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High-Order Harmonics- Characterisation, Optimisation and Applications

Lyngå, Claire LU (1999) In Lund Reports in Atomic Physics LRAP-248.
Abstract
Recent advances in laser technology, with the development of extremely short-pulse, high-intensity lasers, have opened doors to new areas in atomic physics. By focusing light from an intense, short-pulse laser into a gas jet, the emission of high-order harmonics of the laser frequency has been studied. The aim of this work has been two-fold: to better understand the underlying physics of the harmonic generation process and to demonstrate the use of the generated radiation in novel applications.



Experiments have been performed using both femtosecond and picosecond laser systems. The temporal coherence of harmonic radiation has been measured and characterised. We have shown that the far-field pattern of high-order... (More)
Recent advances in laser technology, with the development of extremely short-pulse, high-intensity lasers, have opened doors to new areas in atomic physics. By focusing light from an intense, short-pulse laser into a gas jet, the emission of high-order harmonics of the laser frequency has been studied. The aim of this work has been two-fold: to better understand the underlying physics of the harmonic generation process and to demonstrate the use of the generated radiation in novel applications.



Experiments have been performed using both femtosecond and picosecond laser systems. The temporal coherence of harmonic radiation has been measured and characterised. We have shown that the far-field pattern of high-order harmonics separates into two spatial regions with different coherence properties. These features have been related mainly to the single-atom response, but also influenced by different phase-matching conditions. For the central region we find long coherence times, close to the expected duration of the harmonic pulse.



The harmonic spectra from molecular gases have been investigated. They were found to be very similar to those obtained in rare gases, with a plateau and a cutoff whose location is strongly correlated to the ionisation potential. The conversion efficiency in the investigated molecules was not higher than that in one of the rare gases suitable for the specific wavelength region.



Applications using harmonic radiation as a narrowband, coherent XUV source have been performed. Spectroscopic measurements have been made using harmonic radiation produced from a tunable laser source. Lifetimes of highly excited states in CO have been determined and the energy dependence of the photo-ionisation cross-sections of highly excited states in He has been measured. XUV interferometry using harmonic radiation has been demonstrated with femtosecond resolution, using the 11th harmonic of a femtosecond laser, to probe the spatial variation of the electron density in a plasma. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Pierre Agostini, Pierre Agostini
organization
publishing date
type
Thesis
publication status
published
subject
keywords
high-harmonic generation, VUV spectroscopy, high-power lasers, Atomic and molecular physics, radiative lifetimes, XUV spectroscopy, Atom- och molekylärfysik, Fysicumarkivet A:1999:Lyngå
in
Lund Reports in Atomic Physics
volume
LRAP-248
pages
171 pages
publisher
Department of Physics, Lund University
defense location
Lecture Hall B, Physics Department
defense date
1999-11-19 10:15
external identifiers
  • Other:ISRN: LUTFD2/(TFAF-1040)/1-75/(1999)
ISBN
91-628-3840-7
language
English
LU publication?
yes
id
5efbe789-65e8-4d2c-a4d7-e7640d0cbcd9 (old id 40002)
date added to LUP
2007-08-01 14:09:31
date last changed
2016-09-19 08:45:11
@phdthesis{5efbe789-65e8-4d2c-a4d7-e7640d0cbcd9,
  abstract     = {Recent advances in laser technology, with the development of extremely short-pulse, high-intensity lasers, have opened doors to new areas in atomic physics. By focusing light from an intense, short-pulse laser into a gas jet, the emission of high-order harmonics of the laser frequency has been studied. The aim of this work has been two-fold: to better understand the underlying physics of the harmonic generation process and to demonstrate the use of the generated radiation in novel applications.<br/><br>
<br/><br>
Experiments have been performed using both femtosecond and picosecond laser systems. The temporal coherence of harmonic radiation has been measured and characterised. We have shown that the far-field pattern of high-order harmonics separates into two spatial regions with different coherence properties. These features have been related mainly to the single-atom response, but also influenced by different phase-matching conditions. For the central region we find long coherence times, close to the expected duration of the harmonic pulse.<br/><br>
<br/><br>
The harmonic spectra from molecular gases have been investigated. They were found to be very similar to those obtained in rare gases, with a plateau and a cutoff whose location is strongly correlated to the ionisation potential. The conversion efficiency in the investigated molecules was not higher than that in one of the rare gases suitable for the specific wavelength region.<br/><br>
<br/><br>
Applications using harmonic radiation as a narrowband, coherent XUV source have been performed. Spectroscopic measurements have been made using harmonic radiation produced from a tunable laser source. Lifetimes of highly excited states in CO have been determined and the energy dependence of the photo-ionisation cross-sections of highly excited states in He has been measured. XUV interferometry using harmonic radiation has been demonstrated with femtosecond resolution, using the 11th harmonic of a femtosecond laser, to probe the spatial variation of the electron density in a plasma.},
  author       = {Lyngå, Claire},
  isbn         = {91-628-3840-7},
  keyword      = {high-harmonic generation,VUV spectroscopy,high-power lasers,Atomic and molecular physics,radiative lifetimes,XUV spectroscopy,Atom- och molekylärfysik,Fysicumarkivet A:1999:Lyngå},
  language     = {eng},
  pages        = {171},
  publisher    = {Department of Physics, Lund University},
  school       = {Lund University},
  series       = {Lund Reports in Atomic Physics},
  title        = {High-Order Harmonics- Characterisation, Optimisation and Applications},
  volume       = {LRAP-248},
  year         = {1999},
}