Researchers have combined a fiber-laser system with recent advancements in
multi-pass cells to create a laser with a unique combination of few-cycle
pulses at high average power, pulse energy and repetition rate and with
stable carrier envelope phase (CEP) operation. These characteristics make
the new laser ideal for driving next generation attosecond sources, such as
those at the Extreme Light Infrastructure (ELI) in Europe.
ELI, the world's largest and most advanced high-power laser infrastructure,
will be used to investigate light-matter interactions at the highest
intensities and shortest time scales. The beam lines of ELI's Attosecond
Light Pulse Source will provide unprecedented performance in generating
isolated attosecond pulses and thus have very demanding laser system
requirements.
Steffen Hädrich from Active Fiber Systems GmbH in Germany will present the
new laser at the Optica (formerly OSA) Laser Congress virtual web conference
3–7 October 2021. Hädrich's talk is scheduled for Monday, 4 October at 11:30
EDT (UTC 04:00).
"The development of such a unique laser system opens up new prospects for
secondary sources, e.g. for the generation of isolated attosecond pulses
with unprecedented parameters," said Hädrich. These in turn hold promise to
advance the understanding of electronic processes on fundamental length- and
time-scales and contribute to new discoveries in biology, chemistry, physics
and medicine."
To create a laser system that can meet the needs of ELI and other scientific
applications, the researchers developed a fiber-chirped pulse amplification
system that coherently combines eight amplifier channels. This system emits
300-fs pulses that are then compressed down to the few-cycle regime using
two multi-pass cells. The first multi-pass cell uses standard dielectric
mirrors to achieve 1.7 mJ pulses with a duration less than 35 fs. The second
cell uses metal-based mirrors to achieve a pulse duration of just 5.8 fs at
a pulse energy of 1.1 mJ, 110 W average power and repetition rate of 100
kHz.
Stable CEP operation is needed to fully utilize the high average power and
fast repetition rate of the laser. The researchers accomplished this by
measuring the CEP of each pulse using a single stereo-ATI phasemeter that
can characterize noise over the full frequency spectrum. The CEP
measurements were sent to a PID controller, creating a feedback loop that
enabled ~400 mrad of CEP noise.
"We demonstrated the shortest pulses and highest compressed average power
that has been achieved for few-cycle MPCs with 110 W at the 100 kHz pulse
repetition rate," said Hädrich. "With further improvements, we hope to also
achieve less than 300 mrad of CEP noise soon."
Hädrich adds, "The presented laser system meets the requirement for the HR1
laser of ELI-ALPS. We are in the process of scaling this approach towards
the HR2 parameters, i.e. to implement this concept for the demonstration of
a 500W, 5mJ, 6fs CEP-stable laser system."
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Physics