Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium PDF
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Springer Theses Recognizing Outstanding Ph.D. Research Cheng Jin Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium Springer Theses Recognizing Outstanding Ph.D. Research For furthervolumes: http://www.springer.com/series/8790 Aims and Scope The series ‘‘Springer Theses’’ brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected for its scientific excellence and the high impact of its contents for the pertinent fieldofresearch.Forgreateraccessibilitytonon-specialists,thepublishedversions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explaining the special relevance of the work for the field. 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Cheng Jin Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium Doctoral Thesis accepted by Kansas State University, USA 123 Author Supervisor Dr. ChengJin Prof.Chii-Dong Lin Department of Physics Department of Physics Kansas State University Kansas State University Manhattan, Kansas Manhattan, Kansas USA USA ISSN 2190-5053 ISSN 2190-5061 (electronic) ISBN 978-3-319-01624-5 ISBN 978-3-319-01625-2 (eBook) DOI 10.1007/978-3-319-01625-2 SpringerChamHeidelbergNewYorkDordrechtLondon LibraryofCongressControlNumber:2013945805 (cid:2)SpringerInternationalPublishingSwitzerland2013 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodology now known or hereafter developed. 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While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) List of publications during Ph.D. thesis work1 [1] C. D. Lin, Cheng Jin, Anh-Thu Le, and R. R. Lucchese. Probing molecular framephotoelectronangulardistributionsviahigh-orderharmonicgeneration from aligned molecules. J. Phys. B 45, 194010 (2012). [2] Guoli Wang, Cheng Jin, Anh-Thu Le, and C. D. Lin. Conditions for extracting photoionization cross sections from laser-induced high-order- harmonic spectra. Phys. Rev. A 86, 015401 (2012). [3] ChengJinandC.D.Lin.Comparisonofhigh-orderharmonicgenerationof Ar using truncated Bessel and Gaussian beams. Phys. Rev. A 85, 033423 (2012). [4] W. Cao, G. Laurent, Cheng Jin, H. Li, Z. Wang, C. D. Lin, I. Ben-Itzhak, andC.L.Cocke.Spectralsplittingandquantumpathstudyofhigh-harmonic generation from a semi-infinite gas cell. J. Phys. B 45, 074013 (2012). [5] Cheng Jin, Julien B. Bertrand, R. R. Lucchese, H. J. Wörner, Paul B. Corkum, D. M. Villeneuve, Anh-Thu Le, and C. D. Lin. Intensity dependence of multiple-orbital contributions and shape resonance in high- orderharmonicgenerationofalignedN molecules.Phys.Rev.A85,013405 2 (2012). [6] C. Trallero-Herrero, Cheng Jin, B. E. Schmidt, A. D. Shiner, J.-C. Kieffer, P. B. Corkum, D. M. Villeneuve, C. D. Lin, F. Légaré, and A. T. Le. Generation of broad XUV continuous high harmonic spectra and isolated attosecond pulses with intense mid-infrared lasers. J. Phys. B (fast track communication) 45, 011001 (2012). [7] Guoli Wang, Cheng Jin, Anh-Thu Le, and C. D. Lin. Influence of gas pressure on high-order-harmonic generation of Ar and Ne. Phys. Rev. A 84, 053404 (2011). [8] Cheng Jin, Anh-Thu Le, Carlos A. Trallero-Herrero, and C. D. Lin. Generation of isolated attosecond pulses in the far field by spatial filtering with an intense few-cycle mid-infrared laser. Phys. Rev. A 84, 043411 (2011). [9] Cheng Jin, Hans Jakob Wörner, V. Tosa, Anh-Thu Le, Julien B. Bertrand, R. R. Lucchese,P. B. Corkum,D. M. Villeneuve,and C. D. Lin. Separation of target structure and medium propagation effects in high-harmonic generation. J. Phys. B 44, 095601 (2011). 1 Mostpartsofthisthesishavebeenpublishedin[3,5,8,9,10,12,16,18]. [10] Cheng Jin, Anh-Thu Le, and C. D. Lin. Analysis of effects of macroscopic propagation and multiple molecular orbitals on the minimum in high-order harmonic generation of aligned CO . Phys. Rev. A 83, 053409 (2011). 2 [11] Song-Feng Zhao, Cheng Jin, R. R. Lucchese, Anh-Thu Le, and C. D. Lin. High-order-harmonic generation using gas-phase H O molecules. Phys. 2 Rev. A 83, 033409 (2011). [12] ChengJin,Anh-ThuLe,andC.D.Lin.Mediumpropagationeffectsinhigh- order harmonic generation of Ar and N . Phys. Rev. A 83, 023411 (2011). 2 [13] Song-Feng Zhao, Junliang Xu, Cheng Jin, Anh-Thu Le, and C. D. Lin. Effect of orbital symmetry on the orientation dependence of strong field tunneling ionization of nonlinear polyatomic molecules. J. Phys. B 44, 035601 (2011). [14] Song-Feng Zhao, Cheng Jin, Anh-Thu Le, and C. D. Lin. Effect of an improved molecular potential on strong-field tunneling ionization of molecules. Phys. Rev. A 82, 035402 (2010). [15] Song-Feng Zhao, Cheng Jin, Anh-Thu Le, T. F. Jiang, and C. D. Lin. Determination of structure parameters in strong-field tunneling ionization theory of molecules. Phys. Rev. A 81, 033423 (2010). [16] Cheng Jin, Anh-Thu Le, Song-Feng Zhao, R. R. Lucchese, and C. D. Lin. Theoretical study of photoelectron angular distributions in single-photon ionization of aligned N and CO . Phys. Rev. A 81, 033421 (2010). 2 2 [17] Song-Feng Zhao, Cheng Jin, Anh-Thu Le, T. F. Jiang, and C. D. Lin. Analysisofangulardependenceofstrong-fieldtunnelingionizationforCO . 2 Phys. Rev. A 80, 051402 (2009). [18] Cheng Jin, Anh-Thu Le, and C. D. Lin. Retrieval of target photorecombi- nation cross sections from high-order harmonics generated ina macroscopic medium. Phys. Rev. A 79, 053413 (2009). [19] Van-Hoang Le, Ngoc-Ty Nguyen, C. Jin, Anh-Thu Le, and C. D. Lin. Retrieval of interatomic separations of molecules from laser-induced high- order harmonic spectra. J. Phys. B 41, 085603 (2008). Supervisor’s Foreword The interaction of light with matter is a common method for uncovering the microscopic structure of a material in the physical world. Light sources over the whole electromagnetic spectrum are used to ‘‘see’’ different aspects of an object. With the invention of infrared and visible lasers since the 1960s, it has long been possible to generate other lights in the nearby spectral range, using second har- monics or third harmonics, via the nonlinear interaction of lasers with suitable materials. As the laser technology advances, ultrashort high-power infrared lasers can now be focused into an even smaller volume to create electric fields that are comparableorgreaterthanthetypicalelectricfieldseenbyanelectroninanatom. For more than 20 years, high-order harmonics (HH) with energies in the tens to hundreds times of the energy of the infrared photon have been generated when intense lasers are focused into a gas medium. These light pulses extend from the extreme ultraviolet to soft X-rays. With suitable filters, these harmonics offer potentiallyusefultabletoplightsourcesoverabroadspectralregion.Furthermore, theemittedharmonicsarecoherent.Theycanalsobesynthesizedtoformisolated attosecond pulses or attosecond pulse trains. Today these attosecond pulses are being used to study the dynamics of atoms, molecules and condensed media, to interrogate their evolution at the femto- and atto-second timescales. High-order harmonics are generated by the coherent nonlinear interaction of intense infrared lasers with atoms and molecules in the gas phase. The basic principleforthegenerationofhighharmonicsfromeachatomormoleculeisvery simple. Near the peak of the laser field in each half optical cycle, an electron is ripped offfrom the atom or molecule. This electron is thrown into the oscillating electric field of the laser and later it may be driven back to recollide with the atomicormolecularionleftbehind.Iftheelectron,whichhasbeenacceleratedby thelaserfield,recombineswiththeion,thentheexcessivekineticenergygainedin the laser field is released in the form of a high-energy photon. This seemingly simplepictureexplainstheemissionofharmonics,butformorethantwodecades it has not been possible to carry out accurate theoretical calculations that can be compared to harmonic spectra observed experimentally. Without a quantitative theory,effortstoenhancetheyieldsofharmonicsinthelaboratoryhavetodepend on experimentation alone. This has slowed down the progress of making HH for practical applications as a useful light source. vii viii Supervisor’sForeword High harmonics observed in the laboratory are generated from the coherent emission of harmonics from all the gas atoms or molecules as the intense laser propagates through the gas medium. In turn, the intense laser is modified by the gas medium as it propagates. To achieve high brightness for the harmonics, favorablephasematchingconditionsshouldbemet.Thisisachievedbyadjusting laserfocusingconditions,gasjetposition,gaspressure,anddegreesofionization. To account for all of these effects, it is necessary to develop a computer software packagethatcansimulatethegeneratedharmonicspectra.Thisgoalwasachieved by Cheng Jin, and this project forms the basis of his Ph.D. thesis. In his thesis work, Cheng first studied harmonics generated on atomic targets. He was able to show that the harmonic spectra of Ar atoms from the theoretical simulation match very well with the measured ones. Later, he extended the sim- ulations to molecular targets, for molecules that are randomly distributed or par- tially alignedinspace.Hewasalsoabletoshowthatharmonicscan begenerated from electrons thatare ionized from the inner orbitals ofthe molecule when laser intensity is increased. For the first time, harmonic spectra measured in the labo- ratory can be accurately reproduced by theoretical simulations. To make such comparisons, interactions with experimentalists are essential since the experi- mental conditions are required for the simulation. His work establishes a new standard for the theoretical studies of high-order harmonic generation. It is no longer reasonable to study harmonic generation without considering propagation effects. After more than two decades, the details of harmonic generation in a gas medium can finally be simulated theoretically in view of Cheng’s work. TheimpactoftheresearchcarriedoutbyChengJinwillbefar-reachinginthe coming years as experimentalists are pushing harmonic generation to higher energies, with the goal of generating soft X-rays in the water window region or even hard X-rays. For this purpose, mid-infrared long-wavelength driving lasers (2–5microns) are beingused. Because the harmonic yields droprapidlyfor long- wavelengthlasers,usefullightsourcesforsoftandhardX-rayscanbecomereality and will have to depend on whether favorable phase-matching conditions with high gas pressure can be identified, or whether one can engineer synthesized waveform to enhance harmonics generated by individual atoms. In either endea- vor,realisticsimulationswithmid-infraredlaserswillbeneeded.Thethesiswork ofChengJinwillserveasagreatstartingpointforyoungresearcherstoenterthis excitingfield,tochallengetheobstaclesthatonehastofaceinordertorealizethe goal of using harmonic generation as an all-purpose tool for new tabletop light sources. Manhattan, Kansas, USA, June 2013 Prof. Chii-Dong Lin Acknowledgments First, I would like to sincerely thank my advisor, Dr. Chii-Dong Lin for his guidance, encouragement, and support all through my Ph.D. study. I am really grateful that he brings me to this exciting research field, constantly motivates me andgivesmetheinvaluableadvice.Istillremember themostdifficulttimeinmy project. The propagation code was working at the low gas pressure, however, it didn’t work at the high gas pressure. I could not figure out problems for a few months, and even wanted to give up. His patience and encouragement helped me going through that time. I also have learned a lot from my advisor about how to conduct the effective research and how to grab a hot topic in the field. This valuable experience will be helpful for my future life. IwouldliketothankDr.Anh-ThuLeforhiscontinuoushelpsinceIfirstjoined Prof. Lin’s group. I have learned from him to run and write some computation programmes, which soon became an essential part in my project. He is always available for stimulated discussions, and helping me understand every concept in the field. Next I would like to give my appreciations to other members, former and current,in Prof. Lin’sgroup. Dr. Rui-Hua Xie, with whom I was closely working intheverybeginningofmyproject,taughtmestepbysteptodotheprogramming and build up basic research tools. Dr. Turker Topcu initiated the propagation project, and nicely shared with me his experience gathered from successful and unsuccessful attempts. This was really useful and important for me to start a new project.Dr.ZhangjinChenhadbeenhelpingmeinbothresearchandlifeformany years. Dr. Toru Morishita gave me the permit to use his TDSE code, and helped me in numerical algorithm. Dr. Song-Feng Zhao had been my collaborator in the projectofthetunnelingionizationofmolecules,which isanimportantpartinmy project.Hekindlyprovidedmewithnecessarydataformyproject.Andwehada lot of good discussions in many interesting issues. I also have collaborated with Dr. Guoli Wang inthe propagation project. I have been benefited from his efforts to investigate propagation effects under some extreme conditions, such as high intensity and high pressure. I appreciate my class fellow Junliang Xu, who is an intelligentandacarefulresearcher,forhishelpandcollaborationincoursestudies. Dr. Wei-Chun Chu and Dr. Allison Harris discussed with me about some inter- esting problems. I really enjoyed these discussions. ix
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