Fundamental Limitations in the Measurement and Stabilization of the Carrier-Envelope Phase of Ultrashort Laser Pulses

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The stabilization of the carrier-envelope phase of ultrashort laser pulses
went through a rapid development from the first publication of a feasible
concept in 1999 to being a mature tool for frequency metrology and attosecond
science now. Using this technique, stabilization of the timing between the
carrier wave and the envelope of a laser pulse with residual jitters of only 100
attoseconds has become possible. Naturally, the questions arises whether and
how this can be further improved.
The current work is devoted to determining the physical mechanisms which
generate jitter in carrier-envelope phase stabilization. Furthermore, it is investigated
whether there is a fundamental limitation to the achievable accuracy.
To this end, two methods for removal of technical noise contributions are
initially discussed. Different interferometer topologies are investigated and
spurious interferometer noise is reduced by more than 40% using a commonpath
layout. A novel two-detector based carrier-envelope phase retrieval technique
for amplified laser pulses is demonstrated enabling the circumvention of
the shot-noise constraint of the conventional extraction method to the maximum
extent possible. Next, a novel feed-forward stabilization concept is
developed that enables carrier-envelope phase stabilizations with only 20 attosecond
residual timing jitter between carrier and envelope of the laser pulse.
This feed-forward method is unconditionally stable against drop-out and permits
the generation of a train of pulses with identical electric field structure
with no additional measures. As the feed-forward concept widely avoids the
technical noise sources of the conventional feedback stabilization, the resulting
noise spectra exhibit only two unavoidable residual noise mechanisms: a highfrequency
white noise floor stemming from shot noise in the carrier-envelope
phase detection and a drift-like contribution with 1/f noise characteristics.
Finally, the drift-like residual noise mechanism is found to induce phase
noise below the level expected for the conversion of pump laser shot noise into
carrier-envelope phase jitter. A feedback based squeezing, a photon-number
squeezing process and a quantum non-demolition like conversion are discussed
as possible explanations for this striking finding. It is shown that either the
feedback squeezing or the quantum non-demolition process is the probable
origin for the observed sub-shot-noise signatures of the carrier-envelope phase
jitter.