Key points: TG in optical range has been used to study coherent phonons and thermal transport

1. X-ray four-wave mixing: Transient grating measurements of nano-scale thermo-elastic responses F. Hofmann, K.A. Nelson • Key points: • TG in optical range has been used to study coherent phonons and thermal transport • To move to nano-scale need to reduce grating period and hence the wavelength • LCLS provides unique opportunity • –> coherence and time resolution • Experimental requirements • –> split and delay of pump and probe • –> generation of overlapping beams • Generalized non-linear X-ray spectroscopy Transient grating Transient grating generation Johnson et al. J. Appl. Phys. 110, 113513 (2011) Coherent phonons & thermal grating decay X-ray pump-probe splitting sample x-ray gratings signal Ti film on Si substrate, 0.76μm grating period Rogers et al.Annu. Rev. Mater. Sci. 30:117–57 (2000) Decane with alumina nanoparticles Schmidt et al. J. App. Phys. 103, 083529 2008 Heilmann et al. Optics Express 16, 8658 (2008) Roseker et al. Optics Letters 34 (12) 2009