[en] In this study, Ti:sapphire laser which is pumped by the enhanced Nd:YAG laser using laser diode, was designed and manufactured. The AO Q-switched CW Nd:YAG laser was converted into a high repetition plus-type laser using the AO Q-switch, and two heads were installed inside the cavity in order to improve the laser beam quality. The Nd:YAG laser enhancement was completed by optimization using a simulation for the cavity length, structure and thermal lens effect that greatly effected the laser beam output and quality. As the result of the enhancement, a 30W laser at 532nm and at 5k-Hz was successfully made. Also, the Ti:sapphire laser that will be used for atomic spectroscopy which is pumped by the Nd:YAG laser, was completely designed. As a basic experiment for laser oscillation. We measured the tunability of the laser, and it turned out that the wave tunability range was 730 850 nm. A self-seeding type tunable laser using grating for narrow line width, is planned to be designed due to the fact that the Ti:sapphire laser should be of narrow line width for spectroscopy use

[en] This research completed the manufacturing of the Ti:sapphire laser pumped by a DPSSL that was improved this year. A 1800 gr/mm grating was used to reduce the line width of the laser oscillator which has a wide wavelength over 100 nm, and a tuning mirror was used to tune the wavelength of the laser oscillator to the resonant wavelength of the atomic transition line that was to be ionized. The wavelength range of the Ti:sapphire laser was 730 nm - 850 nm, and output power of approximately 1.1 W (approx. 1.1mJ of energy per pulse) was obtained in the case when pumped by 9.0 W of DPSSL using the self-seeding type. UV oscillation was achieved by second harmonic generation of the Ti:sapphire laser. The wavelength range of UV laser was 380 nm - 420 nm, and the output energy per pulse was approximately 150 uJ when the Ti:sapphire laser was pumped by 1.0 W. In order to detect the Yb photo-ion that was ionized by the UV laser, a mass analyzer that used to be used in the laboratory was partially improved. As a result of the experiment, the resonant ion signal was observed in the 398.8nm wavelength, and it could be concluded that the observed ion signal strength was not smaller than that of the resonance ionization in the visible range

[en] At the Korea Atomic Energy Research Institute (KAERI), a 30-TW Ti:Sapphire laser system with an energy of 1 J and a pulse width of 30 fs has been developed. Currently, we are conducting various research projects, such as Compton back-scattering X-rays, relativistic nonlinear Thomson scattering, and the generation of high-energy ions, terahertz (THz) pulses, and fusion neutrons, for medical and nuclear research with a laboratory-scale system. This paper will briefly review the status of the KAERI activity on the generation of ultra-fast, high-energy particles and the prospects for nuclear applications.

[en] The development of a CPA (Chirp-Pulse-Amplification) laser technology has opened a new regime in physics, relativistic plasma. The relativistic plasma is much interesting not only by its fundamental aspects but also its copious applications such as acceleration of charged particles, generation of ultrashort radiation pulses. Those fields are very attractive due to its compactness compared with conventional technology. KAERI is performing researches on the relativistic plasma physics and its applications, in which high energy proton generation for the medical application and atto-second radiation pulse are included. Experimental facilities under development for the generation of proton beams and numerical simulation results for the generation of atto-second pulse through nonlinear Thomson scattering will be presented

[en] International treaties on the reduction of green-house gases are now being established worldwide and Korea is supposed to join these treaties in a near future. Meanwhile the energy production via fission reactors proposed as a solution to this global environmental contamination has still inherent problems in that it also produces long-life radioactive nuclear waste in the long run, causing many serious social issues. Now the ultimate solution in this situation is believed to be the production of energy by the nuclear fusion reaction. In this project, the collaboration regarding high energy laser fusion has been carried out mainly at the Chinese facility such as ShengGuang II (SG II) laser facility, and ultrahigh intensity laser system of KAERI has been used for the small scale laser fusion and production of fast neutrons. Thomson scattering experiment to analyze the fusion plasma, opacity measurement to understand and develop the computer simulation techniques have been carried out at SG II facility, and experiments on implosion reaction which is basic to laser fusion as well as that of X-ray absorption and transmission have been done at the GEKKO XII facility of ILE, Japan. Satisfactory results both for Korea and China have been deduced by the strategy of project such that different approaches for high energy laser fusion and low energy laser fusion were applied. That is, Korean partner could get opportunities of doing experiments at the large laser facilities to get plasma diagnostic technologies and high density simulation technologies, besides the opportunity to participate in the K-C-J collaborative experiments of implosion and X-ray spectroscopy. And Chinese partner could solve their problem related to the laser fusion and neutron generation which were not successful even with their far high 300TW laser system

[en] We report the dielectric functions of InP at temperatures between 25 K and 700 K measured by using spectroscopic ellipsometry (SE) in the energy range from 1.19 to 6.57 eV. A blue shift and a separation of critical point (CP) structures were observed at low temperatures, which is explained by the reduced electron-phonon interaction and by the thermal expansion. The values of the CP energies were determined from numerically-calculated second energy derivatives of the data. Separation of the E₂ CP structures (4 - 6.5 eV), which could not be detected at room temperature, was clearly shown at low temperatures. We report the temperature dependences of the E'₂ and the E'₁ CP energies, which have not been observed so far by using SE.

[en] Neutron generation through Coulomb explosion of deuterium contained gas clusters is known as one of the very effective methods to produce fusion neutrons using a table top terawatt laser. The energy of ions produced through Coulomb explosions is very important factor to generate neutrons efficiently. Until the ion energy reaches around∼MeV level, the D D fusion reaction probability increases exponentially. The understanding of laser beam propagation and laser energy deposition in clusters is very important to improve neutron yields. As the laser beam propagates through clusters medium, laser energy is absorbed in clusters by ionization of molecules consisting clusters. When the backing pressure of gas increases, the average size of clusters increases and which results in higher energy absorption and earlier termination of laser propagation. We first installed a Michelson interferometer to view laser beam traces in a cluster plume and to measure spatial electron density profiles of a plasma channel which was produced by a laser beam. And then we measured the energy of ions distributed along the plasma channel with a translating slit to select ions from narrow parts of a plasma channel. In our experiments, methane gas was used to produce gas clusters at a room temperature and the energy distribution of proton ions for different gas backing pressure were measured by the time of flight method using dual micro channel plates. By comparing the distribution of ion energies and electron densities, we could understand the condition for effective laser energy delivery to clusters

[en] We have experimentally investigated the interaction of intense, femtosecond laser pulse with a cryogenically cooled Ar gas jet via tim-integrated soft X-ray spectroscopy. New spectral lines from Ar⁸⁺, Ar⁹⁺ and Ar¹⁰⁺ charge states appeared with decreasing pre-expansion gas temperature. The drastic change in the spectrum was attributed to collisional heating and collisional ionization of Ar clusters which were formed in the cooled jet. (author)

[en] At Korea Atomic Energy Research Institute (KAERI), a 30-TW Ti:Sapphire laser system with energy of 1 J and pulse width of 30 fs, has been developed. Currently we are conducting various researches such as Compton back-scattering x-ray, relativistic nonlinear Thomson scattering, and generation of high energy ions, terahertz (THz) pulses and fusion neutrons for the study of medical and nuclear researches with laboratory-scale system. This paper will briefly review the status of the KAERI activity on the generation of the ultra-fast, high-energy particles for the prospects of nuclear applications. (author)

[en] Energetic ion beams generated from thin foil targets by irradiating an ultra intense laser pulse have attracted much attention due to its fundamental aspects and potential applications. Even though there was a long standing controversy on the origin of the proton beams, recently it has been found that the isothermal expansion of the target normal sheath acceleration (TNSA)model is a dominant acceleration mechanism in the case of metal targets. However there are observations that more intense proton beams with higher energies are generated from the plastic target, which could not be explained with the TNSA model. The maximum proton energies obtained by irradiating a 30 fs Ti:Sapphire laser pulse with an intensity of 2.2x10"1"8W/cm"2 on aluminum and Mylar targets for various thickness, are plotted in Fig. 1. This clearly shows that there is a distinct difference between metal and plastic targets in the maximum proton energies on the laser intensity lower than 10"1"9W/cm"2. We developed an acceleration model, acceleration by a resistively induced electric field (ARIE), in which the proton beams are accelerated from the front side of the target by the resistively induced electric field based on the analysis of Bell et al. With a reasonable assumption of plasma resistivities of 10∼100μΩm, it can reproduce the experimental observations for the case of the plastic targets. In the case of the plastic target, even though the maximum proton energy also increases as τ"ASE"decreases, there is no difference on the target thickness. In the ARIE model, since the protons are accelerated from the front side of the target, target thickness does not matter. Thus these results can also be considered to support the ARIE model