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Sub-Doppler laser cooling of $^{39}$K via the 4S$\to$5P transition

by Govind Unnikrishnan, Michael Gröbner, Hanns-Christoph Nägerl

This is not the current version.

Submission summary

As Contributors: Govind Unnikrishnan
Arxiv Link:
Date submitted: 2019-02-22
Submitted by: Unnikrishnan, Govind
Submitted to: SciPost Physics
Domain(s): Experimental
Subject area: Atomic, Molecular and Optical Physics - Experiment


We demonstrate sub-Doppler laser cooling of $ ^{39} $K using degenerate Raman sideband cooling via the 4S$_{1/2} \rightarrow $5P$ _{1/2} $ transition at 404.8 nm. By using an optical lattice in combination with a magnetic field and optical pumping beams, we obtain a spin-polarized sample of up to $5.6 \times 10^{7}$ atoms cooled down to a sub-Doppler temperature of 4 $\mu $K, reaching a peak density of $3.9 \times 10^{9}$ atoms/cm$ ^{3} $, a phase-space density greater than $ 10^{-5} $, and an average vibrational level of $ \langle \nu \rangle=0.6 $ in the lattice. This work opens up the possibility of implementing a single-site imaging scheme in a far-detuned optical lattice utilizing shorter wavelength transitions in alkali atoms, thus allowing improved spatial resolution.

Current status:
Has been resubmitted

Ontology / Topics

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Sub-Doppler cooling

List of changes

The changes are indicated in the responses to the referee reports.

Reports on this Submission

Anonymous Report 3 on 2019-3-12 Invited Report


I am now fine with publication.

  • validity: -
  • significance: -
  • originality: -
  • clarity: -
  • formatting: -
  • grammar: -

Anonymous Report 2 on 2019-2-26 Invited Report


I am generally happy with the authors response to my questions. I only have a few minor suggestions.

(a) In section 2.2, the sentence beginning 'A second \sigma^- polarised beam (so called "repumper)...' is confusing as this beam doesn't deplete the F=2 manifold but rather keeps everything in the F=2. Also it appears in the middle of the paragraph and just gets in the way of the flow of the argument. I would move it to a footnote (as suggested by one of the other referees) or at least to the end of the paragraph where you could say 'Note that an sigma polarised repumper beam tuned to the ... transition (see fig 3) is also required to prevent population of the F=1 groundstate.'

(b) Both the power and intensity of the polariser beam are now given in Fig 6 but not in Fig 5 - it would be good to have in both places to make it clear that the same power was used in both cases.

(c) On p13, it would be helpful to replace the sentence beginning 'At \delta_p = 4.9MHz, where cooling is only marginally less efficient,...' with 'At \delta_p = 4.9MHz, where cooling is only marginally less efficient than the optimum detuning of \delta_p = 6.9MHz ,...'. The previous thing that was referred to was the \delta_p = 0.9MHz case which as I understand it is not what is being compared to.

  • validity: -
  • significance: -
  • originality: -
  • clarity: -
  • formatting: -
  • grammar: -

Author Govind Unnikrishnan on 2019-03-24 (in reply to Report 2 on 2019-02-26)
answer to question

We thank the referee for the additional comments. We have made all the three recommended changes.

(a) In section 2.2, we moved the relevant sentence to the end of the paragraph. We now say, "Note that a second $ \sigma^- $-polarized beam (so called ``repumper"), which is tuned to the 4S{1/2} F=1 ->4P1/2 F=2 transition (see Fig. 3), depletes population in the 4S 1/2 F=1 manifold", at the end of the paragraph.

(b) Both the power and intensity of the polarizer beam is now mentioned in all the three relevant figures (Fig. 4 (a) ,5, and 6).

(c) As suggested, we have now made it explicit that the comparison is made to the detuning at 6.9 MHz.

Anonymous Report 1 on 2019-2-25 Invited Report


I am satisfied that the authors have satisfactorily addressed my comments from the initial round of review, and recommend publication.

  • validity: high
  • significance: good
  • originality: good
  • clarity: high
  • formatting: excellent
  • grammar: excellent

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