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CCP4BB  April 2011

CCP4BB April 2011

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Subject:

Re: Femtosecond Electron Beam

From:

Jacob Keller <[log in to unmask]>

Reply-To:

Jacob Keller <[log in to unmask]>

Date:

Thu, 14 Apr 2011 20:40:00 -0500

Content-Type:

text/plain

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Parts/Attachments

text/plain (264 lines)

One of the figures they cite is 2.5 electrons per um^2, which I think
means once the whole bunch has gone through. That struck me as being
pretty far from where one needs to be to get structures. Do you know
off hand a comparable figure for the FEL experiment? I assume it would
be many orders of magnitude greater. For example, how many total
photons were in each bunch with the FEL?

JPK

On Thu, Apr 14, 2011 at 5:24 PM, Colin Nave <[log in to unmask]> wrote:
> 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:[log in to unmask]] On Behalf Of
>> Petr Leiman
>> Sent: 14 April 2011 22:59
>> To: [log in to unmask]
>> 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:[log in to unmask]] On Behalf
>> Of
>> >> Petr Leiman
>> >> Sent: 14 April 2011 21:07
>> >> To: [log in to unmask]
>> >> 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:[log in to unmask]] On Behalf
>> >> Of
>> >>>> Petr Leiman
>> >>>> Sent: 14 April 2011 16:23
>> >>>> To: [log in to unmask]
>> >>>> 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 [[log in to unmask]] on behalf of
>> Colin
>> >>>> Nave [[log in to unmask]]
>> >>>> Sent: Thursday, April 14, 2011 16:50
>> >>>> To: [log in to unmask]
>> >>>> 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:[log in to unmask]] On
>> Behalf
>> >> Of
>> >>>>> Jacob Keller
>> >>>>> Sent: 14 April 2011 14:39
>> >>>>> To: [log in to unmask]
>> >>>>> 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: [log in to unmask]
>> >>>>> *******************************************
>



-- 
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
cel: 773.608.9185
email: [log in to unmask]
*******************************************

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