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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 23 — Nov. 5, 2012
  • pp: 25798–25816

Hadamard multiplexing in laser ultrasonics

Guy Rousseau and Alain Blouin  »View Author Affiliations

Optics Express, Vol. 20, Issue 23, pp. 25798-25816 (2012)

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In 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).

© 2012 OSA

OCIS Codes
(060.4230) Fiber optics and optical communications : Multiplexing
(110.7170) Imaging systems : Ultrasound
(120.0280) Instrumentation, measurement, and metrology : Remote sensing and sensors
(120.4290) Instrumentation, measurement, and metrology : Nondestructive testing
(280.3375) Remote sensing and sensors : Laser induced ultrasonics

ToC Category:
Instrumentation, Measurement, and Metrology

Original Manuscript: September 5, 2012
Revised Manuscript: October 17, 2012
Manuscript Accepted: October 18, 2012
Published: October 31, 2012

Guy Rousseau and Alain Blouin, "Hadamard multiplexing in laser ultrasonics," Opt. Express 20, 25798-25816 (2012)

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