spin noise

Thank you for posting !! although $32 seems a bit high for an article

Interesting! Is there anything advantageous to 'applying' specific fields, intead of simply 'observing' fields? Maybe, like pull out a molecule, or hold it still while everything else is 'flushed' away?

It's on arxiv:

-- john

Haven't got time to read the paper just now, but it sounds like a good application for a laser noise canceller.

Using two separate paths doesn't work well because you can't match the phase shifts to the required accuracy. By wiring two PDs in series (parallel at AC due to the supply bypasses), you get only one signal path and one set of circuit strays, so it's only the transit time behaviour of the PDs and optical delays that can differ.

The noise canceller is sort of an intermediate situation, where you have very nearly the same strays but not exactly. (The high frequency tweaks in my fancy ones are one answer to that problem.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net

Thanks!

,

Well when you apply the field (say the light field in optical pumping which is the tradition way to see the above (magnetic) splitting of ground state of the atomic system) then it turns into a system that is not in thermal e quilibrium and this (I guess.. I not at all a theorist) means that the stat es are perturbed a bit. Where the field free method has no such perturbatio n... But the signals are much much smaller!! The other thing you might wor ry about is the the RF fields used to probe the states can also cause chang es. Again I have no idea how big these effects are.

George H.

w to do it from google groups... could someone help?)

My handwavy understanding.

1.) there's fluctuations in the spins.. (noise) 2.) if the system has resonances, then noise driving those resonances will show up the in noise spectrum. (I think of white noise into a band pass fi lter... and what you see at the output.) 3.) 'Slightly' off resonance faraday rotation is used to detect the fluctua tions in the spin states and the ground state resonaces are thus observed. (So there's a term in the denominator of faraday signal that goes as a res onant frequency (this is now an optical resonance.. or maybe a better word is an optical transition frequency) minus the applied optical frequency.. t his kinda blows up when the two are equal.. and when they are near equal yo u get a big enhancement of the signal.)

Oh, thanks Phil I forgot about balancing the phase shifts. (path lengths)

Say with two PD's in a box how do you do the optical alignment. (or do you 'cheat' and use fibers. I scribbled down this gizmo, where the entire bo x moves in x and y (assume light direction is z) and then one PD does and i ndependent x translation, and the other a y- . A bit complicated. Hmm maybe just do everything with mirrors, so a separate x/y mirror adjustm ent for each PD?

George H.

Fibres are very unlikely to improve anything. They cause a lot more problems than they cure, except when one of their virtues (e.g. unsurpassed pointing stability) is more important than their vices (horrible, unstable etalon fringes, polarization problems, and sensitivity to temperature and vibration).

Normally you don't need to tweak the optical paths that closely, unless the modulation frequency is pretty high. Phase shifts enter linearly, so the cancellation limit for a given phase shift is

A_max = 20 log(delta phi).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net