Other Contributors: Massachusetts Institute of Technology. Department of Electrical Engineering and Information Technology.
Consultant: Franz X. Krtner.
Department: Massachusetts Institute of Technology. Department of Electrical Engineering and Information Technology.
Writer: Massachusetts Institute of Technology
Date Issued: 2013
High Harmonic Generation (HHG) is really a fascinating phenomenon from both fundamental and technological perspective. It enables the generation of attosecond pulses and may have applications in EUV lithography and bio-microscopy. HHG could be explained the 3 Step Model (TSM), because of the three stages from the process: ion technology, propagation and recombination. However, HHG is affected with low efficiencies along with a study, which shows the efficiency scaling with laser and material parameters is important. For any lengthy time experimentalists were only using 800 nm driver pulses from Ti:azure lasers. Using the creation of new light sources like optical parametric amplifiers, different driving wavelengths grew to become available and therefore the scaling from the single atom response versus drive wave length has attracted lots of attention. An in depth analysis implies that the efficiency scales with w50 in the cutoff and w60 in the plateau region for any fixed EUV frequency, where w0 may be the carrier frequency from the driver pulse. To know the constraints of these a source of light, we’ve created a semi-analytic model for that computation from the conversion efficiency right into a single harmonic for that plateau and cutoff regions. This model is a-dimensional, uses the TSM for that calculation from the single atom response and takes laser, material parameters and macroscopic effects into consideration.
Closed form expressions for that plateau and cutoff regions are derived and accustomed to calculate efficiencies for 400 and 800 nm driver pulses. The outcomes are in contrast to experimental ones showing excellent agreement. To be able to investigate lengthy-wave length driven HHG efficiency, the fir-D model is extended to 3 dimensions considering spatiotemporal propagation effects, for example plasma defocusing and losses because of electron-neutral inverse bremsstrahlung. These phenomena alter the phase matching along propagation, leading to non-coherent harmonic generation and therefore poor efficiencies. We further study methods to mitigate the result of plasma defocusing like using Supergaussian pulses and using Gaussian pulses with bigger beam waists. The job presented might help us develop tools to have an optimization study of HHG efficiency, to make helpful EUV sources.
Thesis (Ph. D.)–Massachusetts Institute of Technology, Department of Electrical Engineering and Information Technology, 2013.Cataloged from PDF form of thesis.Includes bibliographical references (pages 157-164).
Keywords: Electrical Engineering and Information Technology.