  Understanding ultracold collisions involving molecules is of fundamental
importance for current experiments, where inelastic collisions typically limit
the lifetime of molecular ensembles in optical traps. Here we present a broad
study of optically trapped ultracold RbCs molecules in collisions with one
another, in reactive collisions with Rb atoms, and in nonreactive collisions
with Cs atoms. For experiments with RbCs alone, we show that by modulating the
intensity of the optical trap, such that the molecules spend 75% of each
modulation cycle in the dark, we partially suppress collisional loss of the
molecules. This is evidence for optical excitation of molecule pairs mediated
via sticky collisions. We find that the suppression is less effective for
molecules not prepared in the spin-stretched hyperfine ground state. This may
be due either to longer lifetimes for complexes or to laser-free decay
pathways. For atom-molecule mixtures, RbCs+Rb and RbCs+Cs, we demonstrate that
the rate of collisional loss of molecules scales linearly with the density of
atoms. This indicates that, in both cases, the loss of molecules is
rate-limited by two-body atom-molecule processes. For both mixtures, we measure
loss rates that are below the thermally averaged universal limit.
