Material Science, Chemistry, and Physics: Time-Resolved X-ray Scattering

Since its foundation, BioCARS has served time-resolved macromolecular crystallography community at the Advanced Photon Source. A recent upgrade of our 14-ID beamline increased the X-ray flux density by a factor of 100, improved pump-probe time-resolution to 100 ps, enabled us to use the widely-available 24-bunch mode of operation of the APS, and thus allows us to conduct time-resolved experiments for about 4000 hours per year (Graber et al., 2011). We also expanded our scientific reach beyond macromolecular crystallography to biological SAXS/WAXS. In addition, our upgraded technical capabilities have proved to be suitable to and attracted the attention of the time-resolved X-ray scattering community in the physical sciences.

Physical sciences user projects successfully conducted at 14-ID include photo-switching dynamics in spin-crossover molecular complexes (Collet et al, 2012), charge transfer and excited state structures in small molecules (Makal et al, 2012), X-ray pump optical probe cross-correlation study of GaAs (Durbin et al., 2012), time-resolved diffuse scattering to study the structural dynamics of photo-excited bismuth (Chen et al., 2013) etc.

14-ID capabilities for time-resolved science:

  • Picosecond and nanosecond lasers synchronized with X-ray pulses are available for pump-probe experiments (< 5ps rms timing jitter)
  • Single 100ps X-ray pulse isolation by an X-ray shutter system allows pump-probe time delays of arbitrary length (from 100 ps to ms, and longer)
  • 100ps pulse isolation is possible in both hybrid and 24-bunch modes of the APS storage ring
  • Both polychromatic (pink and white) and pulsed monochromatic (7-20 keV) X-ray beams are available
  • High X-ray flux per single 100ps X-ray pulse: 3 X 1010 photons/pulse (with two in-line undulators, polychromatic pulses, hybrid mode of the APS storage ring)
  • Two in-line undulators, U23 and U27; possible to modify the X-ray spectrum by offsetting the energies of the first harmonic for two undulators and/or tapering the undulator gaps
  • Pump-probe repetition rate: 40Hz to 1KHz
  • Detector readout rate: 10-100Hz with the new large area, high speed readout Rayonix detector (to be installed in March 2014)
  • Focusing: 20 (v) X 20 (h) µm2

Chen, J., Trigo, M., Fahy, S., Murray, E. D., Sheu, Y. M., Graber, T., Henning, R., Chien, Y. J., Uher, C., and Reis, D. A. (2013) Time- and momentum-resolved probe of heat transport in photo-excited bismuth. Applied Physics Letters 102, 181903.

Collet, E., Moisan, N., Baldé, C., Bertoni, R., Trzop, E., Laulhé, C., Lorenc, M., Servol, M., Cailleau, H., Tissot, A., Boillot, M.-L., Graber, T., Henning, R., Coppens, P., and Cointe, M. B.-L. (2012) Ultrafast spin-state photoswitching in a crystal and slower consecutive processes investigated by femtosecond optical spectroscopy and picosecond X-ray diffraction. Phys Chem Chem Phys 14, 6185–6192.

Durbin, S. M., Clevenger, T., Graber, T., and Henning, R. (2012) X-ray pump optical probe cross-correlation study of GaAs. Nat Photon 6, 111–114.

Graber, T., Anderson, S., Brewer, H., Chen, Y.-S., Cho, H. S., Dashdorj, N., Henning, R. W., Kosheleva, I., Macha, G., Meron, M., Pahl, R., Ren, Z., Ruan, S., Schotte, F., Šrajer, V., Viccaro, P. J., Westferro, F., Anfinrud, P., and Moffat, K. (2011) BioCARS: a synchrotron resource for time-resolved X-ray science. J Synchrotron Rad 18, 658–670.

Makal, A., Benedict, J., Trzop, E., Sokolow, J., Fournier, B., Chen, Y., Kalinowski, J. A., Graber, T., Henning, R., and Coppens, P. (2012) Restricted Photochemistry in the Molecular Solid State: Structural Changes on Photoexcitation of Cu(I) Phenanthroline Metal-to-Ligand Charge Transfer (MLCT) Complexes by Time-Resolved Diffraction. J Phys Chem A 116, 3359–3365.

Transmission of GaAs at 860 nm versus time after X-ray pump pulse

Data points are normalized to the transmitted intensity before X-ray excitation and are the average of 100 shots. Error bars are the standard deviation of 100 shots and are largely due to laser/X-ray pulse timing jitter. Dashed curve: Gaussian time profile of X-ray pulses. Solid curve: integral, which matches data at the transition region. Inset (top): scattering geometry, with GaAs surface at the intersection of the X-ray and laser beams. Inset (bottom): transmission at longer times, fit to an exponential decay with a lifetime of 1.1 ns. S.M. Durbin, T. Clevenger, T. Graber, R. Henning X-ray pump optical probe cross-correlation study of GaAs Nat. Photonics 6, 111-114 (2012)