  We report coherent association of atoms into a single weakly bound NaCs
molecule in an optical tweezer through an optical Raman transition. The Raman
technique uses a deeply bound electronic excited intermediate state to achieve
a large transition dipole moment while reducing photon scattering. Starting
from two atoms in their relative motional ground state, we achieve an optical
transfer efficiency of 69%. The molecules have a binding energy of 770.2MHz at
8.83(2)G. This technique does not rely on Feshbach resonances or narrow
excited-state lines and may allow a wide range of molecular species to be
assembled atom-by-atom.
