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Single-molecule imaging with longer X-ray laser pulses.

Martin AV, Corso JK, Caleman C, Timneanu N, Quiney HM - IUCrJ (2015)

Bottom Line: One of the key reasons for this success is the 'self-gating' pulse effect, whereby the X-ray laser pulses do not need to outrun all radiation damage processes.As a result, serial femtosecond crystallography does not need to be performed with pulses as short as 5-10 fs, but can succeed for pulses 50-100 fs in duration.The results suggest that sub-nanometre single-molecule imaging with 30-50 fs pulses, like those produced at currently operating facilities, should not yet be ruled out.

View Article: PubMed Central - HTML - PubMed

Affiliation: ARC Centre of Excellence for Advanced Molecular Imaging, School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia.

ABSTRACT
During the last five years, serial femtosecond crystallography using X-ray laser pulses has been developed into a powerful technique for determining the atomic structures of protein molecules from micrometre- and sub-micrometre-sized crystals. One of the key reasons for this success is the 'self-gating' pulse effect, whereby the X-ray laser pulses do not need to outrun all radiation damage processes. Instead, X-ray-induced damage terminates the Bragg diffraction prior to the pulse completing its passage through the sample, as if the Bragg diffraction were generated by a shorter pulse of equal intensity. As a result, serial femtosecond crystallography does not need to be performed with pulses as short as 5-10 fs, but can succeed for pulses 50-100 fs in duration. It is shown here that a similar gating effect applies to single-molecule diffraction with respect to spatially uncorrelated damage processes like ionization and ion diffusion. The effect is clearly seen in calculations of the diffraction contrast, by calculating the diffraction of the average structure separately to the diffraction from statistical fluctuations of the structure due to damage ('damage noise'). The results suggest that sub-nanometre single-molecule imaging with 30-50 fs pulses, like those produced at currently operating facilities, should not yet be ruled out. The theory presented opens up new experimental avenues to measure the impact of damage on single-particle diffraction, which is needed to test damage models and to identify optimal imaging conditions.

No MeSH data available.


Related in: MedlinePlus

Maximum signal-to-noise ratios with and without shot noise for a resolution of 0.15 nm for 8 keV photon energy, 100 × 100 nm spot size and constant pulse energy of 2 mJ.
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fig4: Maximum signal-to-noise ratios with and without shot noise for a resolution of 0.15 nm for 8 keV photon energy, 100 × 100 nm spot size and constant pulse energy of 2 mJ.

Mentions: The results are interesting when there is an experimental trade-off between pulse duration and pulse energy. For example, the Linac Coherent Light Source (LCLS, Menlo Park, California, USA) can produce 2 mJ pulses with pulse durations of 30–50 fs for hard X-rays (Emma et al., 2010 ▸). Pulses shorter than 5 fs can be produced by the LCLS using a low-charge method or a slotted-foil method, but at the expense of around a factor of ten in pulse energy. Given such a choice, the analysis presented here suggests that the gain in signal from a longer pulse with higher pulse energy compensates for the increase in damage. We note, though, that this conclusion only applies to spatially uncorrelated damage processes like ionization and ion diffusion (not a Coulomb explosion). Fig. 4 ▸ shows that SNRND(q) and SNRD(q) have a weak dependence on pulse duration at constant pulse energy. This suggests that maximizing pulse energy has a greater influence on the success of single-molecule imaging than pulse duration with respect to the spatially uncorrelated damage mechanisms considered here.


Single-molecule imaging with longer X-ray laser pulses.

Martin AV, Corso JK, Caleman C, Timneanu N, Quiney HM - IUCrJ (2015)

Maximum signal-to-noise ratios with and without shot noise for a resolution of 0.15 nm for 8 keV photon energy, 100 × 100 nm spot size and constant pulse energy of 2 mJ.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645111&req=5

fig4: Maximum signal-to-noise ratios with and without shot noise for a resolution of 0.15 nm for 8 keV photon energy, 100 × 100 nm spot size and constant pulse energy of 2 mJ.
Mentions: The results are interesting when there is an experimental trade-off between pulse duration and pulse energy. For example, the Linac Coherent Light Source (LCLS, Menlo Park, California, USA) can produce 2 mJ pulses with pulse durations of 30–50 fs for hard X-rays (Emma et al., 2010 ▸). Pulses shorter than 5 fs can be produced by the LCLS using a low-charge method or a slotted-foil method, but at the expense of around a factor of ten in pulse energy. Given such a choice, the analysis presented here suggests that the gain in signal from a longer pulse with higher pulse energy compensates for the increase in damage. We note, though, that this conclusion only applies to spatially uncorrelated damage processes like ionization and ion diffusion (not a Coulomb explosion). Fig. 4 ▸ shows that SNRND(q) and SNRD(q) have a weak dependence on pulse duration at constant pulse energy. This suggests that maximizing pulse energy has a greater influence on the success of single-molecule imaging than pulse duration with respect to the spatially uncorrelated damage mechanisms considered here.

Bottom Line: One of the key reasons for this success is the 'self-gating' pulse effect, whereby the X-ray laser pulses do not need to outrun all radiation damage processes.As a result, serial femtosecond crystallography does not need to be performed with pulses as short as 5-10 fs, but can succeed for pulses 50-100 fs in duration.The results suggest that sub-nanometre single-molecule imaging with 30-50 fs pulses, like those produced at currently operating facilities, should not yet be ruled out.

View Article: PubMed Central - HTML - PubMed

Affiliation: ARC Centre of Excellence for Advanced Molecular Imaging, School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia.

ABSTRACT
During the last five years, serial femtosecond crystallography using X-ray laser pulses has been developed into a powerful technique for determining the atomic structures of protein molecules from micrometre- and sub-micrometre-sized crystals. One of the key reasons for this success is the 'self-gating' pulse effect, whereby the X-ray laser pulses do not need to outrun all radiation damage processes. Instead, X-ray-induced damage terminates the Bragg diffraction prior to the pulse completing its passage through the sample, as if the Bragg diffraction were generated by a shorter pulse of equal intensity. As a result, serial femtosecond crystallography does not need to be performed with pulses as short as 5-10 fs, but can succeed for pulses 50-100 fs in duration. It is shown here that a similar gating effect applies to single-molecule diffraction with respect to spatially uncorrelated damage processes like ionization and ion diffusion. The effect is clearly seen in calculations of the diffraction contrast, by calculating the diffraction of the average structure separately to the diffraction from statistical fluctuations of the structure due to damage ('damage noise'). The results suggest that sub-nanometre single-molecule imaging with 30-50 fs pulses, like those produced at currently operating facilities, should not yet be ruled out. The theory presented opens up new experimental avenues to measure the impact of damage on single-particle diffraction, which is needed to test damage models and to identify optimal imaging conditions.

No MeSH data available.


Related in: MedlinePlus