Few-cycle phase-stable infrared OPCPA
b'Few-cycle laser pulses are an important tool for investigating laser-matter interactions. Apart\\nfrom the mere resolution used in time-resolved processes, owing to this approach table-top\\nsources nowadays can reach the limits of the perturbative regime and therewith enable extreme\\nnonlinear 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.\\nNear to mid-infrared few-cycle pulses in contrast can be employed for investigating interactions\\nin 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.\\nThis work describes the development of an optical parametric chirped pulse amplifier (OPCPA),\\nused 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\\npulses spanning over more than one octave.\\nA thin-disk-based pump laser provides ample pump energy (20 mJ) at pulse durations around\\n1.5 ps. Its characterization and optimization for OPCPA is performed in chapter 3. The high\\npeak energy of this pump laser leads to the buildup of optical nonlinearities and consequently\\nshows distinct influence on the OPCPA system performance.\\nThe synchronization of the OPCPA pump and seed laser system is the topic of chapter 4. This\\nchapter is not limited to NIR systems, but demonstrates enhanced (actively stabilized) synchronization of the jitter between pump and seed pulses to \\u03c3 = 24 fs, which later results in improved output stability.\\nThe NIR OPCPA centered at 2.1 \\u03bcm is described in chapter 5. This combines the efforts of\\nthe previous chapters and describes the generation and characterization of 100 \\u03bcJ sub-two-cycle CEP-stable pulses, the shortest published to date at this energy level.\\nAs a first prototype (cutting edge) experiment, CEP dependent sub-fs currents in a dielectric are\\ngenerated in chapter 6 using the developed light source. The results compared well to visible\\nfew-cycle laser sources and demonstrate the usability of the OPCPA system (beyond the charac-\\nterizations of chapter 5) for investigating sub-cycle carrier dynamics in dielectrics.\\nFor the same purpose, to generate the currently most broadband NIR continua at kHz repetition\\nrates 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 \\u03bcm. The process provides CEP-stable sub-2-cycle pulses in this regime directly, the shortest and most powerful reported to date.\\nFurthermore, the spectral broadening in the infrared shows enhanced low-order harmonic gen-\\neration and cross-phase-modulation as the dominant mechanism. Experimentally the limited\\ninfluence 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.'