Terahertz emission from a plasma dipole oscillation

허민섭,Kumar Manoj,Song Hyung Seon,Kang Teyoun 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.8

We studied an unrevealed characteristic of radiation emission from a localized plasma oscillator (plasma dipole oscillation— PDO). PDO is a novel concept of generating terahertz emission from a laser plasma-based system. The electromagnetic field generated by a PDO embedded in a uniform plasma, instead of being cut off by the ambient plasma as expected by a common but misleading sense, propagates long distances to escape the plasma eventually. The PDO-THz, differently from other laser plasma-based THz sources, utilizes the collective behavior of the plasma (plasma oscillations) and, accordingly, produces a quasi-narrow-band emission, which can potentially be useful in THz-based accelerator or THz-pump and probe experiments. We verified the PDO mechanism by using realistic three-dimensional particle-in-cell simulations.

Envelope-Kinetic Method for the Simulation of Raman Backward Laser Amplification in a Plasma

허민섭,석희용 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I

A new envelope-kinetic method for the simulation of Raman backscattering and laser amplification is presented. In the new scheme, the plasma wave envelope is obtained from the envelope-kinetic equation. For the self-consistent calculation of the kinetic term, a set of test particles is employed, and their motion is traced. The benchmark results of the new scheme against the averaged particle-in-cell (aPIC) show quite reasonable agreement while the computation speed increases by a factor of more than 10, depending on the parameters.

Investigation of the Optimal Condition for High Acceleration Efficiency in the Laser Wake-Field Acceleration

Heesu Roh,이해준,허민섭 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2

The effects of various laser and plasma parameters on laser wake-field acceleration have been investigated with a two-dimensional particle-in-cell simulation utilizing a moving window. The dynamics of an injected electron beam and the acceleration efficiency are reported for various driving lasers and beam parameters. The injection position of the electron beam and the initial intensity of the laser pulse have specific optimal values to enhance the acceleration efficiency. In the investigated parameter region, which yields no strong effect of the electron beam on the laser wake field, the acceleration efficiency increases with the total charge and with the initial energy of the electron beam. Also, the acceleration efficiency decreases with the incident angle of the electron beam with respect to the direction of laser propagation.

Bunching of Electron Beams by Ultra-Relativistic Laser Pulses

Victor V. Kulagin,석희용,허민섭,Vladimir A. Cherepenin 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.4

The bunching of an electron beam by an ultra-relativistic laser pulse in vacuum is considered. The one-dimensional theory describing this process is elaborated. The laser pulse is shown to compress the electron beam and to generate fast density modulations (microbunching) in it. Two spatial harmonics can be present simultaneously in longitudinal density modulations of the electron beam - one with the laser wavelength and the other with half of the laser wavelength, and the ratio of the amplitudes of the harmonics depends on the duration of the laser pulse front. The average density of the electron beam (slow density modulation) can be controlled by changing the form of the laser pulse envelope. The number of microbunches in the compressed electron beam can be changed by varying the amplitude of the laser pulse and the initial length of the electron beam, and for certain conditions, only one electron bunch with an attosecond length can be produced. The results of the theory are compared with 1D PIC (Particle-In-Cell) simulations, and a good agreement is found.O?

Large transverse motion and micro-bunching of trapped electrons in a wakefield accelerator driven by temporally-asymmetric laser pulses

Han Sup Uhma,남인혁,허민섭,석희용 한국물리학회 2013 Current Applied Physics Vol.13 No.4

The transverse oscillatory motion of trapped electrons under the influence of the laser fields trailing the temporally-asymmetric driving laser pulse was investigated with a theoretical model of the quasi-steady state solution of trapped electron dynamics in the cavity. Our studies show that the transverse oscillation of electrons accelerated in the ion cavity can increase drastically due to the resonance with the laser field of the tail of the temporally-asymmetric pulse. The motion of the accelerated electrons can be represented by a forced harmonic oscillation and it was confirmed by 2D particle-in-cell simulations. These transverse oscillations of beams lead to micro-bunching as well, which can be used for generation of femtosecond coherent radiations of keV range photon energies.

Attosecond Relativistic Electron Beam by Using an Ultrashort Laser Pulse and a Thin Plasma Layer

Victor V. Kulagin,석희용,허민섭 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I

Attosecond ($10^{-15}$ s) electron beams will have some important applications in physics, chemistry, material science, {\it etc.}, where ultrafast phenomena play an important role. Hence, how to generate such ultrashort electron beams is an important issue. Here, we propose to use a thin plasma layer illuminated normally by an ultra-intense femtosecond laser pulse having a sharp rising edge (rising time $\sim$ laser oscillation period). In this process, the plasma layer is compressed nonadabatically by the laser pulse, and all electrons are synchronously accelerated to ultra-relativistic velocities by several half-cycles of the laser field. In an experiment, a solid nanofilm, a taped electron beam, or a thin gas jet can be used as possible targets. For these types of targets, we show the generation of an attosecond high-energy electron beam by using particle-in-cell (PIC) simulations.

Control of the charge and energy of the proton beams from a laserdriven double-layer target

김영국,조명훈,박형주,정문연,허민섭 한국물리학회 2015 Current Applied Physics Vol.15 No.8

Control of the proton beam charge and energy in a laser-driven double-layer target was numerically investigated. Generally the proton beam charge is determined by the areal density σ = nl of the second layer, while the accelerating field is governed by the substrate thickness L. From a series of onedimensional particle-in-cell simulations over a broad range of σ and L, it was confirmed that those two control parameters do not interfere significantly, indicating the beam charge and energy can be separately controlled. We suggest self-assembly monolayers technique be used for the fabrication of the areal density of the second layer.

Controlling the spectrum of high-power terahertz radiation from a laser-driven plasma wave

장도근,김진주,남인혁,허민섭,석희용 한국물리학회 2012 Current Applied Physics Vol.12 No.5

Generation of strong THz waves is a very important and difficult research issue. We performed particlein-cell (PIC) simulation studies to investigate the possibility of powerful THz generation and spectrum controllability by using a laser-driven plasma wave. Our results show that it is possible to produce spectrum-controllable high-power (>1 MV/cm) THz waves by manipulating the plasma density profiles. This method may provide a good way for coherent high-power THz radiation sources, of which the spectrum ranges from a narrow bandwidth to a wide bandwidth. Generation of strong THz waves is a very important and difficult research issue. We performed particlein-cell (PIC) simulation studies to investigate the possibility of powerful THz generation and spectrum controllability by using a laser-driven plasma wave. Our results show that it is possible to produce spectrum-controllable high-power (>1 MV/cm) THz waves by manipulating the plasma density profiles. This method may provide a good way for coherent high-power THz radiation sources, of which the spectrum ranges from a narrow bandwidth to a wide bandwidth.

Enhanced betatron radiation by a modulating laser pulse in laser wakefield acceleration

이승우,엄한섭,강태연,허민섭,석희용 한국물리학회 2019 Current Applied Physics Vol.19 No.4

We propose a new idea to enhance and control the betatron radiation by using a modulating laser pulse in laser wakefield acceleration. In this scheme, a high-power laser pulse is used for self-trapping and acceleration of the plasma electrons and the accelerated electron beam is modulated by a separately-propagating laser pulse for large amplitude betatron oscillations and microbunching. In this way, the relatively low power modulating laser pulse can enhance the X-ray photon flux and energy significantly. We performed two-dimensional particle-in-cell simulations to demonstrate the idea and the results show that a sub-TW laser pulse is enough for electron beam modulation and it can generate easily-controllable fs X-ray pulses with a wide range of photon energies from soft X-rays to hard X-rays.

Plasma Channel Generation for Electron Acceleration with a Laser-Induced Density Gradient

Hyojae Jang,석희용,Jaehoon Kim,허민섭,조무현,유승훈,남궁원 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I

Injection is a critical issue for the generation of a small-energy-spread, high-energy electron beam by using a laser wakefield accelerator (LWFA). By using a steep downward density gradient of plasma electrons at a gas target, a portion of the background electrons can be trapped locally in the laser wakefield, and they are accelerated by the field. To make a steep downward electron density gradient, we generated a pre-plasma using a 200-ps 800-mJ Nd:Glass laser, and we measured its electron density by using a Mach-Zehnder interferometer. Due to the shock structure of the plasma with a background neutral gas, a steep density gradient ($\sim 8\times10^{18}$ cm$^{-3}$/20 $\mu$m) could be generated. In the near future, a 20-TW, 30-fs Ti:Sapphire laser will be sent to this pre-plasma to generate an electron beam. In this paper, some preliminary experimental results and an ongoing work are reported.