Abstract
The spectrum of laser-generated acoustic phonons in indium antimonide coated with a thin nickel film has been studied using time-resolved x-ray diffraction. Strain pulses that can be considered to be built up from coherent phonons were generated in the nickel film by absorption of short laser pulses. Acoustic reflections at the Ni–InSb interface leads to interference that strongly modifies the resulting phonon spectrum. The study was performed with high momentum transfer resolution together with high time resolution. This was achieved by using a third-generation synchrotron radiation source that provided a high-brightness beam and an ultrafast x-ray streak camera to obtain a temporal resolution of 10 ps. We also carried out simulations, using commercial finite element software packages and on-line dynamic diffraction tools. Using these tools, it is possible to calculate the time-resolved x-ray reflectivity from these complicated strain shapes. The acoustic pulses have a peak strain amplitude close to 1%, and we investigated the possibility to use this device as an x-ray switch. At a bright source optimized for hard x-ray generation, the low reflectivity may be an acceptable trade-off to obtain a pulse duration that is more than an order of magnitude shorter.
Highlights
When a short laser pulse impinges on the surface of a material, the resulting heating and thermal expansion generate an acoustic strain pulse.1,2 This strain pulse is built up by a range of acoustic phonon modes that can be studied individually using time-resolved x-ray diffraction (TRXD).3,4 Different strategies have been devised to modify and control the phonon spectrum
The spectrum of laser-generated acoustic phonons in indium antimonide coated with a thin nickel film has been studied using time-resolved x-ray diffraction
Strain pulses that can be considered to be built up from coherent phonons were generated in the nickel film by absorption of short laser pulses
Summary
When a short laser pulse impinges on the surface of a material, the resulting heating and thermal expansion generate an acoustic strain pulse. This strain pulse is built up by a range of acoustic phonon modes that can be studied individually using time-resolved x-ray diffraction (TRXD). Different strategies have been devised to modify and control the phonon spectrum. When a short laser pulse impinges on the surface of a material, the resulting heating and thermal expansion generate an acoustic strain pulse.1,2 This strain pulse is built up by a range of acoustic phonon modes that can be studied individually using time-resolved x-ray diffraction (TRXD).. There is a need to control the phonon spectrum for two main reasons: first to be able to observe and diagnose objects “buried” in materials and second to create a simple device that can act as a fast x-ray switch.. There is a need to control the phonon spectrum for two main reasons: first to be able to observe and diagnose objects “buried” in materials and second to create a simple device that can act as a fast x-ray switch.10,11 Such a switch could be used to create short x-ray pulses at a storage ring without having to perturb the electrons in the storage ring There is a need to control the phonon spectrum for two main reasons: first to be able to observe and diagnose objects “buried” in materials and second to create a simple device that can act as a fast x-ray switch. Such a switch could be used to create short x-ray pulses at a storage ring without having to perturb the electrons in the storage ring
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