Investigation on the characteristics of the 2TW level $Nd^{3+}$:glass laser facility (Sinmyung I) for laser-fusion research and x-ray generation, consisted of a four-pass preamplifier and a five-stage main amplifier, were performed in this study. $Nd^{3+}$ ion doped phosphate glasses was used as gain media for these amplifier.
To increase the input pulse energy into five-stage main amplifier, we constructed a four-pass preamplifier which has operational reliability for dumping out an amplified pulse and on hot spot which usually causes optical damages in a gain medium. Compensating the polarization distortion caused by thermal birefringence, we could obtain the gain up to $2.5Ⅹ10^5$, and much better temporal profile than the conventional ways. Without compensating the polarization distortion, we could not obtain a gain larger than $6Ⅹ10^3$ because of self-lasing or generating many spikes in the amplifier.
The five-stage main amplifier was constructed with the spatial frequency filters and the beam expander since the output power of the laser is mainly limited by small scale and whole beam self focusing. Also we designed the pulse forming network with considering of the life time of flashlamps. The five-stage amplifier system was operated at a short-pulse high-power regime. A short single pulse is selected from a mode-locked and Q-switched Nd:YLF laser by Pockels cell syncronized with the laser pulse. The gain of this amplifier was approximately 8000 at 45kJ pumping energy. Also the good beam profiles was obtained without any optical damage. For the short pulse of 40ps, we obtained the high power of 2TW(80J) from four-pass and five-stage amplifier, and for the long pulse of 500ps, we expect that the obtainable energy is 470J(0.94TW). Also we proposed and demonstrated the self-pumping amplifier in which the energy of a pulse train was used as pumping source of a gain medium and the one pulse in this pulse train was amplified in the gain medium. Master oscillator was Q-switched and mode-locked (MLQS) Nd:YLF laser. The pumping source of a gain medium was the second harmonic of the MLQS laser, and $Nd^{3+}$:ethylene glycol was used as a gain medium. We could obtain the gain of approximately 2 from our amplifier. Such a setup can be used as the post amplifier of our TW laser system.
