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

### Submission summary

 As Contributors: Govind Unnikrishnan Arxiv Link: https://arxiv.org/abs/1811.02185v2 Date submitted: 2019-02-22 Submitted by: Unnikrishnan, Govind Submitted to: SciPost Physics Domain(s): Experimental Subject area: Atomic, Molecular and Optical Physics - Experiment

### Abstract

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:
Editor-in-charge assigned

### List of changes

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

### Submission & Refereeing History

Resubmission 1811.02185v2 on 22 February 2019
Submission 1811.02185v1 on 7 November 2018

## Reports on this Submission

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### Report

I am now fine with publication.

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

### 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: -

### 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