This thesis covers the few-cycle laser-driven acceleration of
electrons in a laser-generated plasma. The so-called \emph{laser
wakefield acceleration} is a long-known concept that relies on
strongly driven plasma waves for the generation of accelerating
gradients in the range of several 100 GV/m. This value is
approximately four orders of magnitude larger than the one
attainably by classic accelerators, which is limited essentially
by electrical breakdown in the accelerating structures to
approximately 100 MV/m. Since the acceleration length necessary
for obtaining a certain electron energy is inversely proportional
to the accelerating field, this leads also to a drastic reduction
of the size and of the price of the accelerator. Furthermore, the
special properties of laser accelerated electron pulses, namely
the ultrashort pulse duration, the high brilliance, and the high
charge density, open up new possibilities in many applications of
these electron beams.
The laser system employed in this work is a new development based
on optical parametric chirped pulse amplification and is the only
multi-TW few-cycle laser in the world. It allows for the
amplification of pulses with a duration of 8 fs up to a power of
6.5 TW. In the experiment, the laser beam is focused onto a
supersonic helium gas jet which leads to the formation of a plasma
channel. The laser pulse, having an intensity of 10^19
W/cm^2 propagates through the plasma with an electron density of
2x10^19 cm^(-3) and forms via a highly nonlinear
interaction a strongly anharmonic plasma wave. The amplitude of
the wave is so large that the wave breaks, thereby injecting
electrons from the background plasma into the accelerating phase.
The energy transfer from the laser pulse to the plasma is so
strong that the maximum propagation distance is limited to the 0.1 mm
range. Therefore, gas jets specifically tuned to these
requirements have to be employed. The properties of microscopic
supersonic gas jets are thoroughly analyzed in this work. Based on
numeric flow simulation, this study encompasses several extensive
parameter studies that illuminate all relevant features of
supersonic flows in microscopic gas nozzles. This allowed the
optimized design of de Laval nozzles with exit diameters ranging
from 0.15 to 3 mm. The employment of these nozzles in the
experiment greatly improved the electron beam quality.
After these optimizations, the laser-driven electron accelerator
now yields monoenergetic electron pulses with energies up to 50
MeV and charges between one and ten pC. The electron beam has a
typical divergence of 5 mrad and comprises an energy spectrum that
is virtually free from low energetic background. The electron
pulse duration could not yet be determined experimentally but
simulations point towards values in the range of 1 fs. The
acceleration gradient is estimated from simulation and experiment
to be approximately 0.5 TV/m. The electron accelerator is
routinely operated at 10 Hz, which is a unique feature among laser
based accelerators. The light amplification technique employed in
the laser system in principle allows here improvements by several
orders of magnitude