Generation, characterization and application of infrared few-cycle light pulses

Sammanfattning: In recent decades, laser systems emitting pulses of light containing only a few electric field oscillations under their envelope have become common in many ultrafast optics laboratories. Owing to unique temporal characteristics and achieving extreme field strengths, these so-­called few­-cycle pulses have been instrumental in unlocking new regimes of light-­matter interaction.The work presented in this thesis is focused on mastering the techniques to generate and characterize few­-optical-­cycle light pulses in the near­ and short-wave infrared spectral regions. Two systems based on optical parametric chirped pulse amplification (OPCPA) are presented. Derived from the same laser front-end, they both deliver sub­-2.5-­cycle pulses at high repetition rate (200 kHz) with a stable electric field waveform. The first laser source is a near-­infrared OPCPA delivering 6 fs pulses at a carrier of 850 nm which was upgraded during this thesis. The upgrade resulted in a boost of the output pulse energy from 8 μJ to 15 μJ without loss in pulse quality. The second laser source is a few­cycle OPCPA around 2 μm, emitting <16 fs pulses with 13 μJ of pulse energy, which was developed entirely during the thesis. We tested the capabilities of this system by driving high-­order harmonic generation (HHG) in argon gas.As a promising alternative route for few­-cycle pulses, nonlinear pulse post­compression based on multipass cells (MPCs) was investigated. It is an efficient way of reducing the pulse duration of high­-power Ytterbium (Yb) lasers. In this thesis, two MPC­-based compression experiments are presented. Firstly, 1.2 ps pulses from a mJ­-level Yb amplifier were compressed to 13 fs with two consecutive gas­-flled MPCs. Secondly, the output of another Yb amplifier was compressed from 300 to 31 fs using a bulk MPC while preserving high beam quality.Successful development of such systems is impossible without careful characterization of the output pulses. Throughout the thesis, we relied on the extensive use of the dispersion scan (d­-scan) pulse characterization technique. We demonstrate the powerful capabilities and versatility of the second­harmonic d­-scan by measuring pulses of different durations and central wavelengths in scanning and single­-shot configurations.Lastly, the few-­cycle light pulses were applied to two-­color photoionization experiments and the study of lightwave-­driven currents in semiconductors at high repetition rates.