Get started
Work

Ultrafast ytterbium-based laser sources and diagnostics for efficient high-order harmonic generation

Year: 2024
Type: dissertation
Abstract: High-order harmonic generation (HHG) supplies extreme ultraviolet (XUV) radiation with attosecond pulse duration for a wide variety of applications from fundamental research to industry. As HHG is a very inefficient process, enhancing the XUV flux is of great interest. Hereby, either the HHG process itself or the laser which is the primary driver of HHG can be optimized.Currently, the technology is shifting from Titanium:Sapphire (Ti:Sa) to Ytterbium-based (Yb) laser systems as the latter are able to supply much higher average powers, benefiting the XUV flux. However, Yb amplifiers deliver pulse durations much longer than those of Ti:Sa systems. A significant part of this thesis is dedicated to post-compression of pulses to shorter durations with multi-passcells (MPCs) demonstrating high efficiencies and scalability to the desired peak power regime. A compact and cost-effective experimental setup that uses thin glass plates as the nonlinear medium compresses 300 fs long pulses from an Yb amplifier with a peak power of 370 MW down to 31 fs. Output peak-powers of > 2.5 GW with a transmission of 87 % and a repetition rate of 200 kHz were achieved, demonstrating a promising perspective for MPCs as HHG drivers.To accurately judge the quality of ultrashort laser pulses a lot of emphasis was placed on pulse characterization methods, as knowing the exact generation conditions for HHG benefits the understanding of the HHG optimization possibilities immensely. This thesis includes the results from two novel methods developed within the scope of this research work: retrieval of a time-dependent polarization state with the dispersion scan method as well as single-shot carrier-envelope phase measurements via optical Fourier transform.Optimizing the yield of HHG in a specific XUV spectral range can also be done by tuning the trajectories of the electrons during the HHG process. By combining a turn-key Yb laser with its second harmonic in a waveform synthesizer built for maximum pulse parameter control, two-color HHG was investigated with the emphasis on finding the optimum laser field parameters, consisting of the relative color ratio and phase, to enhance the XUV flux for a specific harmonic order. A simple law based on electron trajectories is derived and experimentally verified, relating the laser field parameters to the yield enhancement of a single harmonic order.
Author: Raab, Ann-Kathrin
Institution: Lund University
Language: English
Open Access status: green
OpenAlex ID: W7034465797
Cites:
Cited by:
Related to: