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State-of-the-art ultrashort light sources in the visible and near-infrared spectral regions provide direct access to the femtosecond realm, thereby enabling understanding and control of electronic processes within matter. On the other hand, ultra-intense light pulses lead to the emergence of relativistic electron motion and many related phenomena, such as electron & ion acceleration and high-order harmonic generation in plasmas. The generation and amplification techniques for those intense short light pulses were developed over the last 60 years. Nowadays, they are unique scientific research tools and the basis of commercial applications. The driving forces behind many of these new optical technologies are second and third order nonlinear ultrashort processes. Optical parametric chirped pulse amplification (OPCPA) is currently the most interesting of these techniques and promises in particular high single-pass gain, broad gain bandwidth, scalability, good high-dynamic range temporal contrast, and tunability. However, OPCPA comes also with a bundle of challenges. The aim of this thesis, by utilizing the advantages and facing these challenges, is to boost a sub-two cycle optical parametric synthesizer (OPS), a two-color-pumped OPCPA, to an unprecedented parameter regime in respect of energy, intensity, contrast and stability.

The presented sub-2-optical cycle OPS – the light wave synthesizer (LWS) - is a worldwide unique system, amplifying a spectral bandwidth in three pairs of OPCPA stages. One pair of these stages sequentially amplifies and coherently combines two complementary spectral ranges to an almost octave spanning bandwidth. The amplified spectrum ranges from 580 nm to 1000 nm, which makes Fourier limited pulses with 4.6 fs possible. The present system is a fundamental reconstruction and extension of a former version of LWS that provided peak powers of up to 16 TW. By carefully redesigning of the former OPCPA stages, implementing a new front end and adding two nominally 2.3 J Nd:YAG amplifiers, harmonic generation setups and a third pair of OPCPA stages, the pulse energy has been raised up to 450-500 mJ while keeping the spectral bandwidth. After compression, this corresponds to about the aspired 100 TW peak power.

Focus was also laid on various important parameters for such ultra-short and ultra-intense light pulses, such as the temporal contrast, the carrier-envelope phase (CEP) and energy stability. Analysis and optimization of the 16 TW LWS version operation parameters made it possible to optimize the LWS-100 root mean square energy stabilities down to 0.3-0.5% over 100 s, which is significantly lower than previously reported for the former version. For the first time, the CEP-stability for this full system has been demonstrated. Currently, it is limited by slow drifts, but an active feedback system could suppress this to 400 mrad. The influences on the temporal contrast were investigated and prepulses identified and eliminated. Furthermore, hardware and software control for easy handling and reliable operation have been implemented.

The LWS-100 pushes the limits for few-cycle laser technology even further. It enables the generation of intense and isolated attosecond pulses beyond 100 eV photon energy, acceleration of attosecond electron bunches to relativistic energies, measurement of nonlinear processes of inner shell electrons via XUV pump-probe experiments and generation of isolated attosecond pulses on plasma mirrors. 

Pulses of light that are both ultrashort and ultraintense are often generated using optical parametric amplifiers (OPA). These are capable of driving highly non-linear interactions with matter, which are interesting when studying the fundamental laws of our universe. Furthermore, they are also used in many scientific and industrial applications, such as particle accelerators, inertial-confinement nuclear fusion, and medical diagnostics and treatment. This thesis explores the diagnostic and optimization of pulses of light with extreme properties and utilizes them to drive electron acceleration.

The applied light pulses with very short duration (<5 fs) and high peak power (>10 TW) are sensitive to develop spatio-temporal aberrations. These are color-dependent distortions that can significantly degrade the pulse properties, like peak-intensity, and affect their applicability. Furthermore, in most cases they are not easy to correctly diagnose, with current tools failing to provide widely applicable solutions. In this thesis, we describe a new type of spatio-temporal coupling that is especially relevant for optical parametric synthesizers (OPS), systems that coherently combine multiple OPA stages. To do this, we have contributed to the development of two methods for the characterization of such aberrations, the so-called simplified-INSIGHT and HASO multispectral. These enabled us to further improve the structure of our OPS and laser systems.

We also explored the applicability of light pulses to drive relativistic electron acceleration in vacuum. To this end, an injection system using nanotips is presented, capable of inserting electrons spatially in the focus and temporally in the most intense light-cycle. This way, vacuum laser accelerated electrons of up to 14 MeV were detected using a tight focusing configuration (f#1) and their properties characterized. Furthermore, we investigated the dependence of the acceleration process when the focusing geometry is relaxed (f#3). This resulted in the unexpected outcome of similar electron energies in both cases, although the intensity was ten times reduced. This indicates that the decrease in accelerating field strength is compensated by longer acceleration lengths, which is not predicted by currently existing analytical models.