Alex gave a talk at the IEEE Ultrasonics Symposium in Washington, DC
Generation of acoustic waves by an extreme ultra violet free electron laser in a transient grating experiment
F. Bencivengaa, A. Cannizzog, F. Capotondia, R. Cucinic, R. A. Duncane, T. Feurerg, L. Fogliaa, T. Frazerh, H.-M. Freyg, J. Knoblochh, G. Knoppf, A. A. Mazneve, R. Mincigruccia, G. Monacod, K. A. Nelsone, E. Pedersolia, A. Simonciga, A. Vega-Flicki
aElettra-Sincrotrone Trieste, Basovizza, Italy.
bDepartment of Physics, University of Trieste, Trieste, Italy.
cIOM-CNR, Basovizza, Trieste, Italy
dDepartment of Physics, University of Trento, Povo (TN), Italy
eDepartment of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
fPaul Scherrer Institute, Villigen, Switzerland
gUniversity of Bern, Bern, Switzerland
hUniversity of Colorado, Boulder, CO, USA
iApplied Physics Department, CINVESTAV-Unidad Mérida, Mérida, Yucatán, Mexico
Background, Motivation and Objective
The use of lasers to generate acoustic waves revolutionized the field of ultrasound and enabled numerous key developments in both fundamental research and applications. In the past decade, remarkable progress has been achieved in developing coherent sources of radiation operating in the extreme ultraviolet (EUV) and x-ray ranges, such as free electron lasers, which already yielded many breakthroughs in different fields of science. We expect that the field of ultrasonics will also greatly benefit from the availability of coherent EUV and x-ray sources. So far, a number of studies explored the use of coherent EUV and x-ray radiation for detection of acoustic waves. In this report, we describe the first experiment on the generation of surface and bulk acoustic waves in the tens of GHz range by EUV light.
Statement of Contribution/Methods
We used the transient grating (TG) geometry in which two crossed excitation EUV pulses excite acoustic waves at a wavevector defined by the period of the EUV interference pattern. The experiments were performed at the DiProI beamline at the FERMI-Elettra light source facility in Trieste. The FERMI free electron laser provided femtosecond excitation pulses at a wavelength of 13.3 nm, which were crossed in the sample to generate both longitudinal and surface acoustic waves (SAWs) at a wavelength of 280 nm. The acoustic waves were detected via diffraction of a probe 400 nm laser pulse.
We have observed bulk and surface acoustic waves in a number of materials such as diamond, silicon, SiGe, BK-7 glass, and Bi4Ge3O12. In diamond, we generated SAWs at a frequency of 39 GHz, the highest SAW frequency ever produced without periodic structures. We will discuss the frequency mixing of SAWs and bulk longitudinal waves in the TG signal and probing different acoustic modes in reflection and transmission geometries. While the use of an optical probe limited the shortest achievable acoustic wavelength, the implementation of an EUV probe will permit the generation of bulk and surface acoustic waves at wavelengths down to 10 nm and below at frequencies up to 1 THz and above, creating an ultimate source of tunable GHz-THz frequency ultrasound without the need to fabricate any transducer structures on the sample.