[time-nuts] Re. DIY atomic "resonator"

Wed Apr 12 20:23:48 EDT 2017

Typically External Cavity diode lasers use either the Littrow or the Littman-Metcalf configurations.

A typical Littrow configuration is:

http://www.moglabs.com/uploads/2/4/2/1/24212474/manual_ecd_rev4.20.pdf

Alternatively a cat eye external cavity can be used:

http://www.moglabs.com/uploads/2/4/2/1/24212474/moglabs_cel002_manual_rev108.pdf

To assist with tuning the laser a wavemeter is helpful:

http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/31/004/31004208.pdf

Other variants based on optical wedges or even a simple grating can also be used together with a CCD camera or equivalent to achieve an accuracy approaching a few pm.

Whilst AR coated laser diodes work best its also possible to use uncoated laser diodes.

Such diodes have been successfully used for atomic spectroscopy of rubidium vapour by several groups.

Temperature control of the laser diode and cavity are the most critical issues.

One can easily adapt standard optical mounts to make one's own ECDL but temperature control is critical for use in a rubidium standard.

Locking the laser to the absorption line of interest relaxes the required long term stability of the ECDL itself.  

Bruce

> 
>     On 13 April 2017 at 08:55 Bert Kehren via time-nuts <time-nuts at febo.com> wrote:
> 
>     Looking back at the dialog I started on Rb’s and the repeated returns to
>     that subject allow me to make some comments, observations and
>     recommendations.. I stayed on purpose away from participating but learned a lot. It also
>     resulted in some off list dialogs with members working on the subject off
>     list.
>     Rick’s discussion on why to use two frequencies was for me an eye opener
>     and gives me clear directions on how to proceed on frequency generation. The
>     single frequency project is dumped. Corby’s work on filters again
>     influences our future steps. Using a laser diode and its challenges again an eye
>     opener and a challenge. We have time nuts that have working systems.
>     Let’s be honest, we have members with super knowledge but very few have
>     the appetite to do something with it in the form of hardware. Here is my
>     proposal that is based on walk before run.
>     FRK and M100 are next to the HP 5065A the most promising Rb’s in what we
>     like to do. They are easy to work on specially when you are 75/78 and in my
>     case have a macular hole.
>     Optical Filter. Corby actually did insert a filter in a M100 did however
>     not notice an improvement. When we discussed it come to find out he forgot
>     to change the time constant so the cell did not control the performance.
>     This was years ago and like many of us has his hands full with projects. He
>     decided to pass his M100/FRK to an other time nut and focus on HP and Maser.
>     We all benefit from these efforts.
>     Back to filter we have dissected a FRK and a M100 and are convinced that
>     there is a room for a filter, in case of the FRK, very easy. Corby used a
>     M100, in my opinion more of a challenge. Will not try it. After discussions
>     with Corby I now understand that the filter does not filter out a particular
>     wavelength but most the noise that Rb lamps produce as seen on optical
>     spectrum analyzers. It improves signal noise ratio after all that is what is
>     all about. Once we have completed our current projects we may do so.
>     We are also considering to review the frequency generation using Rick’s
>     postings as guidance. All this needs measuring capabilities which is what we
>     are working on. I am fortunate to have access to Corby’s Maser but Juerg
>     does not have that. We are working on a solution.
>     There are many FRK/M100’s out there some with low output lamps that would
>     be a natural for a Laser Diode replacement. The mechanical makeup begs for
>     a Laser solution. The two units have a cell in size only second to HP5065A
>     Going to laser would also allow to reduce cell temperature again
>     contributing to an improved signal noise ratio,
>     This is way off our expertise but it would be nice if some one would take
>     the ball and run with it. I am convinced from off list conversations that
>     $1000 is a reasonable goal.
>     There is no guarantee that we will do the filter depending what our
>     results will be on our present work so again maybe some one would carry that
>     ball.
>     Both can be a first step for future work. WALK
>     Bert Kehren
> 
>     In a message dated 4/11/2017 12:02:09 P.M. Eastern Daylight Time,
>     attila at kinali.ch writes:
> 
>     On Tue, 11 Apr 2017 07:31:01 +0000
>     Andre <Andre at Lanoe.net> wrote:
> 
>         > > 
> >         Has anyone else either built an atomic clock around a bare Rb lamp
> >         module "core" or attempted
> > 
> >         to make a hydrogen maser?
> > 
> >     > 
>     Building my own Rb vapor cell standard or H-maser is on my list
>     of Things-I-have-to-do-before-I-die :-)
> 
>     If I had to do one of those now, I would go for a Rb vapor cell
>     with dual-resonance using an external cavity laser diode for pumping.
> 
>     The electronics for such a thing are relatively easy, if you are not
>     afraid of Jiga-Hurts and using these pesky QFN packages. But it isn't
>     cheap either. There was a discussion started by Bert[1] where I ventured
>     a rough calculation what I think it wold cost. Though I think I have
>     understimated the cost of an ECLD (it's more like 1k-5k from what I have
>     read)
> 
>     Attila Kinali
> 
>     [1] search for "thinking outside the box" in the archives
> 
>     --
>     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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