| Autor: |
Paul C. M. Planken, G. de Haan, T. J. van den Hooven |
| Přispěvatelé: |
WZI (IoP, FNWI), ARCNL (WZI, IoP, FNWI) |
| Rok vydání: |
2021 |
| Předmět: |
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| Zdroj: |
Optics Express, 29(20), 32051-32067. The Optical Society |
| ISSN: |
1094-4087 |
| Popis: |
We report on the time-dependent optical diffraction from ultra-high frequency laser-induced acoustic waves in thin layers of ruthenium deposited on glass substrates. We show that the thermo-optic and strain-optic effects dominate the optical response of Ru layers to a traveling longitudinal strain wave. In addition, we show the generation and detection of acoustic waves with a central frequency ranging from 130 GHz to 750 GHz on ultra-thin layers with thicknesses in the range of 1.2 - 20 nm. For these ultra-thin layers we measure a strong dependency of the speed of sound on the layer thickness and, thus, the frequency. This frequency-dependent speed of sound results in a frequency-dependent acoustic impedance mismatch between the ruthenium and the glass substrate, leading to a faster decay of the measured signals for increasing frequency. Furthermore, for these extremely high-frequency oscillations, we find that the frequency and phase remain constant for times longer than about 2 ps after optical excitation. Back extrapolation of the acquired acoustic signals to t = 0 gives a starting phase of −π/2. As this seems unlikely, we interpret this as an indication of possible dynamic changes in the phase/frequency of the acoustic wave in the first 2 ps after excitation. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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