Traditionally, laser pulses have been manipulated in space or time, but recently we have started to exploit techniques that allow us to couple space and time in order to control the intensity peaks at focus. For example, using a diffractive lens to focus a chirped laser pulse allows the intensity peak to propagate at any velocity, even faster than the speed of light, while maintaining a high intensity over 100s of times the systems Rayleigh length. The ability to match the velocity trajectory of the intensity over long distances to various laser-plasma applications has opened a rich area of physics. This talk will introduce spatiotemporal pulse shaping and how it can be used to generate a flying focus—an intensity peak that can propagate at any velocity over very long distances. We have applied the flying focus to three grand challenge laser-plasma applications: laser wakefield acceleration, photon acceleration, and nonlinear Thomson scattering.
In laser-wakefield acceleration, applying spatiotemporal pulse shaping in simulations has demonstrated a new regime where the velocity of the laser’s intensity peak was matched to the electrons velocity, therefore eliminating dephasing, and allowing the system to be optimized at higher densities that traditional plasma accelerators. Applying this concept to EP OPAL, a high-power laser under development at the University of Rochester (500 J/20 fs), suggests that a single-stage plasma accelerator could accelerate electrons to 100s of GeV over a few meters without the need for optical guiding structures.
By propagating a flying focus in a gas, simulations and subsequently experiments have demonstrated the ability to create ionization waves that can propagate at arbitrary velocity. Simulations show that these ionization waves of arbitrary velocity can be used to frequency shift optical light from the visible (400 nm) to the XUV (100 nm) over a 50 microns while ultimately generating attosecond high-power pulses.
Finally, the flying focus has opened up a novel regime of nonlinear Thomson scattering by allowing the velocity of the intensity peak to be matched to the velocity of a counter propagating electron beam over long distances. This concept decouples the frequency of the radiation from the intensity of the laser pulse, increases the radiated power over conventional Compton scattering, and reduces the radiation into a beam-like cone, which decreases with increasing laser intensity. For a normalized laser intensity of 10, the brightness is increased by 108 over conventional Compton scattering.
This material is based upon work supported by the Department of Energy Office of Fusion Energy under Award Numbers DE-SC0016253, DE-SC0019135, and DE-SC0017950.
CLICK HERE to view the colloquium presentation.