  Supersonic beams are a prevalent source of cold molecules utilized in the
study of chemical reactions, atom interferometry, gas-surface interactions,
precision spectroscopy, molecular cooling and more. The triumph of this method
emanates from the high densities produced in relation to other methods, however
beam density remains fundamentally limited by interference with shock waves
reflected from collimating surfaces. Here we show experimentally that this
shock interaction can be reduced or even eliminated by cryo-cooling the
interacting surface. An increase in beam density of nearly an order of
magnitude was measured at the lowest surface temperature, with no further
fundamental limitation reached. Visualization of the shock waves by plasma
discharge and reproduction with direct simulation Monte Carlo calculations both
indicate that the suppression of the shock structure is partially caused by
lowering the momentum flux of reflected particles, and significantly enhanced
by the adsorption of particles to the surface. We observe that the scaling of
beam density with source pressure is recovered, paving the way to order of
magnitude brighter cold molecular beams.

Atomic Physics;Atomic and Molecular Clusters;Chemical Physics;Quantum Physics