Transversale Moden in optischen Resonatoren für Anwendungen hoher Laserintensität
Aachen / Apprimus (2017, 2018) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (ii, 234 Seiten) : Illustrationen, Diagramme
In this thesis it is shown, how an understanding of transverse modes in optical resonators, in particular in an enhancement resonator and in a periodic arrangement or multi-pass cell, allows finding and implementing new approaches to overcome limitations. In the case of the enhancement resonator it is shown, how the combination of simultaneously resonant transverse modes in a quasi-imaging resonator can be used to achieve a geometrical output coupling of harmonics generated inside the resonator. With the simple slit mode composed of the Gauss-Hermite modes GH[0,0] and GH[4,0] an enhancement of the circulating power compared to the impinging power of 330 is demonstrated. With the same transverse mode, an enhancement of 50 and circulating power of 2.2 kW, harmonics have been generated inside the resonator. The power coupled out through a slit mirror reaches 11 μW for the 17th harmonic with 61 nm wavelength, which corresponds to a conversion efficiency of 2.4E-7 referred to the impinging power of 45 W. The output coupling efficiency of the harmonics from the resonator is estimated to 30%, which is larger than the efficiencies for established methods (plate at Brewster’s angle, XUV grating). This shows how together with an improved spatial overlap by mode-matching of the impinging beam to the circulating slit mode and with an increased impinging power, output-coupled XUV powers in the mW range come into reach. Within this thesis a new scheme for nonlinear pulse compression has been developed, making a parameter range accessible, which could not be reached with established schemes relying on spectral broadening in a waveguide. The spectral broadening via self-phase modulation in a multi-pass cell (MPCSB) allows compression of pulses with a peak power larger than the critical power for self-focusing of the nonlinear medium. In contrast to spectral broadening at a single pass through a nonlinear medium, a homogeneous spectral broadening across the beam profile as well as a large efficiency is achieved. The scheme is suitable for high average powers, non-diffraction-limited beam quality and is insensitive against fluctuations of the beam axis. The multi-pass cell is designed such that the influence of the Kerr lens which inevitably goes along with self-phase modulation onto the transverse mode of the beam is small and a resonant coupling to higher transverse modes is avoided. Nonlinear pulse compression from 850 fs to 170 fs with a compressed pulse energy of 37.5 μJ and average power of 375 W at 10 MHz repetition rate as well as compression from 860 fs to 115 fs with 7.5 μJ pulse energy and 300 W average power at 40 MHz repetition rate are demonstrated. In both cases the compression efficiency is >90% and the beam quality close to the diffraction limit is preserved. These pulse parameters achieved for the first time allow amongst others the scaling of the driving power at resonator-assisted high-harmonic generation. Together with the geometrical output coupling, they therefore represent an important step towards the realization of an XUV frequency comb, which will allow high-precision spectroscopy of the 1s-2s transition in He+ and a test of quantum electrodynamics.