Kitae Lee

HE11 mode in a waveguide THZ FEL

A new free electron laser (FEL) in the terahertz band is now being developed at the Korea Atomic Energy Research Institute under the state program World Class Institute. It is a compact machine driven by a microtron. The FEL itself is a cylindrical waveguide resonator mounted in a helical undulator. This scheme allows us to obtain a sizable amplification coefficient at a moderate beam current, but the attenuation of a wave in the waveguide is too high. It is proposed that the inner surface of the waveguide be coated with a dielectric film to reduce attenuation. The working mode is in this case not H11, as with a pure metal waveguide, but the hybrid HE11. Results from numerical simulations for this waveguide are presented. Various coating substances are considered. Conclusions are drawn as to the advisability of this method.

Development of advanced radiation sources at KAERI

The KAERI Center for Quantum Beam-Based Radiation Research, was founded in 2011. The center pursues the development of advanced radiation sources and their applications in biology, material science, and nuclear physics. There are two main research topics in the development of advanced radiation sources: a system with high-power T-ray pump and an ultrashort X-ray probe system and a compact electron storage ring based on a laser-accelerated electron beam.

Optical Parametric Chirped - pulse Amplification of Femtosecond Ti : sapphire Laser Pulses by Using a BBO Crystal

We have characterized the optical parametric chirped-pulse amplification of femtosecond Ti:sapphire laser pulses by using a BBO crystal. It is numerically verified that a high gain and a broad gain bandwidth can be obtained with a 532-nm pump laser. The dependence of the gain profile of OPA on phase matching angles, pump intensity, and crystal length is numerically investigated. Experimental results shows that the temporal fluctuation of a pump laser causes the modulation of an amplified spectrum in OPCPA.

Sequence effect of optical elements in a femtosecond Ti:sapphire laser oscillator

We have numerically and experimentally verified that the sequence of optical elements in a femtosecond Ti:sapphire laser affects the laser’s characteristics. Even with the same net dispersion in a cavity, the output spectrum showed a significant change in width and shape when the sequence of dispersive elements was changed in a Kerr-lens mode-locked Ti:sapphire laser with fused-silica prisms for dispersion compensation. It was also shown that the output coupler’s position can affect the dynamics of pulse formation by the combined action of output coupling and self-phase modulation. We explain such phenomena based on pulse formation in a laser cavity with discrete distribution of dispersion and self-phase modulation.

Generation of laser-induced fast neutrons and application for activation analysis

A laser-induced repetitively operated fast neutron source was developed by using a deuterated polystyrene film target and a femtosecond laser with a peak output power of approximately 24 TW and was applied for laser activation analyses of indium and gold samples. By using a home-made gated scintillation detector, the developed neutron source was estimated to have a neutron yield of approximately 4 × 105 n/pulse at a pulse repetition rate of 5 Hz. For the neutron yield, relatively strong delayed gamma spectra were measured at 138 keV, 417 keV, 1097 keV, and 1294 keV for the activated indium, and at 333 keV and 355 keV for the activated gold. In addition to the delayed spectra, several prompt gamma spectra were measured during gold activation. These suggest possible uses of the neutron source for activation analysis of various materials.

Prospects and progress of the 1 kJ Nd: Glass laser Facility at KAERI

The Korea Atomic Energy Research Institute (KAERI) began to construct the 1 kJ Nd:glass laser facility. The KAERI laser facility (KLF) is designed to deliver 1 kJ at n-sec and 50 TW at p-sec to target chamber for high energy density plasma physics.

Characterization of OPCPA with BBO crystal for femtosecond Ti:sapphire laser pulses

We have numerically and experimentally investigated the characteristics of the optical parametric chirped-pulse amplification (OPCPA) of femtosecond Ti:sapphire laser pulses by using BBO crystals. Numerical calculations showed that a high gain and a broad gain bandwidth could be obtained with a 532-nm pump laser. The dependence of the gain profile of OPA on phase matching angles, pump intensity, and crystal length was numerically investigated. Experimental results showed that the broadband amplification of femtosecond Ti:sapphire laser pulses could be realized by OPCPA and that the temporal fluctuation of a pump laser resulted in the modulation of amplified spectra in OPCPA.

3D Monte-Carlo Simulation of Zeeman Slower System with Two Level Atoms

We report three dimensional numerical simulations of a Zeeman slower system with two level atoms. We choose the magnetic field intensity distribution from experimental data and atomic conditions from population analysis of the transitions between F=2 and F=3 lines of the Na atom. We use the Monte-Carlo method for simulation. We generate three kinds of random numbers to specify the initial velocity of the atoms and one more random number for the event of the spontaneous emission. We treat the stimulated emission with numerical solution of the Bloch equation for two level atoms. We put atoms into the Zeeman slower system one by one and follow the motion of each atom. Two forces are considered; one is the intensity gradient force caused by stimulated emission and the other is the divergence force caused by spontaneous emission. We employ a parameter related with the atomic states at the exit port of the Zeeman slower. This parameter is related with space distribution and the velocity distribution of the atom at the exit. We analyze threekinds of the laser beam conditions; one is the focusing condition, another being intensity conditions and the last one being intensity shape conditions of the laser beam front.