Slow ammonia molecules in an electrostatic quadrupole guide

An electrostatic quadrupole is used to filter slow dipolar ND3 molecules from an effusive source and to guide them into ultrahigh vacuum. The molecules in the electrostatic quadrupole experience a Stark interaction which allows filtering of small velocities in the linear and bent sections of the quadrupole. With this technique we demonstrate a flux of \(\approx 10^{10}\)/s with a longitudinal temperature of a few K. The technique and the set-up are discussed in detail, and the guided gas as well as the output beam are characterized. Improvements in the set-up are highlighted, as for instance cooling of the effusive source to below 150 K.