Radiative deflection of a BaF molecular beam from the optical cycling

We demonstrate a quasi optical cycling for the $X(v=0)\to A(v'=0)$ transition and a radiative force induced deflection on the buffer-gas cooled BaF molecular beam. The laser induced fluorescence enhancement with additional sidebands and a polarization modulation scheme indicates that the hyperfine states and the Zeeman sublevels are closed. The quasi optical cycling by repumping the $X(v=1)\to A(v'=0)$ leads to a $\sim$ 0.8 mm deflection of the beam via scattering $\sim$ 150 photons per molecule, in good agreement with the predictions from our multi-level rate equation model. Further improvement by closing the leakage $X(v=2)$ and $\Delta$ state allows scattering thousands of photons, and laser cooling and slowing of BaF.