研究目的
To study the acoustic radiation of femtosecond laser-generated plasma filaments in air, both experimentally and theoretically, and to evaluate the directivity of the filament’s acoustic radiation within and beyond the audible frequency range.
研究成果
The acoustic radiation of laser-generated plasma filaments can be modeled using principles of linear acoustic sources. The directivity characteristics between the measurements and the model demonstrate that LIB acoustic sources can be effectively modeled and characterized via acoustic models only requiring knowledge of the dimensions of the plasma region and the axial distribution of the intensity of the plasma luminescence after plasma relaxation.
研究不足
The sound card’s bandwidth restricts the acquisition and analysis of the filament source for the complete frequency range; however, it is sufficient for analyzing the audio and near ultrasound ranges.
1：Experimental Design and Method Selection:
The study involved systematic measurements of the filament’s acoustic radiation at different directions using a Ti:Sapphire laser to generate plasma filaments. A theoretical model based on the experimental results was developed to evaluate the directivity of the filament’s acoustic radiation.
2：Sample Selection and Data Sources:
The plasma filament was generated by focusing femtosecond laser pulses in air. The luminescence of the plasma channel was captured to extract the initial pressure profile.
3：List of Experimental Equipment and Materials:
Ti:Sapphire laser (Amplitude Technologies), GRAS 46BF-1/4 in. microphone, GRAS 12AA power module, RME Fireface 802 sound card.
4：Experimental Procedures and Operational Workflow:
Acoustic signals were recorded at different positions around the source at a step of 15°, keeping a constant distance of 30 cm from the center of the plasma. The measurements were processed to extract the directivity characteristics.
5：Data Analysis Methods:
The directivity of the source was evaluated in terms of the normalized equivalent SPL Leq, calculated in ANSI S1.11-2004 octave bands.
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