Program

場所：電気通信大学　東６号館８階　８０３　会議室


14:00-14:40
Oleg. I. Tolstikhin, “Kurchatov” Institute & MIPT, Russia
"Adiabatic theory of ionization of atoms by intense laser pulses''

ABSTRACT
The adiabatic theory of ionization of atoms by intense few-cycle laser pulses is developed. This theory rests on a single parameter eps giving a ratio of the atomic and laser time scales and ecomes exact in the limit eps->0 uniformly with respect to the amplitude of the laser pulse. Its comparison with the strong-field approximation is discussed.

14:40-15:10
Linda Hamonou, University of Electro-Communucasions
Calculation of Siegert states in electric field : from atoms to molecules"

ABSTACT
In order to study harmonic generation in molecules, we want to create a molecular code able to solve the stationary Schrödinger equation in electric field. Calculation of Siegert state has  already been performed accurately for atoms. In this talk I will briefly define harmonic generation before describing the main features included in the atomic code to obtain energies and ionization rates of Siegert states. I will then finish by explaining the changes necessary in the program to be able to treat molecular problems.

15:30-16:00
Chiennan Liu, Fu-jen Catholic University, Taiwan
"Some　aspects of He in intense laser fields"

ABSTRACT
I will report on the progress of two current projects. One is our theoretical analysis on the recent helium photoionization measurements using free-electron laser. The other project focuses on probing the molecular modes of helium doubly excited states. By analyzing the photoionization
spectra, we explore the possibility of a pump-probe scheme for these molecular like modes using an x-ray pulse combined with an IR field.

16:00-16:30
Minghui Xu, Peking University, China
"Laser-assisted photoionization of atoms by attosecond pulse"

ABSTRACT
Conventional strong-field processes are initiated by coherently transferring a part of the boundstateelectron wavefunction to the continuum via tunneling ionization, and then the freed electron wavepackets (EWPs) are subsequently accelerated by the laser field. The interaction of these EWPs with their parent ion gives rise to processes such as high-order harmonic generation and above threshold ionization (ATI). Furthermore, strong-field ionization has recently attracted increasing interest as a probe of the atomic and molecular structure [1, 2]. However, the creation and acceleration of the EWPs are governed by the same laser pulse, which will greatly limit the flexibility of further controlling the electron dynamics.

In the laser dressed attosecond photoionization [3], on the other hand, EWPs are produced by isolated attosecond pulse. Thus the energy, timing and coherence of the EWPs can be varied independently of the synchronized laser field, which will drive their subsequent dynamics. The decoupling of the creation and acceleration of the EWPs will offer a much better route to measuring and controlling the dynamics of continuum electrons [4].

[1] M. Meckel, et.al, Science 320, 1478 (2008).
[2] R. Gopal, et.al, Phys. Rev. Lett. 103, 053001 (2009).
[3] L.-Y. Peng, et.al, New J. Phys. 10, 025030 (2008).
[4] T. Remetter, et.al, Nature Phys. 2, 323 (2006).

日時：平成２２年７月６日(火）午後（日程変更になりました）
場所：電気通信大学　東６号館８階　８０３　会議室


14:00-14:40
Kenichi L. ISHIKAWA, Photon Science Center, School of Engineering, The University of Tokyo
"Quantum-Path Interference in High-Harmonic Generation and Optical-Field Ionization"

ABSTRACT

In this talk, we discuss the role of quantum-path interference in the wavelength dependence of high-harmonic generation (HHG) and optical-field ionization (OFI), which is attracting an increasing interest due to recent development of high-power mid-infrared laser systems.
　　　In the first part, we present the dependence of the intensity of radiation due to high-harmonic generation as a function of the wavelength l of the fundamental driver field. Superimposed on smooth power-law dependence, we find surprisingly strong and rapid fluctuations on a fine l scale. We identify the origin of these fluctuations in terms of quantum path interferences with many returning orbits significantly contributing.
　　　In the second part, within a semiclassical description of above-threshold ionization (ATI), we identify the interplay between intracycle and intercycle interferences. The former is imprinted as a modulation envelope on the discrete multiphoton peaks formed by the latter. This allows one to unravel the complex interference pattern observed for the full solution of the time-dependent Schrödinger equation in terms of diffraction at a grating in the time domain. These modulations can be clearly seen in the dependence of the ATI spectra on the laser wavelength. Shifts in energy modulation result from the effect of the long Coulomb tail of the atomic potential.

14:40-15:20

Liang-You Peng, Peking University, China
"Tracing and steering electron motion inside atoms and molecules by attosecond pulses"

ABSTRACT
The availability of attosecond pulses has opened a drastically new regime of ultrafast sciences, where it is possible for scientists to trace and control the motion of electrons on its natural spatial and temporal scale. After the fruitful developments of femtosciences in the last two decades, the newly opened attosecond science is another big jump of human being to understand and control the internal dynamics of atoms and molecules. In this seminar, I will talk about the tracing the electron hopping inside molecules and the electron correlation dynamics of He by attosecond pulses.  Our results are based on accurate solution of the relevant time-dependent Schroedinger equation.

15:20-15:40 Break

15:40-16:10

Zheng Zhang, Peking University, China
"Traces of the electron correlations in two-photon double ionization"

By solving the full-dimensional time-dependent Schrodinger equation for helium, we are able to investigate the electron correlation dynamics during double ionization process. By analyzin different energy spectra when two eletrons are ejected towards different directions, we clearly identified the Coulomb repulsion effects in final state when electrons are ejected into the same hemisphere. Our full-dimensional results confirm the anticipations in previous low-dimensional calculations.

[1] Z. Zhang, L. Y. Peng, Q. H. Gong, and T. Morishita, Optics Express, 18, 8976 (2010)

16:10-16:40
Toshihito Umegaki, University of Electro-Communucasions
Analysis of high-order harmonic spectra of argon atoms by intense $\omega$-2$\omega$ laser pulses

ABSTRACT
We analyzed the high-order harmonic spectra by intense $\omega$-2$\omega$ laser pulses polarized perpendicularly each other with 800- and 400-nm wavelength, respectively. We calculated the high-order harmonic spectra by solving the time-dependent Schrödinger equation, and compared with corresponding experimental results in a case of the laser intensity with about 0.1 PW/cm2. We also evaluated corresponding classical trajectories.

16:40-17:10
Haruhide Miyagi, University of Electro-Communucasions
"Scattering theory for accurate calculation of ATI spectra of diatomic molecules by intense lasers"

ABSTRACT
The time-independent scattering theory for two-center Coulomb system on the prolate spheroidal coordinate is an essential part of accurate calculation of ATI spectra of the laser ionization of an H$_2^+$ molecule. However, this theory is not familiar to the recent researchers. It seems to be a lost art because there exist only a few old papers about this theory. In this talk, therefore, I will explain the scattering theory on the prolate spheroidal coordinate in detail and derive the explicit expressions of the wave function of the scattering state and the scattering amplitude. I will show several numerical results obtained currently.