Abstract
We use femtosecond extreme ultraviolet pulses derived from a free electron laser to excite and probe surface acoustic waves (SAWs) on the (001) surface of single crystal SrTiO3. SAWs are generated by a pair of 39.9 nm pulses crossed at the sample with the crossing angle defining the SAW wavelength at 84 nm. Detection of SAWs is performed via diffraction of a time-delayed 13.3 nm probe pulse by SAW-induced surface ripples. Despite the low reflectivity of the sample in the extreme ultraviolet range, the reflection mode detection is found to be efficient because of an increase in the diffraction efficiency for shorter wavelengths. We describe a methodology for extracting the SAW attenuation in the presence of a thermal grating, which is based on measuring the decay of oscillations at twice the SAW frequency. The proposed approach can be used to study ultrahigh frequency SAWs in a broad range of materials and will bridge the wave vector gap in surface phonon spectroscopy between Brillouin scattering and He atom scattering.
Highlights
This limitation can be circumvented by using subwavelength structures such as nanoscale arrays of metal lines[9,10,11,12] but that takes away a major advantage of the laser-based approach, i.e., the ability to generate and detect frequency-tunable SAWs in a non-contact and noninvasive manner without fabricating any transducer structures
We use femtosecond extreme ultraviolet pulses derived from a free electron laser to excite and probe surface acoustic waves (SAWs) on the (001) surface of single crystal SrTiO3
With the recent progress in free electron lasers (FELs) and high harmonic generation,[13] femtosecond sources operating in the extreme ultraviolet (EUV) and x-ray ranges have become available
Summary
G. Izzo,[5,6] C. Bonetti,[3,8] and K.
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