Stark deceleration allows for precise control over the velocity of a pulsed molecular beam and, by the nature of its limited phase-space acceptance, reduces the energy width of the decelerated packet. We describe an alternate method of operating a Stark decelerator that further reduces the energy spread over the standard method of operation. In this alternate mode of operation, we aggressively decelerate the molecular packet using a high phase angle. This technique brings the molecular packet to the desired velocity before it reaches the end of the decelerator; the remaining stages are then used to longitudinally and transversely guide the packet to the detection/interaction region. The result of the initial aggressive slowing is a reduction in the phase-space acceptance of the decelerator and thus a narrowing of the velocity spread of the molecular packet. In addition to the narrower energy spread, this method also results in a velocity spread that is nearly independent of the final velocity. Using the alternate deceleration technique, the energy resolution of molecular collision measurements can be improved considerably.
Stark deceleration allows for precise control over the velocity of a pulsed molecular beam and, by the nature of its limited phase-space acceptance, reduces the energy width of the decelerated packet. We describe an alternate method of operating a Stark decelerator that further reduces the energy spread over the standard method of operation. In this alternate mode of operation, we aggressively decelerate the molecular packet using a high phase angle. This technique brings the molecular packet to the desired velocity before it reaches the end of the decelerator; the remaining stages are then used to longitudinally and transversely guide the packet to the detection/interaction region. The result of the initial aggressive slowing is a reduction in the phase-space acceptance of the decelerator and thus a narrowing of the velocity spread of the molecular packet. In addition to the narrower energy spread, this method also results in a velocity spread that is nearly independent of the final velocity. Using the alternate deceleration technique, the energy resolution of molecular collision measurements can be improved considerably.
With the Stark deceleration technique, packets of molecules with a tunable velocity, a narrow velocity spread, and a high state purity can be produced. These tamed molecular beams find applications in high resolution spectroscopy, cold molecule trapping, and controlled scattering experiments. The quality and purity of the packets of molecules emerging from the decelerator critically depend on the specifications of the decelerator, but also on the characteristics of the molecular beam pulse with which the decelerator is loaded. We consider three frequently used molecular beam sources, and discuss their suitability for molecular beam deceleration experiments, in particular with the application in crossed beam scattering in mind. The performance of two valves in particular, the Nijmegen Pulsed Valve and the Jordan Valve, is illustrated by decelerating ND 3 molecules in a 2.6 meter-long Stark decelerator. We describe a protocol to characterize the valve, and to optimally load the pulse of molecules into the decelerator. We characterize the valves regarding opening time duration, optimal valve-to-skimmer distance, mean velocity, velocity spread, state purity, and relative intensity.
Improving the number and number density of cold molecules is a longstanding goal in cold molecule research. Stark deceleration provides an important access to taming polar molecules and makes the collision and high-resolution spectroscopy a reality. However, the full deceleration efficiency of the traditional Stark decelerator has been impeded by its intrinsic loss mechanisms, which significantly limit its applications. In this paper, we introduce an interspersed guiding deceleration strategy that surpasses the periodic phase stability limitations of traditional Stark decelerator. Our approach is theoretically and experimentally validated using the ND3 molecule, achieving significant gains of $3\ensuremath{\sim}8$ for all final velocity ranges. Additionally, our method requires a lower operation number of switching that is beneficial for reducing the consumption of the high-voltage switches and suitable for controlling a large number of deceleration stages. This method is applicable to any traditional crossed-pin Stark decelerator and can stop a wider variety of molecular species with higher densities, including those with a small Stark shift-to-mass ratio. It is anticipated to become an essential tool for producing cold and dense molecular samples, offering promising prospects for cold collision studies and precision measurements.
We experimentally test our homemade electrostatic Stark decelerator with 99 slowing stages with a supersonic ND 3 molecular beam. Relationships between the performance of the decelerator and various parameters, including the kinetic energy loss per stage versus the synchronous phase angle ϕ 0 , the final central velocity of a slowed molecular packet versus both the phase angle ϕ 0 and the decelerating stage number and the relative slowing efficiency versus the phase angle ϕ 0 , are studied both theoretically and experimentally. With our homemade Stark decelerator, a supersonic ND 3 beam is successfully decelerated from 330 to 24 m s −1 , producing a molecular packet with a translational temperature of ∼36 mK. Experimental results are in good agreement with their simulated and theoretically calculated counterparts. In addition, we propose and study a new mode to operate a Stark decelerator that allows one to prepare a slow, number-density-enhanced, high-energy-resolution molecular beam, which is essentially a complementary mode to the scheme proposed by Parazzoli et al (2009 New J. Phys. 11 055031) in a low velocity regime and promises important applications in the research of cold collisions and cold chemistry.
Cryogenic buffer-gas beams are a promising method for producing bright sources of cold molecular radicals for cold-collision and chemical-reaction experiments. In order to use these beams in studies of reactions with controlled collision energies or in trapping experiments, one needs a method of controlling the forward velocity of the beam. A Stark decelerator can be an effective tool for controlling the mean speed of molecules produced by supersonic jets, but efficient deceleration of buffer-gas beams presents new challenges due to longer pulse lengths. Traveling-wave decelerators are uniquely suited to meet these challenges because of their ability to confine molecules in three dimensions during deceleration and their versatility afforded by the analog control of the electrodes. We have created ground-state $\mathrm{CH}(X{\phantom{\rule{0.16em}{0ex}}}^{2}\ensuremath{\Pi})$ radicals in a cryogenic buffer-gas cell with the potential to produce a cold molecular beam of 1011 molecules/pulse. We present a general protocol for Stark deceleration of beams with a large position and velocity spread for use with a traveling-wave decelerator. Our method involves confining molecules transversely with a hexapole for an optimized distance before deceleration. This rotates the phase-space distribution of the molecular packet so that the packet is matched to the time-varying phase-space acceptance of the decelerator. We demonstrate with simulations and an analytic one-dimensional model that this method can decelerate a significant fraction of the molecules in successive wells of a traveling-wave decelerator to produce energy-tuned beams for cold and controlled-molecule experiments.
In this paper, we investigate theoretically the Stark deceleration and cooling of subsonic NH3 molecular beams based on our second-generation electrostatic Stark decelerator with 180 stages. Firstly, we calculate the Stark shifts of NH3 molecules in the |J=1, K=1 ightangle states and show the stable area of longitudinal phase space for different synchronous phase angles. Secondly, we study the slowing performance of NH3 molecular beams in the traditional mode, and discuss the relationships between various parameters (such as the kinetic energy loss per stage, final velocity and the slowing efficiency) and the synchronous phase angle 0, as well as the dependence of final velocity on the applied voltages. It is found that a subsonic NH3 molecular beam can be decelerated from 280 to 6.7 m/s at 0=26.08 when the high voltages applied on the electrodes are 13 kV, corresponding to a removal of 99.9% kinetic energy. The translational temperature of the molecular packets in the moving frame is significantly reduced from 1.34 K to 80 mK. Finally, we study the slowing performance of NH3 molecules and the dependence of final velocity on the synchronous phase angle in an alternate operation mode. In this mode, a synchronous phase angle 0=0 is chosen to bunch the molecules by using the first 15 stages. The remaining 165 stages are then used to slow a subsonic molecular beam at a certain synchronous phase angle. Our result shows that a molecular beam with a mean velocity of 280 m/s can be decelerated to 20.7 m/s at 0=65.4 when the voltages applied are 6.5 kV, indicating a 99.4% kinetic energy removal, and the translational temperature of the molecular packets can be reduced from 1.34 K to 1.6 mK. By comparing the results obtained from the two operational modes, the temperature of the slowed molecular packet in the alternate mode is 50 times lower than that in the traditional mode. It is shown that our second-generation 180-stage Stark decelerator can effectively produce slow and cold molecules with relatively small electric dipole moment like NH3. These monochromatic NH3 molecular beams offer a promising starting point for high resolution spectroscopy, precision measurement, cold collisions and cold chemistry. This theoretical work provides a reliable basis in our further experimental research.
Abstract We demonstrate the production of cold, slow NH3 molecules from a supersonic NH3 molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supersonic NH3 molecular beam can be easily decelerated to trappable velocities. Here we present two modes for operating the Stark decelerator to slow the supersonic NH3 molecules. The first is the normal mode, where all 179 stages are used to decelerate molecules, and it allows decelerating the NH3 molecular beam from 333 m/s to 18 m/s, with a final temperature of 29.2 mK. The second is the deceleration-bunch mode, which allows us to decelerate the supersonic NH3 beam from 333 m/s to 24 m/s, with a final temperature of 2.9 mK. It is clear that the second mode promises to produce colder (high-energy-resolution) molecular samples than the normal mode. Three-dimensional Monte Carlo simulations are also performed for the experiments and they show a good agreement with the observed results. The deceleration-bunch operation mode presented here can find applications in the fields of cold collisions, high-resolution spectroscopy, and precision measurements.