Creation of 'Alkali-Helium' miticisle and clusters, and laser spectroscopy

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The dynamics of atomic state, which is perturbed incoherently by thermal motion of surrounding particles, can be optically observed at low temperature. The information of atomic coherence is helpful to study basic concepts of quantum mechanics.Thulium atom in liquid and solid helium is studied by observing the optical transition between inner electronic shells. The metastable state is detected by trapping thulium atoms with high density in solid helium. This result makes atom in solid helium applicable to accurate measurement of atomic constants. We can also trap atoms with the technique of laser cooling. Because of high density of cooled atom, the energy or phase of optical transition is affected by the inter-atomic interactions which should be studied for accurate atomic clock. We treat O^-_ in alkali halide crystals as high density molecules, and observe the emission with high temporal and spectral resolution. Remarkable phenomena is superfluorescence from the high density O^-_ thin layr.The optical detection of atoms and molecules at low temperature is easy to change their electronic state and structure, because the energy of light is much larger than that of interaction with the surrounding atoms. In order to observe the atomic state non-destructively, we use RF field addition to laser light. High resolution magnetic resonance enable us to distinguish the kind of atoms and clusters. Three-dimensional magnetic resonance imaging(MRI)informs us the distribution of atoms at low temperature.At present we can observe the magnetic resonance and two-dimensional MRI of Cs in helium gas. Image is sensitively observed by optical pumping and detection. From the delay time from pumping to detection, we can look at diffusion of polarized Cs. In future we will measure the diffusion constants over wide temperature range, and MRI of rare gas atoms at low temperature.