Bernhard Yes I stand corrected, 'coherence length' it is. I think I did mean 'coherence' and not 'correlation', it's just that I had 'correlation' on my mind from something else I was doing. What I need is a 'concept checker' in addition to a spelling & grammar checker!
-- Ian > -----Original Message----- > From: owner-ccp...@jiscmail.ac.uk > [mailto:owner-ccp...@jiscmail.ac.uk] On Behalf Of Bernhard Rupp > Sent: 29 January 2009 18:59 > To: 'Nave, C (Colin)'; CCP4BB@JISCMAIL.AC.UK > Subject: RE: [ccp4bb] X-ray photon correlation length > > Ok, following seems to be correct: > > > > a) interaction length = mean free path : relevant for absorption > > b) correlation length = time correlation between photons > : relevant for multi-photon scattering > > c) coherence length = longitudinal coherence length : > relevant for single photon scattering. > > > > It follows from Heisenberg for a Lorentzian source (anode) > with natural emisson line width per > > formula on p 5007 of Colin's ref > > > > Lc=(2/pi)lambda**2/delLambda > > > > Using 8084 eV and 2.1 eV respectively for Cu, I obtain ~3800 > A coherence length for a Cu (anode) X-ray photon > > > > The pre-factor is different for other source types like synchrotron. > > > > In any case I would accept the vague term of 'a few 1000 A' > or 'several 1000 A' as a general statement for > > coherence length in materials where the interaction length is > larger (practically always). > > > > Does this sound reasonable? > > > > BR > > > > > > From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On > Behalf Of Nave, C (Colin) > Sent: Thursday, January 29, 2009 10:14 AM > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] X-ray photon correlation length > > > > Bernard > > I guess this came from > > "Aren't detwinning methods appropriate only in the case of > true twin domains which are larger than the X-ray photon > correlation length in order for the assumption to be valid > that |F|^2 from each domain can be summed? This wouldn't give > rise to the apparent 'diffuse scatter' phenomenon." > > > > I think this is normally called coherence length. Probably > best not to think of photons at all but waves (though there > is an equivalent quantum mechanical treatment based, as V > Nagarajan says, on the uncertainty principle). I don't think > the domains have to be larger then the correlation (sorry > coherence) length of the incident x-rays in any case. They > have to be large enough to give an intensity which can be > integrated. If smaller domains are present, the intensity > just spread out a bit more.When the domains are very large, > the size of the spots would be determined by the incident > beam properties. > > > > The article cited some years ago on CCP4BB gives a primer on all this > > J. Phys.: Condens. Matter 16 (2004) 5003-5030 PII: > S0953-8984(04)75896-8. Coherent x-ray scattering Friso van > der Veen1,2 and Franz Pfeiffer1 > > http://www.iop.org/EJ/article/0953-8984/16/28/020/cm4_28_020.p > df?request-id=8848d3f0-5a4b-4ffe-8ea4-c1eabfaf1657 > > > > Cheers > > Colin > > > > ________________________________ > > From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On > Behalf Of Bernhard Rupp > Sent: 29 January 2009 17:51 > To: CCP4BB@JISCMAIL.AC.UK > Subject: [ccp4bb] X-ray photon correlation length > > I always wondered - how is the X-ray photon correlation > length defined > > and where do I find it? This is not the interaction length, > I assume. > > > > So, to the physicists: How large is the 'X-ray photon > correlation length' > > for a given wavelength in a given material? > > > > I had the impression that the term photon correlation refers > > to the time correlation of the scattering such as in photon > correlation spectroscopy... > > > > Best regards, BR > > > > > > This e-mail and any attachments may contain confidential, > copyright and or privileged material, and are for the use of > the intended addressee only. If you are not the intended > addressee or an authorised recipient of the addressee please > notify us of receipt by returning the e-mail and do not use, > copy, retain, distribute or disclose the information in or > attached to the e-mail. > Any opinions expressed within this e-mail are those of the > individual and not necessarily of Diamond Light Source Ltd. > Diamond Light Source Ltd. cannot guarantee that this e-mail > or any attachments are free from viruses and we cannot accept > liability for any damage which you may sustain as a result of > software viruses which may be transmitted in or with the message. > Diamond Light Source Limited (company no. 4375679). > Registered in England and Wales with its registered office at > Diamond House, Harwell Science and Innovation Campus, Didcot, > Oxfordshire, OX11 0DE, United Kingdom > > > > ________________________________ > > > Scanned by iCritical. > > > > Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing i.tic...@astex-therapeutics.com and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
