I. W. Choi

Dependence of the electron beam parameters on the stability of laser propagation in a laser wakefield accelerator

Characteristics of electron beams produced by the laser wakefield acceleration are presented. The dependence of the electron beam parameters on the laser focal spot size is investigated. The experimental result shows the generation of quasimonoenergetic electron beam although the laser spot size was several times larger than the plasma wavelength. Stable electron beam generation at large laser spots was owing to the stable laser propagation in plasma channels. At a small laser spot, the beam quality is poor and this is attributed to the the filamentation instability of the laser beam.

Simultaneous generation of ions and high-order harmonics from thin conjugated polymer foil irradiated with ultrahigh contrast laser

We report the manufacturing of an (ultra-)thin foil target made of conjugated polymer, poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT), and the simultaneous observation of laser-accelerated ions and second harmonic radiation, when irradiated with ultrahigh-contrast laser pulse at a maximum intensity of 4u2009×u20091019u2009W/cm2. Maximum proton energy of 8 MeV is achieved along the target normal direction. Strong second harmonic with over 6% energy ratio compared to fundamental is emitted along the specular direction. Two-dimensional particle-in-cell simulations confirm the simultaneous generation of protons and high-order harmonics, which demonstrates the feasibility of applications requiring particle and radiation sources at once, effectively using the same laser and target.

Self-mode-transition from laser wakefield accelerator to plasma wakefield accelerator of laser-driven plasma-based electron acceleration

Via three-dimensional particle-in-cell simulations, the self-mode-transition of a laser-driven electron acceleration from laser wakefield to plasma-wakefield acceleration is studied. In laser wakefield accelerator (LWFA) mode, an intense laser pulse creates a large amplitude wakefield resulting in high-energy electrons. Along with the laser pulse depletion, the electron bunch accelerated in the LWFA mode drives a plasma wakefield. Then, after the plasma wakefield accelerator mode is established, electrons are trapped and accelerated in the plasma wakefield. The mode transition process and the characteristics of the accelerated electron beam are presented.

Characteristics of a Ni-like silver x-ray laser pumped by a single profiled laser pulse

We characterized a Ni-like silver soft x-ray laser realized as, what we believe is, a new variant of the grazing incidence pumping (GRIP) scheme. The x-ray laser was pumped by a single profiled laser pulse from a 10 Hz Ti:sapphire laser system. The Ni-like Ag x-ray laser was saturated with a gain coefficient of 76 cm−1 and an effective gain-length product of 28.2. The spatial characteristics of the new version of GRIP x-ray laser are presented including the far- and near-field beam profiles. Computational modeling of the lasing conditions was used to provide some qualitative explanations of the physical processes occurring in the x-ray laser. Additionally, we obtained some preliminary results on the injection seeding technique applied to the Ni-like Ag active medium using the 59th harmonic of the Ti:sapphire laser pulse as the seed. The single-pulse variant of the pumping scheme proved to be a stable and simple configuration of the table-top x-ray lasers also suitable for the injector-amplifier arrangement.

Proposed hole-target for improving maximum proton energy driven by a short intense laser pulse

By using particle-in-cell simulations, a new method for energetic collimated proton generation via intense short pulse laser-thin foil interactions is presented. To enhance the electron heating efficiency, a small hole is bored at the center of a thin foil target. The small hole combines target heating mechanisms effectively, which results in a high proton maximum energy. While an ultraintense, ultrashort laser pulse propagates through a small hole (diameter<laser spot size), the laser pulse drives electrons pulled out from the hole inner wall effectively inside the hole. When these electrons leave the target, a strong sheath field is formed between the electrons and the target rear surface and this accelerates protons from the rear surface of the target. The effective combination of the laser longitudinal ponderomotive force with the transverse heating (by E field) mechanism results in highly efficient electron heating of the hole target. When the rear part of the hole is filled with a proton-electron co...

Laser-driven electron beam acceleration and future application to compact light sources

Laser‐driven plasma accelerators are gaining much attention by the advanced accelerator community due to the potential these accelerators hold in miniaturizing future high‐energy and medium‐energy machines. In the laser wakefield accelerator (LWFA), the ponderomotive force of an ultrashort high intensity laser pulse excites a longitudinal plasma wave or bubble. Due to huge charge separation, electric fields created in the plasma bubble can be several orders of magnitude higher than those available in conventional microwave and RF‐based accelerator facilities which are limited (up to ∼100 MV/m) by material breakdown. Therefore, if an electron bunch is injected into the bubble in phase with its field, it will gain relativistic energies within an extremely short distance. Here, in the LWFA we show the generation of high‐quality and high‐energy electron beams up to the GeV‐class within a few millimeters of gas‐jet plasmas irradiated by tens of terawatt ultrashort laser pulses. Thus we realize approximately fo...

Radiography with Low Energy Protons Generated from Ultraintense Laser-plasma Interactions

In order to obtain high quality images of thin objects, we performed an experiment of proton radiography by using low energy protons generated from the interaction of an ultrashort ultraintense laser with solid targets. The protons were produced from a thin polyimide target irradiated by the laser pulse, and their maximum energy was estimated at up to 1.8 MeV. A CR-39 nuclear track detector was used as a proton radiography screen. The proton images were obtained by using an optical microscope and the spatial resolution was evaluated by a Modulation Transfer Function (MTF). We have achieved about

On the Way Towards a High Repetition Rate X-Ray Laser

10;{mu}m

Projection imaging with directional electron and proton beams emitted from an ultrashort intense laser-driven thin foil target

spatial resolution of images. The obtained spatial resolution shows about

Secondary source generation using 30-fs, PW Ti:sapphire laser (PULSER)

4{sim}5