University of Rochester Laboratory for Laser Energetics, 250 E River Rd., Rochester, New York 14623, USA.
University of Rochester Department of Physics & Astronomy, B&L Hall, Rochester, New York 14627, USA.
Phys Rev Lett. 2018 Jun 1;120(22):225001. doi: 10.1103/PhysRevLett.120.225001.
Flying focus is a technique that uses a chirped laser beam focused by a highly chromatic lens to produce an extended focal region within which the peak laser intensity can propagate at any velocity. When that intensity is high enough to ionize a background gas, an ionization wave will track the intensity isosurface corresponding to the ionization threshold. We report on the demonstration of such ionization waves of arbitrary velocity. Subluminal and superluminal ionization fronts were produced that propagated both forward and backward relative to the ionizing laser. All backward and all superluminal cases mitigated the issue of ionization-induced refraction that typically inhibits the formation of long, contiguous plasma channels.
飞焦点技术使用啁啾激光束通过高色差透镜聚焦，在扩展的焦区内，峰值激光强度可以以任意速度传播。当强度足以使背景气体电离时，电离波将跟踪对应于电离阈值的强度等位面。我们报告了这种任意速度的电离波的演示。产生了亚光速和超光速的电离前沿，相对于电离激光向前和向后传播。所有向后传播和所有超光速的情况都减轻了电离诱导折射的问题，该问题通常会抑制长的连续等离子体通道的形成。
