Picosecond Laser Ultrasonics: an interesting technique for imaging and mechanical characterization

CIC nanoGUNE Seminars

Speaker

Samuel Raetz
Guest Researcher at CIC nanoGUNE, University of Le Mans, France

When

2023/11/06
11:00

Place

nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian

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In this seminar, I will briefly expose the fundamentals of picosecond laser ultrasonics and provide recent examples of its applications in our research group at Le Mans Université (specifically, at the Laboratoire d’Acoustique de l’Université du Mans - LAUM). This technique operates on a pump-probe principle. Initially, an ultrashort laser pulse (the "pump") is employed to generate coherent acoustic pulses. Subsequently, a second laser pulse, ultrafast and time-delayed (the "probe"), is used to monitor these acoustic waves. The extent to which the sample interacts with the probe light wavelength determines the detection of acoustic pulses. If the sample absorbs this wavelength, the detection is confined to the proximity of the absorbing surface. However, when the sample is transparent to the probe light wavelength, it offers the opportunity to trace the acoustic pulses throughout their propagation path, enabled by the photoelastic effect. This capability allows the depth profiling of materials, providing both mechanical and optical contrast with axial resolution defined by the acoustic pulse length, typically sub-optical.

My talk will primarily focus on this later application of picosecond laser ultrasonics known as time-domain Brillouin scattering, and especially its application in three-dimensional imaging of polycrystalline materials under high pressure and the characterization of their mechanical properties. Additionally, I will touch upon the generation and detection of surface acoustic waves within the frame of picosecond laser ultrasonics, shedding light on the purpose of my visit to your laboratory.