Pseudo-random modulation of a laser diode for generating ultrasonic longitudinal waves

Eric, I Madaras; Robert, F.

doi:10.1063/1.1306065

Cited by 7 publications

(1 citation statement)

References 9 publications

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“…Murray 336 that a sample can be excited over long time scales. Two general modulation techniques have been employed: broadband-coded modulation [34,35], and narrowband sinusoidal modulation [36 -38]. In broadband modulation, the laser output is modulated with, for example, a chirp or pseudo-random sequence.…”

Section: Introductionmentioning

confidence: 99%

Frequency domain photoacoustics using intensity-modulated laser sources

Balogun

Murray

2011

Nondestructive Testing and Evaluation

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In this paper, we present an overview of research in the area of narrow-bandwidth generation and detection of ultrasound using a technique referred to as frequency domain photoacoustics. An intensity-modulated continuous wave laser is used for narrowband ultrasound generation, and an interferometer coupled to a radio frequency lock-in amplifier is used for detection. Excellent sensitivity is achieved using sinusoidal modulation of the excitation laser over long time scales, thereby focusing the acoustic energy at the excitation frequency. We describe an experimental approach for the direct detection of narrowband signals at the ultrasound excitation frequency, and a superheterodyne technique in which the signal is optically down-converted to a low and fixed intermediate frequency prior to detection. Two approaches for materials characterisation using frequency domain photoacoustic measurements are presented. In the first approach, the modulation frequency of the excitation laser is scanned over the bandwidth of interest, and a transient sample response is constructed from the frequency-domain data. Ultrasound arrivals that are separated in the time domain can then be time gated for further analysis. In the second approach, the modulation frequency of the excitation laser is fixed, but the source-to-receiver distance is varied. The spatial frequencies of the ultrasound modes generated by the laser are detected by analysing the spatial variation of the phase, allowing for the velocity of each mode at a given frequency to be determined. Experimental measurements in thin films, plates and nanomechanical structures are presented.

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Section: Introductionmentioning

confidence: 99%

Frequency domain photoacoustics using intensity-modulated laser sources

Balogun

Murray

2011

Nondestructive Testing and Evaluation

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Ultrasonic guided waves for aging wire insulation assessment

Robert

Eric

2002

AIP Conference Proceedings

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Environmentally aged wire insulation can become brittle and crack and thus expose the underlying conductive wire to the potential for short circuits and fire. The feasibility of using ultrasonic guided waves to measure insulation condition was examined. First a simple model to study guided wave propagation in a bare and thin plastic coated wire was examined and then some aviation grade wire samples that had been heat-damaged. Initial measurements indicate that ultrasonic guided wave velocity can be used to monitor insulation stiffness.

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A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients

Balogun

Murray

2006

Journal of Applied Physics

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A high-sensitivity frequency domain laser based ultrasonic system is presented which uses a low power, amplitude modulated continuous wave (cw) laser source for acoustic wave generation. The acoustic signals are detected using a path stabilized Michelson interferometer coupled to a rf lock-in amplifier. The modulation frequency of the generation laser is scanned over the bandwidth of interest, and transient acoustic signals are reconstructed from the frequency domain data. The effects of measurement frequency resolution, bandwidth, and time domain aliasing on the reconstructed transient response are discussed. Experimental results on thin plates, where diffuse acoustic wave fields lasting several hundred microseconds are seen as a result of multiple reflections off of sample boundaries, demonstrate that the time domain signal can be unambiguously reconstructed through appropriate selection of frequency resolution. Time domain reconstructions of acoustic signals over a bandwidth of 200MHz demonstrate the utility of the approach for acoustic microscopy; individual acoustic transients can be detected with extremely high signal to noise ratio and time gated for analysis.

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Pseudo-random modulation of a laser diode for generating ultrasonic longitudinal waves

Cited by 7 publications

References 9 publications

Frequency domain photoacoustics using intensity-modulated laser sources

Frequency domain photoacoustics using intensity-modulated laser sources

Ultrasonic guided waves for aging wire insulation assessment

A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients

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