남인혁 교수

Using x-ray diffraction at the Linac Coherent Light Source x-ray free-electron laser, we have determined simultaneously and self-consistently the phase transitions and equation of state (EOS) of the lightest transition metal, scandium, under shock compression. On compression scandium undergoes a structural phase transition between 32 and 35 GPa to the same bcc structure seen at high temperatures at ambient pressures, and then a further transition at 46 GPa to the incommensurate host-guest polymo

The gas and ice giants in our solar system can be seen as a natural laboratory for the physics of highly compressed matter at temperatures up to thousands of kelvins. In turn, our understanding of their structure and evolution depends critically on our ability to model such matter. One key aspect is the miscibility of the elements in their interiors. Here, we demonstrate the feasibility of X-ray Thomson scattering to quantify the degree of species separation in a 1:1 carbon-hydrogen mixture at a

Diamond formation in polystyrene (C8H8)n, which is laser-compressed and heated to conditions around 150 GPa and 5000 K, has recently been demonstrated in the laboratory [Kraus et al., Nat. Astron. 1, 606–611 (2017)]. Here, we show an extended analysis and comparison to first-principles simulations of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray sca

Based on two-dimensional particle-in-cell simulations, we investigated the electron beam’s transverse oscillations by temporally asymmetric laser pulses in laser wakefield acceleration. Of particular interest in this article are the effects of ultrashort laser pulses having sharp rising and slow falling time scales. In this situation, the accelerated electron beam interacts directly with the laser field and undergoes transverse oscillations due to a phase-slip with the laser field. This oscillat

Abstract This research reports the increased electron energy gain from laser wakefield acceleration in density-modulated plasma with an external magnetic field. Periodic plasma density- modulation can excite higher harmonics of different phase velocities of fundamental wakefield that can assist in improving the self-trapping of pre-accelerated electrons to accelerate them for higher energy. Furthermore, the applied magnetic field assisted self-injection can also contribute in electron energy enh

This paper studies zirconium subjected to high pressure conditions. Using x-ray diffraction, the authors observe the onset of melting at short times after shocking, and refreeze shortly thereafter. The latent heat of crystallization is found to provide the energy for the recrystallization process

The demonstration of a harmonic lasing self-seeded free-electron laser (HLSS FEL) scheme in the soft X-ray range at the Pohang Accelerator Laboratory X-ray Free Electron Laser is presented. We report the experimental results of HLSS FEL radiation with the shortest wavelength of 1 nm by using the optimized phase shift of 2/3π. The key feature of the HLSS scheme is that the mode number is decreased (the longitudinal coherence length is enhanced) which is directly observed using a single-shot spect

Generation of petawatt-class pulses with a nearly single-cycle duration or with a strongly asymmetric longitudinal profile using a thin plasma layer are investigated via particle-in-cell simulations and the analytical flying mirror model. It is shown that the transmitted pulses having a duration as short as about 4 fs (1.2 laser cycles) or one-cycle front (tail) asymmetric pulses with peak intensity of about 10^{21}W/cm^{2} can be produced by optimizing system parameters. Here, a new effect is f

We successfully demonstrated the generation of single-cycle terahertz (THz) pulses through tilted-pulse-front (TPF) pumping using a reflective echelon in a lithium niobate crystal. By optimizing the pump pulse duration using a chirp, we achieved a maximum pump-to-THz conversion efficiency of 0.39%. However, we observed that the saturation behavior began at a relatively low pump energy (0.37 mJ), corresponding to a pump intensity of 22 GW/cm 2 . To elucidate this behavior, we measured the near- a

The measurement of the plasma density is of crucial importance in laser-plasma accelerators. We measured the spatial and the temporal plasma/gas densities in a capillary gas-cell by using the interferometric and the Raman scattering methods. By using transverse interferometry, we were able to measure directly the spatial distribution of the electron density between the entrance and the location of gas injection in the capillary, and we compared the result with that from a computational fluid dyn

Abstract In the laser wakefield acceleration (LWFA), the dephasing problem is a serious energy-limiting factor, which is caused by the velocity difference between the accelerated electrons and the laser wake wave. To overcome the dephasing problem, we developed a special capillary gas-cell with a density up-ramp along the laser propagation direction and used it for electron acceleration experiments. Our experiments, which were performed with a peak laser power of 15 TW at GIST, show that the ele