Bubbles generated by acoustic cavitation may be efficient in light production by direct emission (sonoluminescence) or indirect emission (sonochemiluminescence) depending on operating parameters such as acoustic pressure and surface tension. These conditions are quite difficult to reach at very high frequencies, even by concentrating the acoustic power at a given location via focusing the acoustic field thanks to the transducer shape (High Intensity Focused Ultrasound). The current work aims at probing the cavitation bubble behaviour under short frequency sweeps by monitoring sonochemiluminescence and sonoluminescence activities. When the frequency was swept in reverse (negative sweep), an enhancement in the SCL, relative to the SCL observed under a single frequency irradiation, was observed. Conversely, a positive frequency sweep resulted in the quenching of SCL intensity. The degree of SCL enhancement and quenching was also dependent on the rate at which the frequency was being swept and on the change in the size of cavitation bubbles. The size of cavitation bubbles varied with varying starting sweep frequency (3.4, 3.6 and 4.2 MHz), affecting both SCL and sonoluminescence (SL) emissions. The addition of a surfactant (sodium dodecyl sulphate) affected the observed results, possibly due to its influence on coalescence between cavitation bubbles. The results suggest that the enhancement and quenching are related to the response of bubbles generated by the starting frequency to the direction of the frequency sweep and the influence of the sweep rate on growth and coalescence of bubbles, which affected the population of the active bubbles.

中文翻译：

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扫频对超声发光和声致发光的影响。

根据操作参数（例如声压和表面张力）的不同，通过声空化产生的气泡在通过直接发射（共振发光）或间接发射（共振发光）产生的光中可能是有效的。由于换能器的形状（高强度聚焦超声），即使通过聚焦声场将声功率集中在给定位置，也很难在很高的频率下达到这些条件。当前的工作旨在通过监测超声发光和声致发光活动来探测短频扫描下的空化气泡行为。当反向扫描频率（负扫描）时，相对于在单频照射下观察到的SCL，观察到SCL增强。反过来，正频率扫描导致SCL强度淬灭。SCL增强和淬灭的程度还取决于扫频的速率和空化气泡大小的变化。空化气泡的大小随起始扫描频率（3.4、3.6和4.2 MHz）的变化而变化，从而影响SCL和声致发光（SL）发射。添加表面活性剂（十二烷基硫酸钠）影响观察到的结果，可能是由于其对空化气泡之间的聚结的影响。结果表明，增强和猝灭与由起始频率产生的气泡对扫频方向的响应以及扫频速率对气泡的生长和聚结的影响有关，后者影响了活性气泡的数量。