I worked on a trapped ion frequency standard 20 years ago, a 12.6Ghz Yb clock. It's still in the lab across from me and looking at it, and the electronics, I think it is the sort of thing that a physicist might contemplate building in his/her garage but ...
Building it took about 10 man years of concentrated effort so the time you would need for a project like this would be the killer, assuming you could buy the spectroscopic lasers and UHV equipment you needed at a price that didn't require refinancing your mortgage. One other vital component is the flywheel oscillator you need to take advantage of the fabulous stability you now have at hand.We had a cryogenic sapphire oscillator for our (microwave) clock. For an optical clock, you're also going to need a frequency comb to get back into the RF domain. Cheers Michael On Wednesday, 2 November 2016, Attila Kinali <att...@kinali.ch> wrote: > On Tue, 1 Nov 2016 09:10:25 -0700 > "Tom Van Baak" <t...@leapsecond.com> wrote: > > > > I really would like to do that. But they are a tad bit expensive. > > > Especially on this side of the big pond. If anyone is willing > > > to part with a Cs standard and want to have it a good home, feel > > > free to contact me :-) > > > > It's true that a cheap GPS receiver is more accurate long-term than > > a surplus cesium standard, but you're right about the "just because" > part. > > To me at least, this time nut hobby is not so much about the pursuit of > > accuracy as it is an appreciation for the variety, ingenuity and > complexity > > of timekeeping. In some cases "how it works" is far more interesting that > > "does it work". > > I think, most of us are in it for the "how it works" and > "how far can I push it". :-) > > > > A used but known working cesium standard can be expensive, but like most > of > > you almost all my gear comes from eBay via automated daily keyword > searches. > > Many of my mil- or telecom-surplus FTS 4050 and HP 5061 were obtained for > > just a couple hundred dollars. You may search for months or even years, > but > > amazing bargains show up. Not all of them work, of course, but the op/svc > > manuals are superb, the design / construction is very repair-friendly, > and > > there's a weird group called time nuts with helpful advice. > > It still is prohibitevly expensive in Europe. There are much fewer > Cs standards going around than in the US in the first place, and there > is also less a tinkering mentality. Ie a lot of companies just say > "it's broken, it's no use for anyone anymore, let's just scrap it" and > thus a lot of stuff ends up in recycling instead of on ebay. Heck, a couple > of years ago i got an 3458 because the company wanted to throw it away. > Mind you, it was in full working condition, only the NVRAM batteries were > low. > > > I still would like to try to build my own atomic clock at some point, > even if it would be a quite costly, and a many years project. > > IMHO the easiest to build would be an Rb or Cs vapor cell using either > dual resonance or coherent population trapping. Cells can be bought > for 300-500€. For a bit more you can get them made to spec. Machining > a resonant cavity from aluminium is pretty easy and cheap these days, > if one wants to go for the dual resonance. The biggest issue for both > types would be the laser system. Either getting the laser diodes selected > (makes them expensive) or build an external cavity for them (creates > the need of a complex control system and not so simple mechanically). > Putting all toghether would probably cost something in the order of > 1000€ to 5000€. > > One up in difficulty would be a passive hydrogen maser. This requires a > vacuum system and things like platinum leaks to generate atomar hydrogen > and state selection magnets. If one knows glass blowing, part of it can > be made using pyrex tubes, which simplifies some stuff (like keeping the > state selection magnets outside the vacuum system). Also, the cavity > needed would be quite big. A normaly used TE011 cavity is huge. One can > load it with aluminia and get it down to 15-20cm diameter, but this > requires > crystaline aluminia to maintain low loss. Maybe one could use other > resonating > structures that are smaller, TE111 or loop-gap resonators have been > proposed. > The biggest cost here is definitely the needed vacuum system. Although > the rough pumps are rather cheap (around 500-1000€ if one does not need > fast pumping) and some of these actually end up on ebay without being > destryoed by "testing", the high vacuum pumps (ion pumps, turbo pumps etc) > are not cheap and need to bought new (the stuff you see on ebay are either > systems that were removed from labs because they don't work anymore, or > were destroyed by "testing" them in free air). > An active hydrogen maser should not be that much more difficult. It mostly > involves a low loss, correctly tuned cavity and low noise detection > electronics. > The input stream of hydrogen atoms needs to be more precisely controlled as > well... > > Another step up in difficulty would be a system using a magneto optical > trap. > Glass cavities with flanges for vacuum system are readily available and > also cheap. Again, the vacuum system is one difficulty, though probably > simpler than for the hydrogen maser (less parts that need to be custom > made). > But the requirements for the vacuum are a bit higher. The laser system > poses > a similar difficult as with the CPT system above, but now there are more > lasers and all need to be locked to eachother. The traping laser also need > to be directed at the cavity from 6 sides, all meeting in the center of the > cavity, which makes alignment problematic. This is also the first system > that offers to be a primary standard, although it probably does not get to > the stability of a 5071, as the trapping lasers will induce a light shift > that is not so easy to control unless one goes for the expensive laboratory > grade lasers. > > Next on the list would be an Hg ion trap. But there are so many parts > in such a system that are not easily bought and require a very good > understanding of the physics involved to design custom parts, that > it becomes almost unrealistic that an amateur could be build one at home. > Same goes for ion and neutral atom optical clocks. Yes, they can be build, > yes the principle is simple, but getting it actually to work needs a lot > of understanding and tinkering. > > > Ah... I'm dreaming again :-) > > 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 > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com <javascript:;> > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.