Diffraction-free vectorial elliptic hollow beams(vEHBs)are generated by an optical system composed of a short elliptic hollow fiber(EHF)and an axicon.Each beam has a closed elliptic annular intensity profile and space-varying polarization states in its diffraction-free distance of more than 1 m.The generated beams have a counter-clockwise or clockwise periodically-rotated inhomogeneous polarization.And the spin angular momentum(SAM)of the vEHBs is 1ħor-1ħwhich is consistent with the type of dual-mode in the EHF and the periodic polarization rotations of the vEHBs.The vEHBs have potential applications in optically trapping and micromanipulating the micro-or nano-particles,quantum information transmission,and Bose-Einstein condensates,etc.
We demonstrate the production of cold, slow NH_3 molecules from a supersonic NH_3 molecular beam using our electrostatic Stark decelerator consisting of 179 slowing stages. By using this long Stark decelerator, a supersonic NH_3 molecular beam can be easily decelerated to trappable velocities. Here we present two modes for operating the Stark decelerator to slow the supersonic NH_3 molecules. The first is the normal mode, where all 179 stages are used to decelerate molecules, and it allows decelerating the NH_3 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 NH_3 beam from 333 m/s to 24 m/s,with a final temperature of 2.9 m K. 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.
We demonstrate a scheme to use a Littman configuration external cavity diode laser(ECDL) as a stablefrequency light source to stabilize two cw single-mode Ti:sapphire lasers for laser cooling of magnesium fluoride molecules. An ECDL based on the Littman configuration is constructed and stabilized by a digital signal processor system. We stabilize the frequency of our ECDL to 0.77 MHz precision over 10 h and the Allan standard deviation reaches 2.6 × 10-11 at an integration time of 10 s. We lock two Ti:sapphire lasers through a transfer cavity, and either laser has a long-term frequency stability of 2.5 MHz.
We propose a novel scheme of optical confinement for atoms by using a concave grating reflector.The two-dimension grating structure with a concave surface shape exhibits strong focusing ability under radially polarized illumination.Especially,the light intensity at the focal point is about 100 times higher than that of the incident light.Such a focusing optical field reflected from the curved grating structure can provide a deep potential to trap cold atoms.We discuss the feasibility of the structure serving as an optical dipole trap.Our results are as follows.(i) Van der Waals attraction potential to the surface of the structure has a low effect on trapped atoms,(ⅱ) The maximum trapping potential is ~1.14 mK in the optical trap,which is high enough to trap cold ^(87)Rb atoms from a standard magneto-optical trap with a temperature of 120 μK,and the maximum photon scattering rate is lower than 1/s.(ⅲ) Such a microtrap array can also manipulate and control cold molecules,or microscopic particles.
Two novel electrostatic traps named octopole-based disk electrostatic trap(ODET)and tubular-based disk electrostatic trap(TDET)are proposed for trapping cold polar molecules in low-field-seeking states.Using MgF as the target molecule,single loading and multi-loading methods are numerically simulated with varied incident velocities of slow molecular beams in the two types of traps,respectively.In ODET,with an incident velocity of 10 m/s,a highest loading efficiency of 78.4% or 99.9% has been achieved under the single loading or multi-loading operation mode.In TDET,with an incident velocity of 11 m/s,a highest loading efficiency of 81.6% or 106.5% has been achieved using the two loading methods,respectively.With such high loading efficiencies,the trapped cold molecules can be applied in the researches of cold collisions,high precision spectroscopy,and precision measurements.Especially,together with a blue-detuned hollow beam,the new electrostatic traps proposed here offer a new platform for the following gradient-intensity cooling of MgF molecules,which may provide a new way to produce high density ultracold molecules.
An electrostatic trap for polar molecules is proposed. Loading and trapping of polar molecules can be realized by applying different voltages to the two electrodes of the trap. For ND3 molecular beams centered at ～10 m/s, a high loading efficiency of ～67% can be obtained, as confirmed by our Monte Carlo simulations. The volume of our trap is as large as ～3.6 cm3, suitable for study of the adiabatic cooling of trapped molecules. Our simulations indicate that trapped ND3 molecules can be cooled from ～23.3 m K to 1.47 m K by reducing the trapping voltages on the electrodes from 50.0 k V to1.00 k V.
