High-resolution atomic-beam diode-laser spectroscopy in Sm I has been performed. Zeeman spectra have been measured for the three optical transitions at different external magnetic fields and well resolved at the magnetic fields of stronger than 6.0？mT. Using the known precise Landé -factors of the ground multiplet, the Landé -factors of the upper 4f66s6p？？ and levels have been determined, and their precision has been improved compared with the reference values. 1. Introduction Studies of the interaction of atoms with an external magnetic field, the Zeeman effect, have a long history and have been of repeated interests to spectroscopists [1–5]. The atomic Landé -factor, a measure of the atomic magnetic moment, can be deduced from the Zeeman spectroscopy and provides a sensitive test of atomic calculation [6–8]. The Zeeman effect is also related to the research of the atomic parity nonconservation [9]. Moreover, precise information of magnetic fields for interstellar clouds, which is important for understanding the role played by magnetic fields in star formation, can be obtained from the Zeeman observation [10–12]. Study of the Zeeman effect is, therefore, of much interest not only from the point of view of atomic physics but also from the point of view of other fields such as astrophysics. Samarium, a typical rare earth element, is suitable for measurements of the Zeeman effect because it has rich optical transitions and many stable isotopes. The Landé- factors of the 7F ground multiplet were precisely determined using an atomic-beam magnetic resonance [13, 14]. Some high-lying levels were measured by means of atomic-beam laser spectroscopy [15–17]. Martin et al. [18] tabulated Landé- factors for almost all known excited levels of Sm, and errors were not given. In this paper, we report high-resolution atomic-beam diode-laser spectroscopy in Sm I around 680？nm. Zeeman spectra at different external magnetic fields are measured and analyzed for three transitions. Using the known precise values of the Landé -factor of the ground multiplet, the Landé -factors of the upper levels are obtained, and results are discussed. 2. Experiment The present experiment was performed using a diode-laser beam and an atomic beam. The experimental setup is shown in Figure 1 and is essentially identical to that used in our previous works [19, 20]. Evaporation of Sm atoms was made using a resistance heating of a molybdenum oven. The oven temperature was controlled at about 900°C in order to produce a sufficient vapor pressure for Sm. An atomic beam was formed by a 2？mm diameter
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