[time-nuts] Why Cesium and Rubidium only

[Dr Bruce Griffiths]

Bob Paddock wrote:
> On Friday 27 July 2007 04:14, Dr Bruce Griffiths wrote:
>
>   
>> 22GHz, 
>> (15GHz)
>> (~40.5 GHz) than either the caesium
>> (9.192GHz) or rubidium   
>> (6.8GHz)
>>     
>
> Anything happening in the THz range, that anyone knows of?
>
>
>
>   
Bob

NIST are working on both Calcium (456 THz) and Ytterbium (519 THz) 
neutral atom optical clocks.
They have also done some work on the Mercury ion (1064.7 THz) optical 
standard.


Bruce