Mechanisms of pulsed photoacoustic generation

Abstract

The mechanisms by which ultrasonic transients may be generated by pulsed laser irradiation are reviewed, with particular reference to the wave forms resulting in both fluid and solid media. Specilic examples of experimental results are presented that demonstrate that a pulsed ultraviolet source is a convenient means for ultrasonic generation in both liquids and solids.Une revue est faitc des micanismes par lesquels des ondes ultrasoniqucs transitoires peuvent ttre gCnCrkes par irradiation laser pulsie, avec une attention particulikre portie aux formes d'ondes risultantes dans les milieux fluides et solides. Des exemples spicifiques de rCsultats expirimentaux sont prksentis, qui dimontrent qu'une source ultra-violette pulsie est un moyen pratique de g6nCration d'ultra-sons ii la fois dans les liquides et les solides.[Traduit par la revue]

Ultrasound generated by a femtosecond and a picosecond laser pulse near the ablation threshold

“…The transition between these two regimes occurs at the ablation threshold, which is usually defined in terms of fluence, i.e., the incident laser energy divided by the surface containing this energy. 3,4 This threshold varies as a function of the laser-pulse duration. 31 The ablation thresholds of Al samples used in the present ultrasound experiments were determined by measuring the broadband white light emitted from the sample surface, indicative of plasma generation and significant ejection of matter.…”

Long Cavity Laser Excitation and Digital Filtering of Narrowband Ultrasound for Enhanced Signal-to-Noise Ratio

“…First, the multiple pulse signal alone was extracted from the raw waveform and processed with a Fast Fourier Transform (FFT) algorithm to produce the numerator in Eq. (2). Aseparate FFT on the raw waveform (containing both signal and noise) then yielded the power spectrum in the denominator in Eq.…”

“…Aseparate FFT on the raw waveform (containing both signal and noise) then yielded the power spectrum in the denominator in Eq. (2).…”

“…Ultrasonic signals are typically generated by pulsed laser irradiation of the sample surface [2] and detected by some sort of heterodyne, Fabry-Perot, or pathstabilized Michelson interferometer [3]. While optical methods for generation and detection of ultra sound have performed quite satisfactorily under controlled laboratory conditions, similar success in more demanding industrial environments has proven elusive because the optical techniques suffer limitations with regard to generation efficiency and detection sensitivity.…”

Photoacoustic monitoring of changes in the blood circulation

“…In that case, the shape of the transient of a spherical or a cylindrical source is a bipolar signal. 1,2 The PA technique can be used to determine tissue characteristics 3 or to construct tomographic images of biological tissue. 4 The main advantage of it, compared to the existing optical imaging techniques ͑transillumination, optical coherence tomography, confocal microscopy, etc.͒, is that it does not suffer from the strong scattering of light in turbid media such as biological tissue.…”