Ionization Waves of Arbitrary Velocity*

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 [1]. When that intensity is high enough to ionize a background gas, an ionization wave will track the intensity isosurface corresponding to the ionization threshold [2]. We report on the demonstration of such ionization waves of arbitrary velocity (IWAV’s) [3]. 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. IWAV’s can be used to optimize plasma-based laser amplifiers [4], photon accelerators, and many other applications.

[1] D.H. Froula et al., Nat. Photonics 12, 262 (2018).

[2] J. P. Palastro et al., Phys. Rev. A 97, 033835 (2018).

[3] D. Turnbull et al., Phys. Rev. Lett. 120, 225001 (2018).

[4] D. Turnbull et al., Phys. Rev. Lett. 120, 024801 (2018).