The deceleration of molecules from cold molecular beams using electric and magnetic fields has become an important means for producing stationary, cold dipolar or paramagnetic molecular gases that can be trapped and potentially cooled to ultra-cold temperatures in the μK range. We report on a general scheme for the creation of cold molecules of essentially any type by deceleration of a cold molecular beam using intense optical fields. Deceleration of benzene molecules to zero velocity is achieved by utilizing a single half oscillation of the center-of-mass motion of the molecules within a moving optical lattice. The lattice traveling at half the speed of the molecular beam is created by the interference of two near-counter-propagating fields at different frequencies. We show that by rapidly switching on the optical lattice for approximately the time required for a half oscillation, a bunch of approximately 10 5 benzene molecules can be rapidly decelerated and brought to rest in the laboratory frame.
The deceleration of molecules from cold molecular beams using electric and magnetic fields has become an important means for producing stationary, cold dipolar or paramagnetic molecular gases that can be trapped and potentially cooled to ultra-cold temperatures in the μK range. We report on a general scheme for the creation of cold molecules of essentially any type by deceleration of a cold molecular beam using intense optical fields. Deceleration of benzene molecules to zero velocity is achieved by utilizing a single half oscillation of the center-of-mass motion of the molecules within a moving optical lattice. The lattice traveling at half the speed of the molecular beam is created by the interference of two near-counter-propagating fields at different frequencies. We show that by rapidly switching on the optical lattice for approximately the time required for a half oscillation, a bunch of approximately 10 5 benzene molecules can be rapidly decelerated and brought to rest in the laboratory frame.
This work presents the proposed schemes for decelerating cold molecules created in pulsed supersonic expansions using pulsed optical lattices. The first scheme relies on the application of a decelerating optical lattice with a dipole-potential well depth of approximately 1 K, created by rapidly chirping medium-intensity fields in the 10 W/cm/sup 2/ range. This scheme is an optical analog of the Start decelerator that has been successfully used to slow a range of polar molecules. A significant fraction (about 10%) of the very heavy I/sub 2 /molecules in an Ar buffer gas is shown to be slowed by using this method over sub-microsecond time scales. In the second technique, an optical lattice with larger well depth in the 100 K range travelling at half the supersonic beam velocity is used to trap a significant fraction of the cold, high-velocity molecules. This technique is developed based on the property of periodic motion of the trapped molecules in the optical lattice; the molecules reverse their initial (relative) velocities in the lattice reference frame after half a period. Using this method the cold molecules can be transferred from high speed to zero velocity on nanosecond time scales. As an example, 33% of a CO molecule beam (1 K) with a velocity of 230 m/s is slowed utilising optical intensities of less than 10/sup 12/ W/cm/sup 2/.
We describe the deceleration of nitric oxide, benzene and xenon atoms in a molecular beam using one-dimensional pulsed optical lattices created by fields with intensities in the 1012 W cm−2 range. We show that for the same pulse duration and lattice intensity the velocity of the molecules can be controlled by tailoring the lattice velocity. By utilizing the time-dependent oscillatory motion of the molecules within the lattice, we demonstrate the deceleration of nitric oxide from an initial velocity of 400 m s−1 to a final velocity of 290 m s−1 in a single 5.8 ns pulse. Using higher intensities, we measure the deceleration of benzene molecules from 380 m s−1 to 191 m s−1, representing a 75% reduction in the kinetic energy within the lattice over the same duration.
Research of cold and ultracold molecules is currently a burgeoning field in experimental and theoretical physics. New experimental techniques, involving an increasingly large set of molecule types under high levels of control, are currently opening up new avenues of research with a vast array of potential applications. From understanding the role of quantum mechanics in molecular scattering and cold chemistry, to testing the fundamental symmetries of nature and realizing quantum computing with dipolar molecular qubits, experiments are accessing regimes not dreamed of even a few years ago. Theoretical interest and computing capabilities are also at an all time high, spurred on by the possibility of creating ultracold dipolar gases as tunable realizations of strongly interacting quantum Hamiltonians, creating exotic phases of matter, and the investigation of controlling molecular interactions with applied electromagnetic fields.\nLess than a decade ago, cold molecule experiments had seemingly reached a technological plateau, being capable of creating moderate densities of 106-107 molecules/cm3 at temperatures of 10-100 mK. With many applications requiring colder temperatures and higher densities, the field was ripe for new advances. Today, via a plethora of methods such as direct molecular laser cooling, electro-optical cooling, magneto- and photo-association, and new molecular beam deceleration techniques, the field is just beginning to have the tools capable of producing truly interesting systems for study.\nThis work will discuss a couple of major steps taken in the direction of achieving scientific goals using cold molecules. The first experimental advancement discussed will be the development of a co-trap environment for studying interactions and collisions between ultracold atoms and Stark decelerated cold polar molecules. In this experiment, rubidium atoms are trapped using magnetic fields, and ammonia atoms are decelerated and trapped using electric fields. The two traps are spatially overlapped in order to investigate inter-species interactions. The co-trap environment provides exceedingly long interaction times, many orders of magnitude longer than typical beam-based interaction studies. As a result, it provides extremely high sensitivity to weak interaction mechanisms. The second experimental advancement discussed will be the development and construction of a new style of Stark decelerator, capable of producing much larger densities of cold molecules. This apparatus has the potential to expand the realm of possible experiments with chemically interesting species, and provide an unprecedented amount of control over molecular beams and traps. The gains haven't come easily though, as a new class of custom high-voltage amplifiers have needed to be developed. This part of the experiment alone took approximately two years of consistent effort to bring to fruition. After many years of development, this experiment is poised to come online, finally fulfilling its potential.
According to the optical Stark deceleration theory of using a stationary quasi-cw red-detuned optical lattice to slow and trap an arbitrary pulsed molecular beam, we propose a novel idea of using a modulated optical lattice instead of a stationary one to realize a multistage optical Stark deceleration. We analyze the motion of the decelerated molecules inside the optical decelerator, and study the dependence of the velocity of the decelerated molecular packet on the synchronous phase angle and the number of the deceleration stages (i.e. half the number of the optical-lattice cells) by using the Monte-Carlo method. The simulation results show that it takes longer time for the molecules to reach the detector as the number of the deceleration stages increases. The decelerated molecular wave packets are gradually separated from the large wave packets of the original molecular velocity distribution. And the higher the number of the deceleration stages, the lower the decelerated molecular speed is. In addition, we also study the influence of the initial phase angle of synchronous molecules under the same conditions. It is demonstrated that the higher the initial phase angle of synchronous molecules, the lower the decelerated molecular speed is and the smaller the number of molecules in the deceleration wave packet, so the phase space is compressed. The result also shows that the modulated optical Stark decelerator does not have the process of molecular free flight, and thus improving the efficiency of deceleration for molecules. The ultra-cold molecules can be trapped in the optical lattice by rapidly turning off the modulation signal of the lattice. Comparing with the previous scheme, the doubled number of the deceleration stages is reached in the same optical lattice length since a modulated optical lattice is used. For a length of optical lattice of 3.71 mm, theoretical simulation results demonstrate that the speed of methane molecules is decelerated from 280 m/s to 172 m/s. Comparing with the previous results from 280 m/s to 232 m/s, the deceleration effect is improved by 26%. Our scheme can not only obtain an ultra-colder molecular packet under the same molecular-beam parameters and deceleration conditions, but also be directly used to trap the slowed cold molecules after the deceleration without needing to use other techniques for molecular trapping.
We study the creation of stationary cold molecules by rapid deceleration of supersonically cooled molecules in a high-intensity pulsed optical lattice. Using the heavy molecule I2 as an example we predict the evolution of the velocity distribution function of the ensemble during the deceleration period, and show that stationary cold molecules with temperatures below 1 K and densities of approximately ${10}^{12}{\mathrm{cm}}^{\ensuremath{-}3}$ can be produced over length scales of hundreds of micrometers on submicrosecond time scales.
We propose a promising scheme to realize the deceleration of a pulsed subsonic molecular beam by using a multistage optical Stark decelerator (i.e., a 1D quasi-cw traveling optical lattice), which is composed of two nearly counter-propagating, time-varying, red-detuned light fields with an intensity of ~10⁷Wcm⁻² and a fixed frequency difference between them. We also study the influence of the velocity reduced amount of the traveling lattice, the lattice power, the synchronous phase angle, the deceleration-stage number and the temporal profile of laser pulses on the molecular slowing results by using 3D Monte-Carlo method. Our study shows that the proposed decelerator cannot only be used to slow a pulsed subsonic beam from 240m/s to standstill, but also to obtain a cold molecular packet with a temperature of a few µK, and the corresponding fraction of cold molecules is 10⁻⁶-10⁻⁷, which strongly depends on the synchronous phase angle. And we also find that a pair of appropriate rising and falling times of laser pulses will lead to a better slowing effect than that produced by the top-hat temporal ones.