On Mon, 4 Jun 2018 21:31:56 +0800 mimitech mimitech <mimit...@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 _______________________________________________ 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.