Biomedical subjects

Hendrick L Bethlem

Publications and source records attributed to Hendrick L Bethlem.

5 recordsLinked to original sources

PubMed2006

Molecular beams with a tunable velocity.

The merging of molecular beam methods with those of accelerator physics has yielded new tools to manipulate the motion of molecules. Over the last few years, decelerators, lenses, bunchers, traps, and storage rings for neutral molecules have been demonstrated. Molecular beams with a tunable velocity and with a tunable width of the velocity distribution can now be produced, and are expected to become a valuable tool in a variety of physical chemistry and chemical physics experiments. Here we present a compact molecular beam machine, capable of producing 3D spatially focused packets of state-selected accelerated or decelerated molecules.

Chemistry, Physical↗

PubMed2005

ac electric trap for ground-state molecules.

We here report on the realization of an electrodynamic trap, capable of trapping neutral atoms and molecules in both low-field and high-field seeking states. Confinement in three dimensions is achieved by switching between two electric field configurations that have a saddle point at the center of the trap, i.e., by alternating a focusing and a defocusing force in each direction. The ac trapping of 15ND(3) molecules is experimentally demonstrated, and the stability of the trap is studied as a function of the switching frequency. A 1 mK sample of 15ND(3) molecules in the high-field seeking component of the |J,K=|1,1 level, the ground state of para-ammonia, is trapped in a volume of about 1 mm(3).

Journal Article↗

PubMed2004

Microstructured switchable mirror for polar molecules.

By miniaturizing electrode geometries high electric fields can be produced using modest voltages. A planar array of 20 microm wide gold electrodes, spaced 20 microm apart, is made on a sapphire substrate. A voltage difference of up to 350 V is applied to adjacent electrodes, generating an electric field that decreases exponentially with distance from the substrate. This microstructured array can be used as a mirror for polar molecules and can be rapidly switched on and off. This is demonstrated by retro-reflecting a beam of state-selected ammonia molecules with a forward velocity of about 30 m/s.

Journal Article↗

PubMed2002

Longitudinal focusing and cooling of a molecular beam.

A neutral polar molecule experiences a force in an inhomogeneous electric field. This electric field can be designed such that a beam of polar molecules is exposed to a harmonic potential in the forward direction. In this potential the longitudinal phase-space distribution of the ensemble of molecules is rotated uniformly. This property is used to longitudinally focus a pulsed beam of ammonia molecules and to produce a beam with a longitudinal velocity spread of 0.76 m/s, corresponding to a temperature of 250 mu K.

Journal Article↗

PubMed2002

Alternate gradient focusing and deceleration of a molecular beam.

Neutral dipolar molecules can be decelerated and trapped using time-varying inhomogeneous electric fields. This has been demonstrated only for molecules in low-field seeking states, but can, in principle, be performed on molecules in high-field seeking states as well. Transverse stability is then much more difficult to obtain, however, since molecules in high-field seeking states always experience a force towards the electrodes. Here we demonstrate that an array of dipole lenses in alternate gradient configuration can be used to maintain transverse stability. A pulsed beam of metastable CO in high-field seeking states is accelerated from 275 to 289 m/s as well as decelerated from 275 to 260 m/s.

Journal Article↗