Petr Well, not sure - are we doing imaging or diffraction/scattering? What energy are the electrons in these sources? The idea of pulsed sources is to put more electrons/A^2 and still beat radiation damage. Can one do this when there are only around 10^6 electrons in perhaps a rather divergent beam? Shall we discuss off line (with Jacob) and present our conclusions when/if we get agreement? Regards Colin
> -----Original Message----- > From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of > Petr Leiman > Sent: 14 April 2011 22:59 > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] Femtosecond Electron Beam > > Colin, > > We know that with a dose of 20-30 electrons per A^2, a lot of image > processing, and insane amount of luck, one can reconstruct cryoEM > images to 3 A resolution or better. A typical protein molecule is say > 100 A in diameter, which is ~8000 A^2 in projection. So, in an ideal > case one needs only 240,000 electrons to record an image of a protein > molecule with a signal extending to 3A resolution. > > Jacob, > > Yes, you are correct. Jom et al. manipulate electron bunches of 1+ Mln > electrons, which should be enough to record an image of a protein > molecule. > > Best, > > Petr > > > On Apr 14, 2011, at 11:13 PM, Colin Nave wrote: > > > Petr > > Yes, I saw the figure. Similar ones appear in the Hastings et. al. > paper (the SLAC one I referenced). They use a much higher energy beam > to get the short pulse length. > > > > I still believe the issues are > > > > 1. For diffraction, can you get a low enough electron beam divergence > to resolve larger unit cells? The peaks appear rather broad in the foil > experiments. Luiten et. al. believe they can extend the technique to > resolve cells of a few tens of nm which would be fine. Their ideas for > doing this appear to be quite novel. I don't know if they have > demonstrated this though. > > 2. Given the above, will there be enough electrons in one of the > short pulses to get enough statistics for a biological molecule or > protein nano-crystal? I have not seen calculations for this for > electron beams (as has been done for the FEL x-ray beams). Actually it > should be quite easy to do as the cross sections are all available. > > 3. For imaging (i.e. using an objective lens) is the blurring I > mention going to be a fundamental limitation and what will this > limitation be? > > > > These instruments would be useful for material science applications > and fast chemistry investigations where some of the above issues would > not be relevant. Not sure for imaging biological molecules. We will > see. > > > > Finally saying Phys Rev Let is not a high impact journal would > probably upset my physicist colleagues - that's fine though! > > > > Regards > > Colin > > > >> -----Original Message----- > >> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf > Of > >> Petr Leiman > >> Sent: 14 April 2011 21:07 > >> To: CCP4BB@JISCMAIL.AC.UK > >> Subject: Re: [ccp4bb] Femtosecond Electron Beam > >> > >> Dear Colin and all interested in the FEL development. > >> > >> Please look at the figures in the first link I mentioned. Jom Luiten > et > >> al. are able to record a 1.25 A resolution diffraction pattern of a > >> gold foil using a pulse compressed to 50 fs. Ahmed Zewail is a > pioneer > >> of the technique but as far as I know his instrumentation is nowhere > >> near Jom's amazing machine. > >> > >> Why Jom's paper was not published in one of the high profile > journals, > >> ahem, magazines, is a mystery to me. > >> > >> Petr > >> > >> On Apr 14, 2011, at 9:11 PM, Colin Nave wrote: > >> > >>> Petr has provided the Eindhoven links. > >>> > >>> For more details on fast electron imaging (as opposed to > diffraction) > >> see https://e-reports-ext.llnl.gov/pdf/343044.pdf > >>> > >>> Apparently stochastic scattering of the electrons at the high > current > >> densities necessary for short pulsed sources result in blurring in > the > >> image. The paper says that 10nm spatial and 10ps temporal resolution > >> could be achieved with 5MeV electrons and annular dark field > imaging. > >>> > >>> Of course more recent developments at Eindhoven and elsewhere might > >> get round some of the limitations. > >>> > >>> > >>> Colin > >>> > >>>> -----Original Message----- > >>>> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf > >> Of > >>>> Petr Leiman > >>>> Sent: 14 April 2011 16:23 > >>>> To: CCP4BB@JISCMAIL.AC.UK > >>>> Subject: Re: [ccp4bb] Femtosecond Electron Beam > >>>> > >>>> People are looking into how to fit the old retired MeV microscopes > >> with > >>>> pulsed electron guns (problem is there are very few of those > beasts > >>>> left). If this works, such a machine will produce equivalent > results > >> to > >>>> FEL but at a fraction of the cost. > >>>> > >>>> The group at Eindhoven, which Colin had mentioned, has already > made > >> a > >>>> significant progress in achieving both time and spatial coherence. > >> They > >>>> are able to manipulate electrons in ultrashort electron bunches > akin > >> to > >>>> spins in an NMR machine: > >>>> http://prl.aps.org/abstract/PRL/v105/i26/e264801 > >>>> http://jap.aip.org/resource/1/japiau/v109/i3/p033302_s1 > >>>> And this is due to the fact that electrons can be focused with > >> lenses. > >>>> Amazing stuff. We will hear more about this for sure. > >>>> > >>>> Sincerely, > >>>> > >>>> Petr > >>>> > >>>> ________________________________________ > >>>> From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of > Colin > >>>> Nave [colin.n...@diamond.ac.uk] > >>>> Sent: Thursday, April 14, 2011 16:50 > >>>> To: CCP4BB@JISCMAIL.AC.UK > >>>> Subject: Re: [ccp4bb] Femtosecond Electron Beam > >>>> > >>>> Jacob > >>>> Very good question. > >>>> > >>>> People are considering this sort of thing. See for example > >>>> http://www-spires.slac.stanford.edu/cgi-wrap/getdoc/slac-pub- > >> 12162.pdf > >>>> > >>>> Due to coulomb explosion one normally needs MeV beams to get the > >> short > >>>> bunch length. MeV beams also give a more reasonable penetration > >> depth > >>>> (not relevant for single molecules). I think the problem is that > the > >>>> divergence is too high to resolve diffraction spots from protein > >>>> crystals (or in other words insufficient coherence). Probably fine > >> for > >>>> many small molecule crystals though. You mentioned single > molecules, > >>>> presumably protein molecules and I think the same would apply if > >> trying > >>>> to observe the scattering. > >>>> > >>>> One could try imaging (i.e. with an electron lens) rather than do > >>>> diffraction. I presume this is what you mean by "focussed to solve > >> the > >>>> phase problem". However, I understand that there are problems with > >> this > >>>> as well for MeV beams but I can't remember the exact details. Can > >> look > >>>> it up if you are interested. > >>>> > >>>> There could of course be technical advances which would make some > of > >>>> these ideas possible. I think a group at Eindhoven have plans to > get > >>>> round some of the problems. Again I would have to look up the > >> details. > >>>> > >>>> Regards > >>>> Colin > >>>> > >>>> > >>>> > >>>> > >>>> > >>>>> -----Original Message----- > >>>>> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On > Behalf > >> Of > >>>>> Jacob Keller > >>>>> Sent: 14 April 2011 14:39 > >>>>> To: CCP4BB@JISCMAIL.AC.UK > >>>>> Subject: [ccp4bb] Femtosecond Electron Beam > >>>>> > >>>>> Dear Crystallographers, > >>>>> > >>>>> is there any reason why we are not considering using super- > intense > >>>>> femtosecond electron bursts, instead of photons? Since the > >> scattering > >>>>> of electrons is much more efficient, and because they can be > >> focussed > >>>>> to solve the phase problem, it seems that it might be worthwhile > to > >>>>> explore that route of single-molecule structure solution by using > >>>>> electrospray techniques similar to the recently-reported results > >>>> using > >>>>> the FEL. Is there some technical limitation which would hinder > this > >>>>> possibility? > >>>>> > >>>>> JPK > >>>>> > >>>>> -- > >>>>> ******************************************* > >>>>> Jacob Pearson Keller > >>>>> Northwestern University > >>>>> Medical Scientist Training Program > >>>>> cel: 773.608.9185 > >>>>> email: j-kell...@northwestern.edu > >>>>> *******************************************
