Clark TR, Milchberg HM
Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA.
Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics. 2000 Feb;61(2):1954-65. doi: 10.1103/physreve.61.1954.
The quasibound modes of an evolving plasma waveguide were investigated by using variably delayed end-injected and side-injected probe pulses. The use of these different coupling geometries allowed the probing of the waveguide's optical modes during two temporal regimes: early-time plasma channel development, characterized by leaky optical confinement, and later channel hydrodynamic expansion characterized by stronger confinement. The wave equation was solved to determine the available quasiguided optical modes and their confinement for experimentally measured electron density profiles. The guided intensity patterns and spectra measured at the waveguide exit were successfully explained in terms of these mode solutions. The spectrum of broadband end-coupled probe pulses was found to be unaffected by the guiding process, mainly because those modes which survived to the waveguide exit were well-bound, and for strongly bound fields, the transverse mode profiles are wavelength independent. By contrast, side coupling to the quasibound modes of the plasma waveguide was seen to be highly mode and frequency selective.
通过使用可变延迟的端注入和侧注入探测脉冲，研究了演化中的等离子体波导的准束缚模。使用这些不同的耦合几何结构，可以在两个时间区域探测波导的光学模式：以泄漏光学限制为特征的早期等离子体通道发展阶段，以及以更强限制为特征的后期通道流体动力学膨胀阶段。求解波动方程以确定可用的准导光学模式及其对实验测量的电子密度分布的限制。根据这些模式解成功解释了在波导出口处测量的导光强度模式和光谱。发现宽带端耦合探测脉冲的光谱不受导光过程的影响，主要是因为那些存活到波导出口的模式是强束缚的，对于强束缚场，横向模式分布与波长无关。相比之下，等离子体波导与准束缚模的侧耦合被认为具有高度的模式和频率选择性。
