[en] Laser spectroscopy has been developed to investigate the temporal and spatial behaviours of hydrogen and impurity atoms in fusion plasma. Among various schemes, tunable lasers were developed. The importance of the development of tunable VUV laser sources is based on the fact that the resonance-wavelengths of such hight-elements as hydrogen, carbon and oxygen are all in this range of wavelength. The frequency conversion method of tunable dye laser light by the third harmonic generation or two-photon resonance four-wave-sum-mixing in gaseous media was adopted. The maximum output was about 30 W in Kr/Ar mixture. The velocity distribution function of metal atoms and light elements was measured shot-by-shot by varying the spectrally narrowed pulse laser source. A fast-frequency-scan dye laser with the duration of the laser emission of 5 microsecond has been constructed. The system was applied to the measurement of the velocity distribution function of iron atoms sputtered by iron beam. The result was satisfactory. The system was applied for the studies of particle behaviour in various plasma, such as in linear machines like RFC-XX-M at the Institute for Plasma Physics, Nagoya University. A marked decrease of neutral hydrogen at the center of plasma in RFC-XX-M was for the first time confirmed in linear machines. The capability of measuring the density and velocity distribution functions of species, in situ, is fully exploited. (Kato, T.)