We present a compact electrostatic device for producing velocity-controlled bunches of cold molecular ions. In our implementation, BaF molecules are generated in a supersonic expansion and photoionized inside a stack of electrodes providing >99% field homogeneity. Short voltage pulses applied across the structure decelerate the resulting BaF+ ions by several hundred meters per second over only a few millimeters, enabling control of the mean velocity down to the meV regime while preserving a narrow velocity spread. The setup delivers bunches of thousands of ions and thus provides a versatile source for ion-neutral collision studies, high-resolution spectroscopy, and efficient trap loading. Although the present work does not address rovibrational state preparation, threshold photoionization techniques could be straightforwardly combined with this approach to generate ions in a well-defined internal distribution. The instrument, therefore, offers a simple and general route to the controlled preparation of cold molecular ion beams for a broad range of applications in atomic and molecular physics.
We present a compact electrostatic device for producing velocity-controlled bunches of cold molecular ions. In our implementation, BaF molecules are generated in a supersonic expansion and photoionized inside a stack of electrodes providing >99% field homogeneity. Short voltage pulses applied across the structure decelerate the resulting BaF+ ions by several hundred meters per second over only a few millimeters, enabling control of the mean velocity down to the meV regime while preserving a narrow velocity spread. The setup delivers bunches of thousands of ions and thus provides a versatile source for ion-neutral collision studies, high-resolution spectroscopy, and efficient trap loading. Although the present work does not address rovibrational state preparation, threshold photoionization techniques could be straightforwardly combined with this approach to generate ions in a well-defined internal distribution. The instrument, therefore, offers a simple and general route to the controlled preparation of cold molecular ion beams for a broad range of applications in atomic and molecular physics.
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.
To meet some demands for realizing precise measurements of an electric dipole moment of electron (eEDM) and examining cold collisions or cold chemical physics, we have proposed a novel, versatile electrostatic Stark decelerator with an array of true 3D electric potential wells, which are created by a series of horizontally-oriented, U-shaped electrodes with time-sequence controlling high voltages (± HV) and two guiding electrodes with a constant voltage. We have calculated the 2D electric field distribution, the Stark shifts of the four lowest rotational sub-levels of PbF molecules in the X1(2)Π1/2(v = 0) electronic and vibrational ground states as well as the population in the different rotational levels. We have discussed the 2D longitudinal and transverse phase-space acceptances of PbF molecules in our decelerator. Subsequently, we have simulated the dynamic processes of the decelerated PbF molecules using the 3D Monte-Carlo method, and have found that a supersonic PbF beam with a velocity of 300 m s(-1) can be efficiently slowed to about 5 m s(-1), which will greatly enhance the sensitivities to research a parity violation and measure an eEDM. In addition, we have investigated the dependences of the longitudinal velocity spread, longitudinal temperature and bunching efficiency on both the number of guiding stages and high voltages, and found that after bunching, a cold packet of PbF molecules in the J = 7/2, MΩ = -7/4 state with a longitudinal velocity spread of 0.69 m s(-1) (corresponding to a longitudinal temperature of 2.35 mK) will be produced by our high-efficient decelerator, which will generate a high energy-resolution molecular beam for studying cold collision physics. Finally, our novel decelerator can also be used to efficiently slow NO molecules with a tiny electric dipole moment (EDM) of 0.16 D from 315 m s(-1) to 28 m s(-1). It is clear that our proposed new decelerator has a good slowing performance and experimental feasibility as well as wide applications in the field of precise measurements and cold molecule physics.
A supersonic beam source for SrF and BaF molecules is constructed by combining the expansion of carrier gas (a mixture of 2% SF6 and 98% argon) from an Even–Lavie valve with laser ablation of a barium/strontium metal target at a repetition rate of 10 Hz. Molecular beams with a narrow translational velocity spread are produced at relative values of Δv/v = 0.053(11) and 0.054(9) for SrF and BaF, respectively. The relative velocity spread of the beams produced in our source is lower in comparison with the results from other metal fluoride beams produced in supersonic laser ablation sources. The rotational temperature of BaF is measured to be 3.5 K. The source produces 6 × 108 and 107 molecules per steradian per pulse in the X2Σ+ (ν = 0, N = 1) state of BaF and SrF molecules, respectively, a state amenable to Stark deceleration and laser cooling.
We describe a versatile experimental apparatus designed for investigating ion-molecule reaction dynamics at low temperatures under ultra-high vacuum conditions (<8 × 10-11 Torr). The system integrates laser-cooled atomic ions confined in a linear Paul trap with a pulsed molecular beam featuring simultaneous quantum-state and velocity selection. Reaction products are identified using fluorescence imaging and a time-of-flight mass spectrometer. The setup accommodates a broad range of ionic and neutral species-including Be+, C+, H2, N2, O2, H2O, and others-enabling high-sensitivity studies of reaction dynamics. As a benchmark, we present measurements of the Be+ + H2 reaction across a range of collision energies, including reactions with H2 vibrationally excited to the v = 1 level. The apparatus offers fine control over both internal and external degrees of freedom, providing a general platform for cold ion-molecule reaction studies.
We propose a method to produce, in a pulsed or continuous way, cold samples of highly polar molecules. Using a pulsed or continuous standard (supersonic) beam of these molecules, our idea consists of transforming the molecules into their anionic counterparts, which are decelerated to a standstill by a well-controlled external electric field and ultimately neutralized. The neutral-to-anion transformation occurs through collisions with Rydberg atoms coming from an additional atomic beam. This Rydberg electron transfer process is possible provided that the molecular species has a sufficiently strong electric dipole ( D, i.e., cm). Whatever the mass of the species, the deceleration stage is realized by a temporally and spatially controlled electric field within a range of less than one centimeter, which is much shorter than in current deceleration experiments of neutral molecules. Once stopped, the molecular anions are neutralized by laser photodetachment or a pulsed electric field process. The resulting molecules might be held and accumulated, for instance, in a magnetic trap.
We investigate the deceleration and bunching of cold molecules in a pulsed supersonic jet using a far-off-resonant optical lattice traveling with a constant velocity. Using an analytical treatment, we show that by choosing the lattice velocity equal to half the supersonic beam velocity and by optimizing the pulse duration, a significant fraction $(\ensuremath{\sim}33%)$ of translationally cold (1 K) CO molecules from a supersonic molecular beam can be decelerated to zero velocity, and simultaneously bunched in velocity space. Due to the large difference of polarizability to mass ratio between the buffer gas and the CO molecules in the pulsed jet, the buffer gas can be precluded from the fraction of stationary molecules by choosing a suitable pulse duration. Furthermore, we find that spatial bunching within the optical lattice is induced and the position of the bunch within the lattice can be chosen by varying the lattice velocity.