linewidth of the laser is bigger than the splitting between the 2 levels I am connecting (basically if the laser linewidths are bigger than the difference between the 2 laser frequencies) I won't be able to induce STIRAP (right?), so I can't have arbitrary large laser linewidths (unlike the case of the excited state, whose linewidth can in principle can be as large as possible, given that it is usually very far away from the 2 levels I am interested in). So how does the laser linewidth come into play? Is the transition linewidth actually limited by the laser linewdith? Or the laser linewidth doesn't matter as long as it is smaller than the splitting between the 2 levels? Thank you!
 
Physics news on Phys.org
Malamala said:
So how does the laser linewidth come into play?
STIRAP is a form RAP (adiabatic passage). Adiabatic passage means that the quantum state needs to be preserved. If your laser linewidth is broader than the splitting between the bottom 2 states, then you will progress into a mixed state as the randomized fluctuation of the laser phase will scramble the phase of the atomic state.

Malamala said:
Or the laser linewidth doesn't matter as long as it is smaller than the splitting between the 2 levels?
The broader the laser linewidth, the lower your population transfer efficiency will be with STIRAP. This is again because of loss as the excited state atoms are randomly shuffled back into the ground state by laser noise.

Malamala said:
unlike the case of the excited state, whose linewidth can in principle can be as large as possible, given that it is usually very far away from the 2 levels I am interested in
This isn't inexactly true. The excited state linewidth has to be smaller than 1 over the pulse duration. Otherwise, you'd see spontaneous decay during your STIRAP pulses, and that has a similar effect of scrambling the coherent state during the adiabatic process. The result would also be atoms returning to the ground state.
 
Hi. I have got question as in title. How can idea of instantaneous dipole moment for atoms like, for example hydrogen be consistent with idea of orbitals? At my level of knowledge London dispersion forces are derived taking into account Bohr model of atom. But we know today that this model is not correct. If it would be correct I understand that at each time electron is at some point at radius at some angle and there is dipole moment at this time from nucleus to electron at orbit. But how...
Back
Top