Continuous source of translationally cold dipolar molecules

The Stark interaction of polar molecules with an inhomogeneous electric field is exploited to select slow molecules from a room-temperature reservoir and guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole with a curved section selects molecules with small transverse and longitudinal velocities. The source is tested with formaldehyde $\left({\mathrm{H}}_2\mathrm{CO}\right)$ and deuterated ammonia $\left({\mathrm{ND}}_3\right).\mathrm{}$ With ${\mathrm{H}}_2\mathrm{CO}$ a continuous flux is measured of $\approx {10}^9/\mathrm{s}$ and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.