  Large scale laser facilities are needed to advance the energy frontier in
high energy physics and accelerator physics. Laser plasma accelerators are core
to advanced accelerator concepts aimed at reaching TeV electron electron
colliders. In these facilities, intense laser pulses drive plasmas and are used
to accelerate electrons to high energies in remarkably short distances. A laser
plasma accelerator could in principle reach high energies with an accelerating
length that is 1000 times shorter than in conventional RF based accelerators.
Notionally, laser driven particle beam energies could scale beyond state of the
art conventional accelerators. LPAs have produced multi GeV electron beams in
about 20 cm with relative energy spread of about 2 percent, supported by highly
developed laser technology. This validates key elements of the US DOE strategy
for such accelerators to enable future colliders but extending best results to
date to a TeV collider will require lasers with higher average power. While the
per pulse energies envisioned for laser driven colliders are achievable with
current lasers, low laser repetition rates limit potential collider luminosity.
Applications will require rates of kHz to tens of kHz at Joules of energy and
high efficiency, and a collider would require about 100 such stages, a leap
from current Hz class LPAs. This represents a challenging 1000 fold increase in
laser repetition rates beyond current state of the art. This whitepaper
describes current research and outlook for candidate laser systems as well as
the accompanying broadband and high damage threshold optics needed for driving
future advanced accelerators.
