报告题目：Laser-driven Electron Accelerator via Ionization Injection and Multiple Laser Beams
In recent years we have been conducting a variety of laser-plasma acceleration experiments using ultrashort (30 fs) 30 TW, 60 TW and up to 120 TW laser pulses. We have performed two types of laser wakefield acceleration (LWFA) experiments; the first one was based on the self-injection of electrons into a 30 TW laser-driven helium plasma wave generated in 4 mm-long gas jet (a0 ~1.2). We observed ~120 MeV electron beams with ~ 40 % energy-spread (FWHM) . In order to enhance the quality of the observed electron beams, we conducted a series of experiments where we employed the so-called “ionization-injection” mechanism (for the same laser parameters ~ 30 TW), and we observed a significant enhancement of the electron beam energy up to > 400 MeV and a narrowing of the energy-spread below 4% [2, 3]. In a follow up research on ionization injection, and in order to further boost the electron accelerator energy and quality, we employed 120 TW laser pulses and 1 cm-long gas jet. Here we observed narrow energy-spread beams (7 %) with 1.2 giga-electron volts peak energy . Our experimental results and the involved physics were verified by 3D-PIC simulations using OSIRIS code. We realized that the version of ionization injection we employed exhibits a self-truncation after an initial electron bunch injection at the beginning of the laser-plasma interaction. We believe that a further exploration of this regime using PW laser pulses may lead to the generation of electron beams of several GeV energies while preserving the narrow energy-spread features, that would be an important step towards realization of a table-top X-ray free electron laser (X-FEL). Finally, and since 2017, we have been conducting experimental research on the so-called “two-colour laser wakefield acceleration” which employs two 800 nm and 400 nm co-propagating relativistic laser pulses in the plasma, where we observed more interesting results . In my talk, these results will be discussed in detail.
Nasr Hafz is an EGYPTIAN physicist who received his B.Sc. in “Physics” from Ain Shams University in Cairo in 1991. From 1993 to 1998 he was employed as a Junior faculty in Plasma Physics by Egypt’s Atomic Energy Authority. He moved to Tokyo, JAPAN in 1998 and was awarded a Ph. D. in Engineering “Quantum Engineering and Systems Science” from the University of Tokyo in 2001. From 2002 to 2011 he was a Staff Senior Research Scientist at GIST in South Korea. From 2011 to mid-2018 he was a Tenure-track Faculty with the Department of Physics and Astronomy of Shanghai Jiao Tong University, CHINA. Since Sept. 2018 he is a Leading Scientist and Leader of the Electron Acceleration Group at ELI-ALPS, HUNGARY, EU. His main task at ELI-ALPS within the new few years is to establish two high-repetition rate (10 Hz and 1 kHz) laser accelerator beamlines based on ELI’ unique laser systems for applications in science and technology.
Nasr’s research is focusing on electron acceleration using TW lasers and plasmas and the generation of secondary radiations and particles. He has supervised/co-supervised 12 Ph.D. students over the past 7 years alone. He has authored and co-authored 62 peer- reviewed articles some of them appeared in “Nature Photonics, PNAS, Scientific Reports”, and others. He also has 60 invited talked, lectures and conference proceedings.