School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK.
CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, FL, 32186, USA.
Sci Rep. 2023 Jun 5;13(1):9071. doi: 10.1038/s41598-023-35990-z.
That the speed of light in vacuum is constant is a cornerstone of modern physics. However, recent experiments have shown that when the light field is confined in the transverse plane, the observed propagation speed of the light is reduced. This effect is a consequence of the transverse structure which reduces the component of wavevector of the light in the direction of propagation, thereby modifying both the phase and group velocity. Here, we consider the case of optical speckle, which has a random transverse distribution and is ubiquitous with scales ranging from the microscopic to the astronomical. We numerically investigate the plane-to-plane propagation speed of the optical speckle by using the method of angular spectrum analysis. For a general diffuser with Gaussian scattering over an angular range of 5°, we calculate the slowing of the propagation speed of the optical speckle to be on the order of 1% of the free-space speed, resulting in a significantly higher temporal delay compared to the Bessel and Laguerre-Gaussian beams considered previously. Our results have implications for studying optical speckle in both laboratory and astronomical settings.
在真空中，光速不变是现代物理学的基石。然而，最近的实验表明，当光场被限制在横截面上时，光的传播速度会降低。这种效应是由于横向结构导致光在传播方向上的波矢分量减小，从而改变了相位和群速度。在这里，我们考虑光学散斑的情况，它具有随机的横向分布，并且无处不在，其尺度从微观到天文尺度都有。我们通过使用角谱分析的方法数值研究了光学散斑的平面到平面传播速度。对于在 5°角范围内具有高斯散射的一般扩散器，我们计算出光学散斑的传播速度减缓到自由空间速度的 1%左右，与之前考虑的贝塞尔和拉盖尔-高斯光束相比，会导致显著更高的时间延迟。我们的结果对在实验室和天文环境中研究光学散斑具有重要意义。
