Berkeley Lab


Laser seeding of the storage ring microbunching instability for high-power coherent terahertz radiation

J. M. Byrd, Z. Hao, M. C. Martin, D.S. Robin, F. Sannibale, R.W. Schoenlein, A. A. Zholents, M.S. Zolotorev
Phys. Rev. Lett. 97, 074802, (2006) (LBNL-60002)

We report the first observation of laser seeding of the storage-ringmicrobunching instability. Above a threshold bunch current, the interaction ofthe beam and its radiation results in a coherent instability,observed as a series of stochastic bursts of coherent synchrotronradiation (CSR) at terahertz frequencies initiated by fluctuations in thebeam density. We have observed that this effect can beseeded by imprinting an initial density modulation on the beamby means of laser “slicing.” In such a situation, mostof the bursts of CSR become synchronous with the pulsesof the modulating laser and their average intensity scales exponentiallywith the current per bunch. We present detailed experimental observationsof the seeding effect and a model of the phenomenon.This seeding mechanism also creates potential applications as a high-powersource of CSR at terahertz frequencies.

Picosecond x-ray absorption spectroscopy of photochemical transient species in solution

M. Khalil, M.A. Marcus, A.L. Smeigh, J.K. McCusker, H.H.W. Chong, and R.W. Schoenlein
Ultrafast Phenomena XV, Springer Series in Chemical Physics 88, 722, P. Corkum, D. Jonas, D. Miller, A.M. Weiner, Eds., Springer-Verlag, (2007)

Ultrafast Phenomena XV presents the latest advances in ultrafast science, including both ultrafast optical technology and the study of ultrafast phenomena. It covers picosecond, femtosecond, and attosecond processes relevant to applications in physics, chemistry, biology, and engineering. Ultrafast technology has a profound impact in a wide range of applications, among them biomedical imaging, chemical dynamics, frequency standards, materials processing, and ultrahigh-speed communications. This book summarizes the results presented at the 15th International Conference on Ultrafast Phenomena and provides an up-to-date view of this important and rapidly advancing field.

Picosecond x-ray absorption spectroscopy of a photoinduced iron(II) spin crossover reaction in solution

M. Khalil, M.A. Marcus, A.L. Smeigh, J.K. McCusker, H.H.W. Chong, and R.W. Schoenlein
J. Phys. Chem. A 110, pp. 38-44 (2006). (LBNL-58982)

n this study, we perform steady-state and time-resolved X-ray absorption spectroscopy (XAS) on the iron K-edge of [Fe(tren(py)3)](PF6)2 dissolved in acetonitrile solution. Static XAS measurements on the low-spin parent compound and its high-spin analogue, [Fe(tren(6-Me-py)3)](PF6)2, reveal distinct spectroscopic signatures for the two spin states in the X-ray absorption near-edge structure (XANES) and in the X-ray absorption fine structure (EXAFS). For the time-resolved studies, 100 fs, 400 nm pump pulses initiate a charge-transfer transition in the low-spin complex. The subsequent electronic and geometric changes associated with the formation of the high-spin excited state are probed with 70 ps, 7.1 keV, tunable X-ray pulses derived from the Advanced Light Source (ALS). Modeling of the transient XAS data reveals that the average iron-nitrogen (Fe-N) bond is lengthened by 0.21 ± 0.03 Å in the high-spin excited state relative to the ground state within 70 ps. This structural modification causes a change in the metal-ligand interactions as reflected by the altered density of states of the unoccupied metal orbitals. Our results constitute the first direct measurements of the dynamic atomic and electronic structural rearrangements occurring during a photoinduced FeII spin crossover reaction in solution via picosecond X-ray absorption spectroscopy.

A setup for ultrafast time-resolved x-ray absorption spectroscopy

Thursday, 01 January 2004

M. Saes, C. Bressler, F. van Mourik, W. Gawelda, M. Kaiser, M. Chergui, D. Grolimund, R. Abela, T.E. Glover, P.A. Heimann, R.W. Schoenlein, S.L. Johnson, A.M. Lindenberg, and R.W. Falcone
Rev. Sci. Inst. 75, pp. 24-30 (2004) (LBNL-55297) Wepresent a setup which allows the measurement of time-resolved x-rayabsorption spectra with picosecond temporal resolution on liquid samples atthe Advanced Light Source at Lawrence Berkeley National Laboratories. Thetemporal resolution is limited by the pulse width of thesynchrotron source. We characterize the different sources of noise thatlimit the experiment and present a single-pulse detection scheme. ©2004American Institute of Physics.

Generation of femtosecond X-ray pulses via laser-electron beam interaction

Saturday, 01 July 2000

R. W. Schoenlein, S. Chattopadhyay, H. H. W. Chong, T. E. Glover, P. A. Heimann, W.P. Leemans, C. V. Shank, A. Zholents, and M. Zolotorev
Appl. Phys. B 71, 1-10 (2000) The generation of femtosecond X-ray pulses will have important scientific applications by enabling the direct measurement of atomic motion and structural dynamics in condensed matter on the fundamental time scale of a vibrational period. Interaction of femtosecond laser pulses with relativistic electron beams is an effective approach to generating femtosecond pulses of X-rays. In this paper we present recent results from proof-of-principle experiments in which 300 fs pulses are generated from a synchrotron storage ring by using an ultrashort optical pulse to create femtosecond time structure on the stored electron bunch. A previously demonstrated approach for generating femtosecond X-rays via Thomson scattering between terawatt laser pulses and relativistic electrons is reviewed and compared with storage-ring based schemes.

Femtosecond x-rays from a synchrotron: A new tool for ultrafast time-resolved x-ray spectroscopy

Friday, 24 March 2000

R. W. Schoenlein, S. Chattopadhyay, H. H. W. Chong, T. E. Glover, P. A. Heimann, C. V. Shank, A. Zholents, and M. Zolotorev
Science 287, 2237-2240 (2000)  Femtosecond synchrotron pulses were generated directly from an electron storage ring. An ultrashort laser pulse was used to modulate the energy of electrons within a 100-femtosecond slice of the stored 30-picosecond electron bunch. The energy-modulated electrons were spatially separated from the long bunch and used to generate ~300-femtosecond synchrotron pulses at a bend-magnet beamline, with a spectral range from infrared to x-ray wavelengths. The same technique can be used to generate ~100-femtosecond x-ray pulses of substantially higher flux and brightness with an undulator. Such synchrotron-based femtosecond x-ray sources offer the possibility of applying x-ray techniques on an ultrafast time scale to investigate structural dynamics in condensed matter.