A chromatic focusing system combined with chirped laser pulses was used to create a “flying focus” . This advanced focusing scheme provides unprecedented spatiotemporal control over the laser focal volume by enabling a small-diameter laser focus to propagate over 100 times its Rayleigh length. Furthermore, the flying focus decouples the speed at which the peak intensity propagates from the group velocity of the laser pulse, allowing the laser focus to co- or counter-propagate along its axis at any velocity. Experiments have demonstrated a nearly constant intensity over 4.5 mm while the velocity of the focus ranged from subluminal (0.01c) to superluminal (15c). When increasing the laser intensity above the ionization threshold of the background gas, an ionization wave was measured to track the ionization threshold intensity isosurface as it propagated and ionization waves of arbitrary velocity were demonstrated [2,3]. Subluminal and superluminal ionization fronts were produced over the entire 4.5 mm, both forward- and backward-propagating relative to the ionizing laser. All backward and all superluminal cases mitigated the issue of ionization-induced refraction, which typically challenges the formation of long, contiguous plasma channels. The properties of the flying focus provide the opportunity to overcome dephasing in laser-plasma accelerators, but theory predicts that the overall acceleration length will remain the same. Flying focus also presents a path around current fundamental limitations in laser-plasma amplifiers , photon accelerators, ion accelerators, THz generation, and high-order frequency conversion.
This material is based upon work supported by the U.S. Department of Energy/National Science Foundation under Award # DE-SC0017950, the U.S. Department of Energy Office of Fusion Energy Sciences under Award # DE-SC0016253, the Department of Energy National Nuclear Security Administration under Award # DE-NA0001944, the University of Rochester, and the New York State Energy Research and Development Authority
|Working group||Invited plenary talk|