Optimisation and Application of Intense HighOrder Harmonic Pulses
(2001) Abstract
 The highorder harmonics that are created in the interaction between an intense laser pulse (around 10<sup>14</sup> W/cm<sup>2</sup>) and a gas medium are studied. The highorder harmonic radiation is a relatively new source of coherent radiation in the short wavelength range. The highorder harmonics are interesting for applications because of their good spatial and temporal coherence, their short pulse duration and the possibility to focus the harmonic radiation to high intensity.
The first part of this thesis focuses on optimising the highorder harmonic pulse energy. This is motivated by the relatively low conversion efficiency of highorder harmonic generation. These studies are aimed to... (More)  The highorder harmonics that are created in the interaction between an intense laser pulse (around 10<sup>14</sup> W/cm<sup>2</sup>) and a gas medium are studied. The highorder harmonic radiation is a relatively new source of coherent radiation in the short wavelength range. The highorder harmonics are interesting for applications because of their good spatial and temporal coherence, their short pulse duration and the possibility to focus the harmonic radiation to high intensity.
The first part of this thesis focuses on optimising the highorder harmonic pulse energy. This is motivated by the relatively low conversion efficiency of highorder harmonic generation. These studies are aimed to understand how the conversion efficiency can be improved. The harmonic yield as a function of medium length is studied and the different effects that influence the harmonic yield are discussed. A new geometrical configuration with two collinear foci along the propagation axis is found to improve the harmonic conversion efficiency compared to an ordinary onefocus beam. In addition, theoretical optimisations of the harmonic pulse energy are carried out. With a genetic optimisation algorithm, two or three parameters related to the characteristics of the laser beam and the nonlinear medium are varied simultaneously. Over 10<sup>9</sup> photons per pulse at a wavelength of 28 nm can be obtained.
The underlying idea of the second part of this thesis is that the highorder harmonics are potentially suitable for generating pulses of shorter duration than what is possible with current technology. With the genetic algorithm, the temporal properties of the harmonic pulse are optimised theoretically. Harmonic pulse durations as short as 6 fs are obtained, generated by a 50 fs laser pulse. The temporal coherence is optimised by selecting the transformlimited part of the harmonic spectrum. In this condition, the time profile of the harmonic radiation is a train of 265 attosecond long pulses. By experimentally manipulating the ellipticity of the laser pulse in time, one or two temporal gates of a few femtosecond duration can be created where the polarisation is linear and harmonic emission is efficient. With this method, the frequency chirp of the harmonics is studied. The fifth harmonic beam (160 nm) is used to experimentally induce nonlinear multiphoton ionisation in the rare gases. This might enable measurement of ultrashort harmonic pulse durations at short wavelengths with an autocorrelation method. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/41919
 author
 Roos, Lena ^{LU}
 opponent

 Dr Potvliege, Robert, Dept. of Physics, University of Durham, South Road, Durham DH13LE, UK
 organization
 publishing date
 2001
 type
 Thesis
 publication status
 published
 subject
 keywords
 Coherent radiation, Optimisation, Multiphoton ionisation, Phase matching, Physics, Fysik, Atomic and molecular physics, Atom och molekylärfysik, Laserteknik, Laser technology, Highpower lasers, Short pulses, Highorder harmonic generation, Short wavelength, Fysicumarkivet A:2001:Roos
 pages
 190 pages
 publisher
 Department of Physics, Lund University
 defense location
 Lecture Hall F, Department of Physics, Sölvegatan 14, Lund, Sweden
 defense date
 20010928 10:15
 external identifiers

 Other:LUTFD2(TFAF1047)1112(2001)
 ISBN
 9163113708
 language
 English
 LU publication?
 yes
 id
 c536f75650ef4502ac69f75a8190fd91 (old id 41919)
 date added to LUP
 20071001 09:33:21
 date last changed
 20160919 08:45:08
@misc{c536f75650ef4502ac69f75a8190fd91, abstract = {The highorder harmonics that are created in the interaction between an intense laser pulse (around 10<sup>14</sup> W/cm<sup>2</sup>) and a gas medium are studied. The highorder harmonic radiation is a relatively new source of coherent radiation in the short wavelength range. The highorder harmonics are interesting for applications because of their good spatial and temporal coherence, their short pulse duration and the possibility to focus the harmonic radiation to high intensity.<br/><br> <br/><br> The first part of this thesis focuses on optimising the highorder harmonic pulse energy. This is motivated by the relatively low conversion efficiency of highorder harmonic generation. These studies are aimed to understand how the conversion efficiency can be improved. The harmonic yield as a function of medium length is studied and the different effects that influence the harmonic yield are discussed. A new geometrical configuration with two collinear foci along the propagation axis is found to improve the harmonic conversion efficiency compared to an ordinary onefocus beam. In addition, theoretical optimisations of the harmonic pulse energy are carried out. With a genetic optimisation algorithm, two or three parameters related to the characteristics of the laser beam and the nonlinear medium are varied simultaneously. Over 10<sup>9</sup> photons per pulse at a wavelength of 28 nm can be obtained.<br/><br> <br/><br> The underlying idea of the second part of this thesis is that the highorder harmonics are potentially suitable for generating pulses of shorter duration than what is possible with current technology. With the genetic algorithm, the temporal properties of the harmonic pulse are optimised theoretically. Harmonic pulse durations as short as 6 fs are obtained, generated by a 50 fs laser pulse. The temporal coherence is optimised by selecting the transformlimited part of the harmonic spectrum. In this condition, the time profile of the harmonic radiation is a train of 265 attosecond long pulses. By experimentally manipulating the ellipticity of the laser pulse in time, one or two temporal gates of a few femtosecond duration can be created where the polarisation is linear and harmonic emission is efficient. With this method, the frequency chirp of the harmonics is studied. The fifth harmonic beam (160 nm) is used to experimentally induce nonlinear multiphoton ionisation in the rare gases. This might enable measurement of ultrashort harmonic pulse durations at short wavelengths with an autocorrelation method.}, author = {Roos, Lena}, isbn = {9163113708}, keyword = {Coherent radiation,Optimisation,Multiphoton ionisation,Phase matching,Physics,Fysik,Atomic and molecular physics,Atom och molekylärfysik,Laserteknik,Laser technology,Highpower lasers,Short pulses,Highorder harmonic generation,Short wavelength,Fysicumarkivet A:2001:Roos}, language = {eng}, pages = {190}, publisher = {ARRAY(0x9408380)}, title = {Optimisation and Application of Intense HighOrder Harmonic Pulses}, year = {2001}, }