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

[Dr. David Kirkby (Kirkby Microwave Ltd)]

Dr David Kirkby
Managing Director
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3
6DT, United Kingdom
Registered in England and Wales as company number 08914892
http://www.kirkbymicrowave.co.uk/
Tel 07910 441670 / +44 7910 441670 (0900-2100 GMT)
On 13 Jan 2015 20:39, "Neville Michie" <namichie at gmail.com> wrote:
> THe stability /accuracy of lasers is entirely dependent on the cavity
length.
> Materials used are usually invar or silica, so you are no better off than
> with a quartz crystals.
> They are just a resonant cavity.
> cheers,
> Neville Michie

I do realise that thermal stability is important.  The pulsed titanium
sapphire laser I used during my PhD took about 8 hours to become stable,
and that had a lump of invar in it which was probably about 1.2 m long and
120 mm in diameter.  But to say that the stability/accuracy depends
entirely on the cavity length is a gross simplification.  Someone posted a
link to some information on getting  narrow linewidths from cheap
semiconductor lasers with something as simple as a piece of glass in front.
That does nothing to stabilise the cavity length.

There's a free webiminar on the 29th Jan at 1300 PST with the title "Laser
Test of RIN, Linewidth and Optical Noise Parameters".

http://www.microwavejournal.com/events/1310-laser-test-of-rin-linewidth-and-optical-noise-parameters

Dave.