[time-nuts] Current state of optical clocks and the definition of the second

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Tue Jan 13 12:46:01 EST 2015

On 12 January 2015 at 12:34, Attila Kinali <attila at kinali.ch> wrote:
> Hi,
> I just stumbled over this [1] nice article by Fritz Riehle that might be
> of interest to others as well.
>                         Attila Kinali
> [1] "Towards a Re-definition of the Second Based on Optical Atomic Clocks",
> by Fritz Riehle, 2015
> http://arxiv.org/abs/1501.02068

I had a brief read. Equation 1 made me wonder what could be achieved
with a cheap HeNe laser. It should be fairly easy to mix a couple of
HeNe lasers on a photodiode and look at the difference frequency
between them, so gaining insight into their stability.  A quick check
on Wikipedia


indicates a spectral width of 0.002 nm.

The common 632.8 nm laser has a frequency of 4.7 x 10^14 Hz, or 470 THz.

Of course I'm not suggesting a HeNe would provide the stability of
cutting edge research laser optical clock, but they are easily within
the budget of a hobbyist and could be a bit of fun to try to measure
their stability/phase noise. The tricky bit would be getting 470 THz
down to 10 MHz, but a cheap and quick experiment would prove whether
it is a total waste of time or not.


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