Hadamard multiplexing in laser ultrasonics

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DOIResolve DOI: http://doi.org/10.1364/OE.20.025798
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Journal titleOptics Express
Pages2579825816; # of pages: 19
SubjectHadamard multiplexing; Laser intensities; Laser ultrasonics; Non-contact ultrasonic inspection; Pulse echoes; Shot-noise level; Signaltonoise ratio (SNR); Spatial intensity distribution; Surface damages; Synthetic aperture focusing techniques; Chemical detection; Detectors; Laser beams; Shot noise; Signal detection; Signal to noise ratio
AbstractIn state-of-the-art laser ultrasonics (LU), the signal-to-noise ratio (SNR) is limited by the shot noise of the detected laser radiation. Further improving the SNR then requires averaging multiple signals or increasing generation and/or detection laser intensities. The former strategy is time consuming and the latter leads to surface damages. For signal-independent limiting noises, Hadamard multiplexing increases the SNR by averaging multiple signals in parallel using a single detector. Here we consider the use of Hadamard multiplexing in LU for the non-contact ultrasonic inspection of materials. By using 31 element Hadamard masks to modulate the spatial intensity distribution of the generation laser beam, the measured SNR is improved by a factor 2.8, in good agreement with the expected multiplexing or Fellgett advantage. In contrast to many other applications of Hadamard multiplexing, the SNR is improved for shot-noise-limited measurements since the shot noise level is independent of the signal in LU. The Hadamard multiplexing of the detection laser beam is also considered but can only lead to a throughput or Jacquinot advantage. However, for pulse-echo LU, the Hadamard multiplexing of both generation and detection laser beams allows using the synthetic aperture focusing technique (SAFT).
Publication date
AffiliationNational Research Council Canada; Energy, Mining and Environment
Peer reviewedYes
NRC numberNRC-EME-53217
NPARC number21270150
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Record identifier1e4b6963-fcf6-4392-af16-a95c1e21310e
Record created2014-01-06
Record modified2016-05-09
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