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Extracted oscillations obtained from the transducers with 600 nm period for different distances between pump and probe spot. For better comparability the traces are offset and shifted so that the centers of the gaussian envelopes of the measured sine waves coincide.
Spectra of the gratings with periods of 600, 400, 300, and 200 nm. Pump and probe spot were overlapping. Relevant peaks are marked (see text). The first peak corresponds to the RSAW and second peak to the LLSAW. The LLSAW peak is not visible in the last spectrum due to its small intensity.
Spectrum of the grating with a period of 100 nm. Pump and probe are overlapping. Relevant peaks are marked and explained in the text. Note that the frequency scale differs from the other spectra presented in Fig. 2. The large peak in the center of the spectra is caused by the Brillouin mode and only visible when pump and probe overlap.
Frequency over nominal grating period diagram of the measured dominant modes. Measured modes are plotted next to the results of finite element simulations for a large number of different pitches.
Decay of the RSAW and LLSAW for the 300 nm period. Each point corresponds to the amplitude of the mode measured with a certain distance between pump and probe in the corresponding spectrum (spectra not shown). Amplitudes are normalized to the peaks in the spectra with overlapping pump and probe spot to better compare the different decay lengths of both modes. Distance between pump and probe was measured by imaging the surface with both spots visible. The fits are exponential decay functions.
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