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We have measured the deflection of a thermal sodium beam by a force existing in a field of two counterpropagating short laser pulses. This field was created by a Π-pulse train of a mode-locked (mode) (spacing 82 MHz) dye laser beam, perpendicularly crossing a thermal sodium beam and retroreflected from a mirror behind it. Unlike the spontaneous force, this Π-pulse force is not limited by saturation effects and does not heat up the sodium beam transversally. Calculations yield a maximum Π-pulse force about three times larger than the spontaneous force, being in good agreement with our experimental results.( * ) This work is part of the thesis of B. Nölle.

Abstract. Cooling and optical pumping by a circularly polarized two mode laser is applied to a Na atomic beam in transverse geometry. The low velocity components of the beam are transversly cooled to the Doppler limit temperature of 240 btK and are simultaneously spin polarized for more than 90%. PACS: 32.80.P Scattering experiments with subthermal spin polarized atoms in the ground state open a new field of interesting physics [ 1]. From the measured total cross section the long range interatomic potential can be determined. Measuring the differential cross section offers the possibility to investigate hyperfine decoupling processes during the scattering with collision energies about equal to the Na ground state hyperfine splitting (1772 MHz).For information about the scattered particles being distinguishable or undistinguishable we have to manipulate the atomic spin polarization.We have set up an experiment to cool and polarize a Na atomic beam in transverse geometry, i.e., two counterpropagating laser beams of the same circular polarizations illuminate the Na beam at right angle [2] (Fig.