The photoacoustic effect was employed to generate short-duration quasi-unipolar acoustic pressure pulses in both planar and spherically focused geometries. In the focal region, the temporal profile of a pressure pulse can be approximated by the first derivative of the temporal profile near the front transducer surface, with a time-averaged value equal to zero. This approximation agreed with experimental results acquired from photoacoustic transducers with both rigid and free boundaries. For a free boundary, the acoustic pressure in the focal region is equal to the sum of a positive pressure that follows the spatial profile of the optical energy deposition in the medium and a negative pressure that follows the temporal profile of the laser pulse.

中文翻译：

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聚焦准单极压力脉冲的光声产生

光声效应用于在平面和球形聚焦几何形状中产生短时准单极声压脉冲。在焦点区域，压力脉冲的时间分布可以通过前换能器表面附近的时间分布的一阶导数来近似，时间平均值为零。这种近似与从具有刚性和自由边界的光声换能器获得的实验结果一致。对于自由边界，焦点区域的声压等于介质中光能沉积空间分布的正压和激光脉冲时间分布的负压之和。