Schematic of the surface electrostatic velocity filter
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Figure 1. Schematic of the surface electrostatic velocity filter. An effusive beam is produced by expansion of a low source pressure gas of polar molecules through a pulsed valve, and then enters into the surface electrostatic velocity filter. Only molecules below a certain threshold velocity can be guided by the filter, while faster ones rush out of the guiding tube. The inset illustrates the two-dimensional (2D) cut through the bend filter in a plane perpendicular to both the electric plates and the substrate, together with contours of a tubular electrostatic field above the surface of the electrode (in units of V/m).
We propose a scheme of a surface electrostatic velocity filter capable of preparing cold polar molecules on the surface of a substrate by selecting a low-velocity component of an effusive beam from a thermal gas reservoir. Using ND3 as a molecular sample, the dependence of the performance of the filter on the parameters of both the filter setup and the incident molecular beam is investigated by using a theoretical model and Monte Carlo simulations. A detailed study of the guiding process of molecules, including the evolution of phase space density of the packet in the filter, is carried out and shows that the beam selection process is mainly completed in the front part of the filter.