Generation and detection of sinusoidal ultrasonic waves in the GHz-THz frequency rangeReport as inadecuate

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* Corresponding author 1 LPEC - Laboratoire de physique de l-état condensé 2 LAUM - Laboratoire d-acoustique de l-université du Maine

Abstract : Through a sinusoidal thermo-modulation of a thin metallic film deposited on a substrate, monochromatic acoustic waves can be generated in the substrate Damen, PRL 1995. Two interfering tunable lasers are used to induce a thermo-modulation at a frequency equal to the lasers beating frequency. Thus, the generated ultrasonic waves can be continuously tuned from 0 Hz up to the THz range by tuning the optical frequency of each pump laser. For the detection of the sinusoidal acoustic waves, an additional CW laser is used as a probe, which interacts with the laser-generated acoustic beam. The detection of the weak perturbation of the probe beam intensity induced by the acoustic beam requires a particular modulation of the pump lasers. We describe the experiments, which demonstrate that the detection of sinusoidal acoustic waves at frequencies in the GHz-THz range is possible. With a precise control of the optical frequency of both pump lasers, it becomes feasible to generate monochromatic acoustic waves with a very narrow line-width, typically less than one MHz. Ultrasound spectroscopy with high resolution is achievable using such monochromatic acoustic waves. This technique would be beneficial for the study of nano-resonators with very high-quality factors, such as nano-membranes and nano-rods.

Keywords : laser ultrasonics acoustic spectroscopy THz acoustic waves

Author: Denis Mounier - Tomasz Nowak Jean-Marc Breteau Gwenäelle Vaudel Thomas Pezeril - Pascal Picart - Pascal Ruello Vitaly Gusev



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