Speaker
David Turnbull
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.206.pdf
Flying Focus and its Application to Plasma-Based Laser Amplifiers
D. Turnbull1 , S.-W. Bahk1 , I. A. Begishev1 , R. Boni1 , J. Bromage1 , S. Bucht1 ,
A. Davies1 , P. Franke1 , D. Haberberger1 , J. Katz1 , T. J. Kessler1 ,
A. L. Milder1 , J. P. Palastro1 , J. L. Shaw1 , and D. H. Froula1
1 University of Rochester Laboratory for Laser Energetics, Rochester, USA
An advanced focusing scheme called a “flying focus” has been demonstrated, in which a
diffractive lens combined with a chirped laser pulse enables a small-diameter laser focus to
propagate nearly 100× its Rayleigh length [1]. Furthermore, the speed at which the focus—
and therefore the peak intensity—moves is decoupled from the group velocity of the laser; it
was demonstrated to co- or counter-propagate along the laser axis at any velocity. Experiments
validating the concept measured subluminal (−0.09c) to superluminal (39c) focal-spot veloci-
ties, generating a nearly constant peak intensity over 4.5 mm. We propose a new laser amplifier
scheme utilizing stimulated Raman scattering in plasma in conjunction with such a flying focus
[2]. Pump-intensity isosurfaces are made to propagate at v ≈ −c so as to be in sync with the
injected counter-propagating seed pulse. By setting the pump intensity in the interaction region
to be just above the ionization threshold of the background gas, an ionization wave is produced
that travels a fixed distance ahead of the seed. Simulations show that this will make it possible
to optimize the plasma temperature and mitigate many of the issues that are known to have
impacted previous Raman amplification experiments, in particular, the growth of precursors. In
addition to plasma-based laser amplifiers, the spatiotemporal control of laser intensity provided
by the flying focus could mitigate dephasing in other plasma devices that produce, for example,
tunable radiation and/or fast particles.
This material is based upon work supported by the Department of Energy National Nuclear
Security Administration under Award Number DE-NA0001944, the University of Rochester,
and the New York State Energy Research and Development Authority.
References
[1] D. H. Froula et al., “Spatiotemporal Control of Laser Intensity,” to be published in Nature Photonics.
[2] D. Turnbull et al., Phys. Rev. Lett. 120, 024801 (2018).
