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We have been developing the TEA CO2 laser/D2O laser system and the detection system for the ion Thomson scattering experiment on the Heliotron E device in Kyoto University. Up to now a considerable effort has been concentrated on the improvement of the laser output characteristics such as (i) output energy, (ii) pulse duration and (iii) spectral purity. Recently, we have succeeded in obtaining high power, single mode TEA CO2 laser beams with good reproducibility, by developing a relatively compact TEA CO2 laser system. It consists of a main laser oscillator (Lumonics 601) and a triple-pass amplifier (Lumonics 620). The main laser (601) is injection-locked by the output pulse from a hybrid laser consisting of a cw CO2 laser section and a TEA CO2 laser section (Lumonics K921S). The cavity length of the main laser (601) is feedback controlled by making use of the cw CO2 laser signal, so that the single mode output is obtained with high probability. The output pulse duration of the main laser is also maximized by properly choosing the injection time after the initiation of the main discharge. The typical pulsewidth of the main laser in the case of the pulsed injection locking, is about 0.6 μs and the output energy is about 4 J at the line of 9R22. Then the laser beam is amplified by a triple pass amplifier up to 100 J . The burn patterns of the amplifier output beams show roughly uniform intensity distribution at the input window of the D2O laser. The 4 m long, unstable D2O laser consists of a set of concave and convex mirrors and a wire grid. We measured the output power of the D2O laser with a Scientech power meter and the maximum power of 200 mJ was obtained at a pressure of about 5 Torr. The measurements of the D2O laser emission linewidth were already carried out by the MIT 1) and Lausanne groups 2). However, the detailed spectral structures of the D2O laser were not obtained yet, because the frequency resolutions were limited to the bandwidth of filter used in their detection systems, say, 80 MHz, which are broader than the longitudinal mode spacings.
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