High-power mid-infrared femtosecond laser pulses

The rising interest in laser sources at uncommon wavelength with a huge variety of system parameters poses a high demand on the adaptability of laser sources to a specific application. A source whose properties can be adjusted without changing its underlying concept is especially valuable for research laser labs, where demands on the sources are changing rapidly. A concept that is customisable in many ways is optical parametric chirped pulse amplification (OPCPA). It can amplify laser pulses of very low energy at wavelength ranging from UV to deep IR, because it is not relying on suitable optical transitions in the laser material like in classical laser amplifiers. Furthermore during amplification no energy is deposited in the material, facilitating power as well as repetition rate and energy scaling. Nevertheless, to be able to use the OPCPA concept for few-cycle pulse amplification, a combination of pump and output wavelengths needs to be found, enabling broadband amplification in the used optical parametric amplification (OPA) crystal. The use of a high-power pump laser usually restricts the pump wavelength to the spectral region close to 1 µm. Unfortunately this wavelength does not favour broadband amplification of many spectral regions. One solution to overcome this limitation is the use of quasi-phasematching (QPM) technology to enable efficient energy transfer from the pump to all wavelengths of the seed pulses. It can be used to amplify laser pulses at wavelengths throughout the whole transparency range of the used amplification crystal. By imprinting a suitable QPM grating structure into the crystal, one can select a spectral window to be amplified. Implementing sophisticated QPM gratings, it is even possible to engineer the output properties of the amplified pulses, for example the temporal shape or the optical spectrum. Within the scope of this thesis the successful integration of chirped QPM gratings for the amplification of few-cycle laser pulses is demonstrated. This yields a highly flexible source for generating ultra short laser pulses.