NEH 2.1 RIXS‎ > ‎

Science Drivers

The combination of exceptionally high flux of near-monochromatic photons, far exceeding that at current state-of-the-art instruments, delivered in the form transform-limited femtosecond X-ray pulses, will make the RIXS Instrument at LCLS-II one with transformational capabilities.  It will significantly expand the parameter space covered by this technique as it will allow one to study elementary excitations in samples placed out of equilibrium, e.g.  via the application of photo-excitation pulse, magnetic field, etc.  The major thrusts are:

  • Time-resolved RIXS:
    • A unique aspect of the RIXS instrument enabled by LCLS-II is the capability of performing time-resolved measurements with high energy resolution (e.g., 100 fs correspond to 18 meV at the Fourier-transform limit) to study the dynamics of photo-induced non-equilibrium states.  Upon photo-excitation, one can readily  probe  the  temporal  evolution  of  elementary  excitations.   It  is  possible  to  use ultrafast  pulses spanning the visible-to-THz regimes to induce coherent collective excitations and/or to temporally alter the strongly intertwined degrees of freedom to create new states that are inaccessible in thermal equilibrium.  These novel photo-induced phenomena are ultimately related to the mechanisms of emergent phenomena in equilibrium.
  • Ultrahigh Resolution RIXS:
    • Another potential of an RIXS instrument at LCLS-II is the possibility of performing ultrahigh resolution RIXS measurements that are rivaling and possibly beyond the capabilities of current synchrotron X-ray sources.  This is simply because the high-repetition rate and the narrow bandwidth of a seeded X-ray FEL at LCLS-II can deliver orders of magnitude higher photon flux in a narrow bandwidth than any synchrotron light source.
  • Non-equilibrium RIXS:
    • The  extremely  high  flux  will  allow  for  faster  and  much  more  complete  investigation  of  the  physical properties of correlated materials across the full the phase diagram, including when the system is out of equilibrium.  For example, the application of high magnetic fields is a crucial tool in studies of quantum magnetism and correlated electron systems.  Hence,  pulsed fields with X-rays would open the door to studying  normal  state  excitations  at  low  temperatures  in  the  cleanest  systems.
  • Stimulated RIXS:
    • The extremely high intensity of FEL pulses is very promising for studying non-linear effects in the x-ray range.  Here we will take advantage of the capability to generate ultrashort few-femtosecond pulses, coupled with small spot size on the sample and a flexible geometry of the RIXS spectrometer.