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

Bob kb8tq kb8tq at n1k.org
Sat Jun 9 10:12:03 EDT 2018


For several decades the Efratom FRK was the only “compact” Rb on the market. By today’s standards it’s a bit 
large, but in that era it was quite small. They went through a couple of re-designs over the years, but kept the 
basic form factor and nomenclature. The M-100 is the military version. EG&G ( and possibly others) cloned the 
package in an attempt to compete with Efratom. You see very few EG&G’s and a *lot* of Efratom’s ….


> On Jun 9, 2018, at 9:34 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> What is an 'FRK'?
> Thanks,
> Dana
> On Sat, Jun 9, 2018 at 7:51 AM, ew via time-nuts <time-nuts at febo.com> wrote:
>> Having followed the conversation and having looked at the p[possibility
>> using a FRK with laser diode, it is low on our list because of all the
>> ongoing projects but please if you want to spend time and money use any
>> thing but a FE5680. I was one of the first using it and noticed and posted
>> a 4 Hz constant deviation using my Tracor 527 E subsequent confirmed by the
>> attached. Do not have info as to who posted it.
>> Using a FRK is the easiest way to do so if interested contact me off list,
>> based on our tests is a close second to the HP 5065A.
>> Bert Kehren
>> In a message dated 6/9/2018 7:23:45 AM Eastern Standard Time,
>> bruce.griffiths at xtra.co.nz writes:
>> Theres also
>> http://www.photonics.philips.com/application-areas/sensing/components
>> and
>> https://www.sacher-laser.com/home/industriallasers/point_
>> and_line_laser_module/industrial_laser_modules/micron_laser.html
>> Bruce
>>> On 09 June 2018 at 20:54 mimitech mimitech <mimitech at gmail.com> wrote:
>>> 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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