TUNNELING IONIZATION OF NOBLE GAS ATOMS USING A HIGH INTENSITY LASER AT 1 prn WAVELENGTH by Stcven Jay Augst Submitted in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY Supervised by David D. Meyerhofer and J. H. Eberly Department of Physics and Astronomy and College of Arts and Science University of Rochester Rochester, New York 1991
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TUNNELING IONIZATION OF NOBLE GAS ATOMS USING A …Laser induced ionization of noble gases has been studied with a 1-ps, 1-prn laser. An experimental survey of the intensity dependence
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TUNNELING IONIZATION OF NOBLE GAS ATOMS USING A HIGH
INTENSITY LASER AT 1 prn WAVELENGTH
by
Stcven Jay Augst
Submitted in Partial Fulfillment
of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
Supervised by David D. Meyerhofer
and J. H. Eberly
Department of Physics and Astronomy
and College of Arts and Science
University of Rochester
Rochester, New York
1991
CURRICULUM VITAE
Steven Jay Augst was born on January 23, 1963 in Menahga, Minnesota He
attended Gustavus Adolphus College from 198 1 to 1985 when he graduated Magna
Cum Laudc with a B.A. degree in Physics. From 1985 to 1991 he attended the
University of Rochester as a graduate student in the department of Physics and
Astronomy where he was the recipient of a three year Rush Rhees fellowship. His
research work was performed at the Laboratory for Laser Energetics under the
supervision of David D. Meyerhofer.
Y. H. Chuang, D. D. Meyerhofer, S. Augst, H. Chen, J. Peaaoss, and S. Uchida, "Suppression of the Pedestal in a Chirped-Pulse-Ampiification Laser," J. Opt. Soc. Am. B. 8, 1226 (199 1).
S. Augst, D. D. Meyerhofer, J. Peaaoss, and C. I. Moore, "Spatial dismbution of high-order harmonics generated in the tunneling regime", in the Proceedings of Short- Wavelength Coherent Radiation: Generaion and Applicanon (OSA topical meering), Monteny, CA April 1991 (pub. by OSA, Washington D. C.,
199 1). S. Augst, D. D. Meyerhofer, D. Strickland, and S. L. Chin, "Laser Ionization of
Noble Gases by Coulomb-Barrier Suppression," J. Opt. Soc. Am. B. 8, 858
(1991). S. Augst, D. D. Meyerhofer, C. I. Moore, and J. Peaaoss, "Tunneling Ionizarion and
Harmonic Generation in Krypton Gas using a High-Intensity, 1 - ~ m , 1-ps
Laser", in the Proceedings of SPIE OWLASE '90, Femtosecond to
Nanosecond High-Inremiry Losers and Applicarionr, 1229, 152 (pub. by SPIE, Belligham, WA, 1990).
S. Augst, D. Smckland, D. D. Meyerhofer, S. L. Chin and J. H. Eberly, "Tunneling
Ionization of Noble Gases in a High-Lntensity Laser Field," Phys. Rev. Lett.
63, 2212 (1989).
ACKNOWLEDGMENTS
I would like to thank Dr. David Meyerhofer for providing daily supenision and
insightful discussions regarding experiments and the analysis of the data which was
obtained. I would also like to thank Dr. Joseph Eberly for being my official advisor
and for providing many critical readings of publications and this thesis. I would also
like to thank Dr. See-Leang Chin who initiated the ionization experiments at the
Laboratory for Laser Energetics when he was a visiting professor at the University of
Rochester. He provided many fruitful discussions and much encouragement.
Dr. Robert Kremens provided extensive help and guidance throughout the
course of my graduate career. His philosophy regarding scientific research was both
helpful and at times entertaining. Without his expertise many of these experiments
would not have been completed.
The assistance of several other graduate students was also greatly appreciated.
Among these arc: Yung-Ho Chuang who taught me much about lasers and who refined
the original laser system design so that it did not require constant supervision, Justin
Peaaoss who traded shifts with me when we did 16 hour data runs and let me borrow
his computer to write this thesis, Chris Moore who did vimally a l l the analysis of the
harmonic generation experiments (which are not discussed in this thesis), and Shigeaki
Uchida and Hong Chen for numerous helpful suggestions and discussions. - The original laser system was designed and built by Dr. Donna Strickland,
Pamck Maine, and Dr. Gerard Mourou. I would like to thank them for the use of this
laser.
Lastly, I grcady appreciate the support of the staff at the Laboratory for Laser
Energetics. This work was supported by the National Science Foundation under
contract No. PHY 8822730. Additional support was provided by the U.S.
Depanment of Energy Division of Inertial Fusion under agreement No. DE-FC03-
85DP40200 and by the Laser Fusion Feasibility Project at the Laboratory for Laser
Energetics which has the following sponsors: Empire State Electric Enagy Research
Corporation, New York State Energy Research and Development Authority. Ontario
Hydro, and the University of Rochester.
ABSTRACT
Laser induced ionization of noble gases has been studied with a 1-ps, 1-prn
laser. An experimental survey of the intensity dependence for ion production is
presented for a large number of charge states. The survey spans intensities from
1014 W/cm2 to mid-1016 W/cmZ, which exceeds the intensities of previous surveys at
this wavelength by over an order of rnagnitu&.
The ion production is compared to several theoretical models. Tunneling (or
field-ionization) models rather than multiphoton models describe the data best, and the
two models that have the most satisfactory agreement arc: 1) a one-dimensional
Coulomb barrier suppression model, and 2) a species dependent quasiclassical
tunneling model. The Iff ionization rate dependence which is predicted by lowest-ordcr
perturbation theory is not observed for 1 ps laser pulses. Various forms of Keldysh's
model cannot accurately describe the ionization of all the charge states. Two Thomas-
Fermi models show varying degnes of agreement with the data
Experiments comparing linearly and circularly polarized light suggest that the
ionization process is non-resonant with this wavelength and in this intensity regime.
This is in contrast to some previous experiments at shorter wavelengths which suggests
that all ionization is resonant. Two resonance criteria are suggested, both of which
place the shorter wavelength experiments in the resonance regime and our longer, 1 -pm
wavelength experiments in the non-resonant regime. The two suggested criteria for
resonance both have a strong frequency dependence which explains the transition to
non-resonant ionizazon with our 1 -pm wavelength.
TABLE O F CONTENTS
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