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Input pulse duration effect on laser-induced underwater acoustic signals
Applied Optics
|June 18, 2021
Summary
Nanosecond laser-induced breakdown (LIB) generates stronger underwater acoustic signals (UASs) than picosecond LIB. Nanosecond pulses are more suitable for applications requiring robust acoustic impulses, both direct and reflected.
Area of Science:
- Physics
- Acoustics
- Laser-Plasma Interactions
Background:
- Laser-induced breakdown (LIB) in water generates acoustic waves.
- Understanding the characteristics of these underwater acoustic signals (UASs) is crucial for various applications.
- The influence of laser pulse duration and energy on UAS properties requires detailed investigation.
Purpose of the Study:
- To compare UAS generated by nanosecond (ns) and picosecond (ps) laser pulses.
- To investigate the effect of laser pulse energy on UAS characteristics.
- To analyze the spectral content and reflection behavior of UAS.
Main Methods:
- Experimental generation of UAS using focused 10 ns and 30 ps laser pulses.
- Time-domain analysis of UAS overpressure and arrival time.
- Time-frequency analysis using spectrograms to study spectral content and reflections.
Main Results:
- UAS overpressure decreases and arrival time increases with propagation distance for both ns and ps LIB.
- Acoustic signal overpressure scales linearly with incident laser pulse energy.
- Spectrograms reveal broad acoustic spectra (10-800 kHz) with dominant frequencies around 105 kHz and 690 kHz.
- Only the lower frequency (105 kHz) is reflected from the water-air interface; higher frequencies dissipate.
Conclusions:
- Nanosecond laser-induced breakdown is more suitable for applications requiring stronger direct and reflected acoustic signals compared to picosecond LIB.
- Pulse duration significantly impacts the spectral characteristics and reflection properties of UAS.
- Laser pulse energy is a key parameter for controlling the amplitude of generated UAS.
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