Few-cycle phase-stable infrared OPCPA

Few-cycle laser pulses are an important tool for investigating
laser-matter interactions. Apart from the mere resolution used in
time-resolved processes, owing to this approach table-top sources
nowadays can reach the limits of the perturbative regime and
therewith enable extreme nonlinear optics. In the visible domain,
femtosecond technology over the last decades has quickly developed,
in recent years leading to the routine generation of
carrier-envelope phase (CEP) stable few-cycle laser pulses at high
energies, using ubiquitous Ti:Sapphire amplifiers. Near to
mid-infrared few-cycle pulses in contrast can be employed for
investigating interactions in the tunneling regime. The
ponderomotive potential of the infrared light field allows quivered
charged particles to acquire large energies, leading to
applications like the generation of isolated attosecond pulses in
the water window. In this wavelength regime however, the required
sources are yet to be demonstrated or at least matured. The best
candidate for few-cycle pulses in this domain is optical parametric
amplification. This work describes the development of an optical
parametric chirped pulse amplifier (OPCPA), used to create
CEP-stable few-cycle pulses in the near infrared (NIR). It covers
all essential parts of the system. First the signal pulses are
generated from ultrashort lasers using spectral broadening
techniques in chapter 2. After compression of these white light
continua, intra-pulse broadband difference frequency generation
yields CEP stable infrared pulses spanning over more than one
octave. A thin-disk-based pump laser provides ample pump energy (20
mJ) at pulse durations around 1.5 ps. Its characterization and
optimization for OPCPA is performed in chapter 3. The high peak
energy of this pump laser leads to the buildup of optical
nonlinearities and consequently shows distinct influence on the
OPCPA system performance. The synchronization of the OPCPA pump and
seed laser system is the topic of chapter 4. This chapter is not
limited to NIR systems, but demonstrates enhanced (actively
stabilized) synchronization of the jitter between pump and seed
pulses to σ = 24 fs, which later results in improved output
stability. The NIR OPCPA centered at 2.1 μm is described in chapter
5. This combines the efforts of the previous chapters and describes
the generation and characterization of 100 μJ sub-two-cycle
CEP-stable pulses, the shortest published to date at this energy
level. As a first prototype (cutting edge) experiment, CEP
dependent sub-fs currents in a dielectric are generated in chapter
6 using the developed light source. The results compared well to
visible few-cycle laser sources and demonstrate the usability of
the OPCPA system (beyond the charac- terizations of chapter 5) for
investigating sub-cycle carrier dynamics in dielectrics. For the
same purpose, to generate the currently most broadband NIR continua
at kHz repetition rates and mJ-level pulse energies, the OPCPA
system is further boosted and efficiently broadened to three
optical octaves using a hollow core fiber setup (described in
chapter 7). The spectral phase is characterized and demonstrates
self-compression in the NIR around 1.3 μm. The process provides
CEP-stable sub-2-cycle pulses in this regime directly, the shortest
and most powerful reported to date. Furthermore, the spectral
broadening in the infrared shows enhanced low-order harmonic gen-
eration and cross-phase-modulation as the dominant mechanism.
Experimentally the limited influence on the driver bandwidth is
investigated. It is found that the processes allow using more
efficient many-cycle infrared sources to generate several-octave
spanning, compressible continua in the future. Even partial
compression of these would then provide NIR transients for
high-field experiments.