Origin of Gouy Phase Shift Identified by Laser-Generated Focused Ultrasound
Origin of Gouy Phase Shift Identified by Laser-Generated Focused Ultrasound
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DOI：
10.1021/acsphotonics.0c01313
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发表时间：
2020-11-18
期刊：
影响因子：
7
通讯作者：
Guo, L. Jay
中科院分区：
文献类型：
--
作者：
Lee, Taehwa;Cheong, Yeonjoon;Guo, L. Jay
古伊相移，即通过焦点的会聚波的相变，是任何类型的波（包括光和声）的一般特征。相移的直接观察通常仅限于高频短脉冲，例如太赫兹光脉冲和皮秒声脉冲。我们展示了相对低频、兆赫兹超声的古伊相移，广泛应用于超声成像和传感。该演示通过实验实现，通过纳秒激光激发吸光凹面薄膜产生单极超声波脉冲，该凹面薄膜从聚焦前到聚焦后经历极性反转。此外，我们对各种输入压力分布的模拟结果表明，对于具有显着衍射的光束观察到古伊相移。基于惠更斯原理和二次波的声干涉，直观地解释了相位异常的物理起源，也为光学中的古伊相移提供了进一步的理解。
The Gouy phase shift, the phase change of a converging wave passing through a focus, is a general characteristic of waves of any kind, including light and sound. Direct observation of the phase shift has been typically limited to high-frequency short pulses, e.g., terahertz light pulses and picosecond sound pulses. We demonstrate the Gouy phase shift of relatively low-frequency, megahertz ultrasound, widely implemented for ultrasound imaging and sensing. This demonstration is experimentally enabled with monopolar ultrasound pulses generated by nanosecond laser excitation of a light-absorbing concave film, which undergoes polarity reversal from before to after focusing. Moreover, our simulation results for various input pressure profiles show that the Gouy phase shift is observed for beams with significant diffractions. The physical origin of the phase anomaly is intuitively explained based on Huygens' principle and the acoustic interference of secondary waves, providing further understanding of the Gouy phase shift in optics as well.