[time-nuts] a newbie question: where can I purchase 794.7nm VCSEL for building CPT rubidium clock?

mimitech mimitech mimitech at gmail.com
Sat Jun 9 04:54:15 EDT 2018


Thanks Attila for your suggestion.

I prefer the 780/795nm VCSEL scheme for its simplicity. After some
searching, looks like the 780nm VCSELs are also not easy to source,
although other types of 780nm LD are common.

I have purchased small amount of Vixar P/N “795S-0000-BC01” 795nm single
mode VCSEL from a local distributor, price is about $500/pcs. I'm not sure
whether this model could work in CPT rubidium clock.

A more suitable model maybe Oclaro P/N “APM2101013300” 795nm single mode
VCSEL, with unit price $800, which was proved to work as this paper
"A compact atomic magnetometer for cubesats",
https://open.bu.edu/bitstream/handle/2144/16303/Knechtel_bu_0017N_11402.pdf
,

this thesis "Ultra-Low Phase Noise Atomic Clock using Coherent Population
Trapping (CPT) in Rubidium"
http://etheses.whiterose.ac.uk/20073/1/Burtichelov_PhD_Thesis_with_papers_V7.pdf

and also it was used in commercial CPT rubidium clock - Microsemi SA.3xm
series. The cheapest model is SA.31m priced about $1100 at Digikey /
Mouser.

Another paper "VCSEL Laser System for Atomic Clocks"
http://ixnovi.people.wm.edu/documents/NathanBelcherREUPaper.pdf test
several VCSEL from different vendors and found the ULM 794.7 nm single mode
VCSEL can work.

Thanks.

mimitech.


On Tue, 5 Jun 2018 11:11:59 +0200, Attila Kinali <attila at kinali.ch> wrote:
>
> On Mon, 4 Jun 2018 21:31:56 +0800
> mimitech mimitech <mimitech at gmail.com> wrote:
>
> > I'm planning to build a CPT (coherent-population-trapping) rubidium
clock
> > as my next hobby project. The main purpose is to learn the principles
> > behind CPT rubidium clock, and hopefully got similar or better
performance
> > than commercial miniature rubidium clock such as FE-5680A.
>
> Building a CPT clock is slightly more involved than you might think
> at first. The laser diode is only one part of it. You will most likely
> be able to improve on the short-term stability of the FE-5680 (which
> is rather poor). But I doubt you will be able to improve much on
> the long term stability, which is where things actually become
interesting,
> if you use a naive approach.
>
> Nevertheless, I have not seen many 794/795nm diodes around. The only
> one that I have the datasheet of is the one from Vixar.
> You might want want to consider going for the D2 line instead of the
> D1 line, as 780nm diodes are more commonly available than 795nm. You will
> also need to buy several of those and select the ones that come closest
> to the wavelength at the desired opearating conditions (usuall spread
> is +/-1nm to +/-10nm). Do not assume you can tune more than 0.1nm with
> temperature and current (rule of thumb is that you get about 10GHz
> per °C and mA). If you need more tuning range, you will need to add an
> external cavity (can give you up to 5nm range), which then needs to be
> tuned to the 3.45GHz (ie it's length needs to be approximately 8-9cm).
>
> Alternatively, you can get two S1-0780-XXX from Sacher Laser
> (cost IIRC 2500€ each) and keep them 6.9GHz apart (using an optical PLL).
> If you have enough money to spend, I'd go for two Cateye diode laser CEL's
> from Moglabs (cost AFAIK 5000€ each)
>
> No matter what you choose, you will need some wavelength stabilization
> scheme. You can either do that with the vapor cell itself or use
> an additional cell and do a DVALL or a saturated absorption locking.
> Note that this addtional cell will need to be without buffer gas.
> An external cell will offer better stability and thus lower noise,
> which directly translates into higher stability.
>
> As polarisation scheme, I suggest using σ+/σ- as it seems to be more
> robust than the lin/lin schemes.
>
>                         Attila Kinali
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
>                  -- Miss Matheson, The Diamond Age, Neil Stephenson



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