Note: A helical velocity selector for continuous molecular beams

We report on a modern realization of the classic helical velocity selector for gas phase particle beams. The device operates stably under high vacuum conditions at rotational frequencies limited only by commercial dc motor capabilities. Tuning the rotational frequency allows selective scanning over a broad velocity band. The width of the selected velocity distributions at full-width-half-maximum is as narrow as a few percent of the selected mean velocity and independent of the rotational speed of the selector. The selector generates low vibrational noise amplitudes comparable to mechanically damped state-of-the-art turbo-molecular pumps and is therefore compatible with vibration sensitive experiments like molecule interferometry.

Wave and particle in molecular interference lithography

The wave-particle duality of massive objects is a cornerstone of quantum physics and a key property of many modern tools such as electron microscopy, neutron diffraction or atom interferometry. Here we report on the first experimental demonstration of quantum interference lithography with complex molecules. Molecular matter-wave interference patterns are deposited onto a reconstructed Si(111) 7x7 surface and imaged using scanning tunneling microscopy. Thereby both the particle and the quantum wave character of the molecules can be visualized in one and the same image. This new approach to nanolithography therefore also represents a sensitive new detection scheme for quantum interference experiments.

Simulated Speed Distributions for Effusing Gases in the Transition Region

Monte Carlo techniques were used to evaluate the flow of molecules through an ideal orifice (effusion) as predicted by isotropy-failure theory. Binary collisions of molecules were treated using classical mechanics with random numbers used for molecular speeds, directions, and recoil angles. Isotropy-failure theory was applied to give the dependence on pressure of the gas. Isotropy-failure theory assumes that the probability of escape is increased by the absence of the container wall where the orifice is located. The simulation was performed for Ar at 1000 K for 10(7) collisions. The simulation provided the number of molecules and their speeds in the orifice direction as a function of the isotropy-failure parameter domega/2pi (related to the Knudsen number defined as the mean-free path divided by orifice diameter). As domega/2pi increased (Knudsen number decreased, pressure increased) the transmission probability of the orifice increased, and the average speed of molecules escaping along the orifice normal increased. The results are compared to experimental results for the orifice transmission probability and speed distribution.

Velocity-specific atomic-state selection in an atomic beam by continuous-wave optical pumping

We present experimental results demonstrating strong velocity-distribution modification in a specific atomic state using optical pumping between hyperfine split levels. These results show that the velocity of a specific state can be defined within 6%, corresponding to a local temperature of 1 K. The velocity-specific-state selection is accomplished by using a nearly effusive atomic beam of sodium and a single frequency-stabilized dye laser.