* PHYSICS/BK21 SEMINAR *

Manipulating electron dynamics in waveform-controlled two-color laser fields

연사: Dr. Ya Cheng[Shanghai Institute of Optics and Fine Mechanics]

일시: 2007 년 9 월 3 일 15:00

장소: 물리학과 세미니실(3-201호)

ABSTRACT:

In the classical picture of high-order harmonic generation (HHG), an electron is first tunnel-ionized at peak of an electric field, and then is accelerated outward from its parent ion until the laser field reverses its direction. After that, the electron is driven back to the ion and recombines with the ion through the release of an XUV photon [1]. The system composed of the atom and the driving laser field is incredibly similar to a microscopic X-ray tube where electrons are first accelerated to high energy by an electric field and then collide with a solid target [2]. Therefore, in order to optimize the HHG process, it is crucial to precisely control the electron dynamics in the light field, such as the ionization, acceleration, and recombination, which are completely determined by the light waveform. From theoretical point of view, generation of arbitrary light waveform can be realized by Fourier synthesis of optical pulses whose frequencies span a broad spectrum. However, this approach is still technically too difficult at present. We will show that, in a general sense, one can effectively control the light waveform using two-color laser fields. In particular, our interest is focused on the optimization of the waveform of few-cycle light field. We demonstrate that isolated single sub-100as extreme ultraviolate (XUV) pulse can be efficiently generated via HHG process by adding a phase-delayed, weak second-harmonic wave upon a few-cycle driving pulse [3]; and high energy photons and electrons as well as tunable XUV coherent radiation can be obtained by adding a weak sub-harmonic wave on the few-cycle pulse [4]. Moreover, quantum path control in few-cycle regime is achievable using these synthesized two-color driving pulses [4]. Some of the theoretical predictions have been proved by recent experiments.

문의처: 김동언(054-279-2089, kimd@postech.ac.kr)