Time-domain Brillouin scattering theory for probe light and acoustic beams propagating at an angle and acousto-optic interaction at material interfaces

A theory has been developed to interpret time-domain Brillouin scattering (TDBS) experiments involving coherent acoustic pulse (CAP) and light pulse beams propagating at an angle to each other. It predicts the influence of the directivity pattern of their acousto-optic interaction on TDBS signals wh...

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Bibliographic Details
Published in:Photoacoustics (Munich) 2023-10, Vol.33 (C), p.100563, Article 100563
Main Authors: Gusev, Vitalyi E., Thréard, Théo, Hurley, David H., Raetz, Samuel
Format: Article
Language:English
Subjects:
Acoustics
Engineering
Instruments & Instrumentation
Material interface
Non-collinear interaction
Picosecond laser ultrasonics
Radiology, Nuclear Medicine & Medical Imaging
Time-domain Brillouin scattering
Ultrafast photoacoustics
VSI:Ultrafast Photoacoustics
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Summary:A theory has been developed to interpret time-domain Brillouin scattering (TDBS) experiments involving coherent acoustic pulse (CAP) and light pulse beams propagating at an angle to each other. It predicts the influence of the directivity pattern of their acousto-optic interaction on TDBS signals when heterodyne detection of acoustically scattered light is in backward direction to incident light. The theory reveals relationships between the carrier frequency, amplitude and duration of acoustically induced ”wave packets” in light transient reflectivity signals, and factors such as CAP duration, widths of light and sound beams, and their interaction angle. It describes the transient dynamics of these wave packets when the light and CAP encounter material interfaces, and how the light scattering by the incident CAP transforms into scattering by the reflected and transmitted CAPs. The theory suggests that single-point TDBS experiments can determine not only depth positions of buried interfaces but also their local inclinations/orientations. [Display omitted] •We propose a new analytical theory for time-domain Brillouin scattering (TDBS).•Non-collinear interaction of Gaussian probe light and acoustic beams is analyzed.•Away from an interface, the TDBS signal shows a Gaussian wave packet form.•At interfaces, incident, reflected & refracted acoustic pulses contribute uniquely.•We provide guidance for theory extensions and experimental demonstrations.
ISSN:2213-5979
2213-5979
DOI:10.1016/j.pacs.2023.100563