High-power high-repetition-rate 1-$\mu$M fiber laser system for strong-field physics and mid-infrared generation

Because of their ultrashort pulse duration and extremely high peak power, interest in ultrashort pulse lasers for strong-field experiments has been rapidly increasing over the past decades. After the invention of passively mode-locked lasers, further developments of ultrashort pulses in achieving ultrashort pulse duration, extremely high peak power and phase stabilization enable scientists to do frontier research such as bio-imaging, astronomical spectroscopy, solid-state high-harmonic generation, optical-field-driven electron emission from nanostructures, light-matter interaction in new materials, etc. A breakthrough in pulse amplification of ultrashort laser pulses, including fiber lasers, to extremely high levels was accomplished through chirped-pulse amplification. High power fiber lasers realized by using large-mode-area photonic crystal gain fibers become popular in strong-field applications due their compactness, stability and perfect beam profile. Furthermore, high power fiber lasers can also serve as front-end lasers for subsequent solid-state laser amplifiers and nonlinear frequency conversion stages to enable applications such as high power mid-infrared generation, terahertz-driven linear electron acceleration, etc. High repetition rates are also a very important characteristic of ultrashort pulse lasers besides the pulse duration and the pulse peak power. This can extremely improve the photon flux and signal-to-noise ratio in many state-of-the-art strong-field experiments. However, especially in parametric amplifiers, realizing high repetition rate ultrafast lasers with high average power is still limited by the crystal size and remaining thermal effects. The aim of this thesis is to develop and provide a roadmap to build well dispersion managed, high power, repetition rate tunable 1-µm all-fiber lasers and mid-infrared lasers based on nonlinear frequency conversion. Such lasers are heavily needed in strong-field applications. Here, we demonstrate a MHz-level fiber laser system with >55 µJ pulse energy using chirped-pulse amplification. The repetition rate system can be further tuned, here reduced, by applying an acousto-optic modulator. Amplified pulses at ≈ns pulse duration can be compressed to near transform-limited duration with a grating pair compressor due to a well-engineered dispersion management. The method of hundred-watts-level circularly polarized pre-chirp managed amplification is invented and proven for the first time in this thesis. This method indicates that the peak power of the circularly polarized pulse can be amplified to 1.5 times higher than the linearly polarized pulse accumulating the same nonlinear phase. We also applied the method of optical parametric amplification to generate high repetition rate mid-infrared lasers using the high repetition rate, high power, 1-µm lasers. µJ-level, few-cycle, passively CEP-stable, 2.1-µm pulses at MHz-level repetition rate have been generated in dispersion-managed OPAs. The broadband 2.1-µm seed is generated from the chirped-pulse DFG stage. Ideas for further experiments to generate high repetition rate mid-infrared sources with much longer wavelength are also presented in this thesis. Our work paves the way to construct high repetition rate ultrafast sources satisfying the needs of many applications requiring high optical intensities, high photon flux and high signal-to-noise ratio