Kovsh D, Hagan D, Van Stryland E
Opt Express. 1999 Apr 12;4(8):315-27. doi: 10.1364/oe.4.000315.
We present the results of modeling of nanosecond pulse propagation in optically absorbing liquid media. Acoustic and electromagnetic wave equations must be solved simultaneously to model refractive index changes due to thermal expansion and/or electrostriction, which are highly transient phenomena on a nanosecond time scale. Although we consider situations with cylindrical symmetry and where the paraxial approximation is valid, this is still a computation-intensive problem, as beam propagation through optically thick media must be modeled. We compare the full solution of the acoustic wave equation with the approximation of instantaneous expansion (steady-state solution) and hence determine the regimes of validity of this approximation. We also find that the refractive index change obtained from the photo-acoustic equation overshoots its steady-state value once the ratio between the pulsewidth and the acoustic transit time exceeds a factor of unity.
我们展示了纳秒脉冲在光吸收液体介质中传播的建模结果。必须同时求解声波和电磁波方程，以模拟由于热膨胀和/或电致伸缩引起的折射率变化，这些在纳秒时间尺度上是高度瞬态的现象。尽管我们考虑的是具有圆柱对称性且傍轴近似有效的情况，但这仍然是一个计算密集型问题，因为必须对光束在光学厚介质中的传播进行建模。我们将声波方程的完整解与瞬时膨胀近似（稳态解）进行比较，从而确定该近似的有效性范围。我们还发现，一旦脉冲宽度与声传播时间的比值超过1，从光声方程获得的折射率变化会超过其稳态值。
