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Generation and detection of quasi-monochromatic sound waves

Quasi-monochromatic strain waves can be detected by Ultrafast X-Ray Diffraction (UXRD) as sidebands of the substrate reflection. Depending on the sensitivity of the experiment, several higher-order peaks can be detected. The propagating waves are either generated by optical excitation of a transducer with multiple pump pulses or by the excitation of a superlattice with a single pulse. In particular, this method allows for the generation of coherent phonons with different frequencies. UXRD is a direct probe of the phonon lifetime in different wavelength and temperature regimes. It also allows for the detection of nonlinear transport phenomena, e.g. frequency conversion of the propagating phonons.

enlarged view

Photo-excited strain wave and subsequent propagation in the substrate