Well I saw one of the images was 200 fC, which I think is ~1.3 million
electrons, which I thought was pretty amazing considering the signal
in that figure (attached). Then again, gold foil is not protein, is
it...
JPK
On Thu, Apr 14, 2011 at 4:13 PM, Colin Nave <[log in to unmask]> 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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