Ungar paper, Figure 6

[Sid Wright]

Hi,

Before starting to build simulations with pylcp, and colleague and I built my own OBE solver, and used it also to verify the Ungar et al. paper results for sodium. Myself and a colleague found good agreement with figure six of the Ungar paper, for all configurations except "corkscrew", where we found a disagreement of 10% or more in the local minimum of the force against velocity at around v=2*v_0. However, we appear to be in good agreement with the pylcp online example which simulates for the same parameters (although I noticed that you used slightly different parameters in your original publication about the code package). 

Did you ever figure out what the cause of this discrepancy is? I was a bit surprised that such a disagreement appears in corkscrew polarisation configuration, where the steady-state force is not changing along the direction of laser propagation and so no "spatial averaging" over a wavelength is necessary. I wonder if you could add a comment to the examples page noting that this discrepancy exists with the article, as it may leave others scratching their heads for some time when sanity checking. 

Best wishes,

Sid

[Eckel, Stephen P. (Fed)]

Hello again Sid,

 

I must admit that I never actually looked at the agreement with this level of detail.  When we coded the examples, our attitude was more like “well, it looks the same.”  I am at a bit of a loss to explain the discrepancy, particularly when all the other polarization cases agree.  While there may not be a spatial average, there is a temporal one for moving atoms, since the two lasers in the corkscrew have different Doppler-shifted detunings.  I am tempted to say that maybe Ungar et. al. did not get the temporal average to converge?  This seems most likely since your independent calculation and pylcp agree.

 

I am curious if any other users have any ideas.

 

No matter what, for the next bugfix release, which should be coming soon, we’ll add a note to the example about it.

 

Best,

 

-Steve

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[Sid Wright]

Thanks a lot for your reply Steve. I suspect the parameters in Ungar for that particular force curve do not match the plot somehow, as they clearly show the time-dependence of populations throughout that paper. One thing I did check was whether it was down to any ambiguity in beam intensity per beam versus total intensity - I don't think it can be this. Anyhow, thanks for looking into this and responding so fast! 

Best, Sid