Loading Stark-decelerated molecules into electrostatic quadrupole traps

Beams of neutral polar molecules in a low-field seeking quantum state can be slowed down using a Stark decelerator, and can subsequently be loaded and confined in electrostatic quadrupole traps. The efficiency of the trap loading process is determined by the ability to couple the decelerated packet of molecules into the trap without loss of molecules and without heating. We discuss the inherent difficulties to obtain ideal trap loading, and describe and compare different trap loading strategies. A new "split-endcap" quadrupole trap design is presented that enables improved trap loading efficiencies. This is experimentally verified by comparing the trapping of OH radicals using the conventional and the new quadrupole trap designs

Electrostatic trapping of metastable NH molecules

We report on the Stark deceleration and electrostatic trapping of $^{14}$NH ($a ^1\Delta$) radicals. In the trap, the molecules are excited on the spin-forbidden $A ^3\Pi \leftarrow a ^1\Delta$ transition and detected via their subsequent fluorescence to the $X ^3\Sigma^-$ ground state. The 1/e trapping time is 1.4 $\pm$ 0.1 s, from which a lower limit of 2.7 s for the radiative lifetime of the $a ^1\Delta, v=0,J=2$ state is deduced. The spectral profile of the molecules in the trapping field is measured to probe their spatial distribution. Electrostatic trapping of metastable NH followed by optical pumping of the trapped molecules to the electronic ground state is an important step towards accumulation of these radicals in a magnetic trap.Comment: replaced with final version, added journal referenc

Reflection of OH molecules from magnetic mirrors

We have reflected a Stark-decelerated beam of OH molecules under normal incidence from mirrors consisting of permanent magnets. Two different types of magnetic mirrors have been demonstrated. A long-range flat mirror made from a large disc magnet has been used to spatially focus the reflected beam in the longitudinal direction ("bunching"). A short-range curved mirror composed of an array of small cube magnets allows for transverse focusing of the reflected beam.Comment: 10 pages, 5 figure

Optical pumping of trapped neutral molecules by blackbody radiation

Optical pumping by blackbody radiation is a feature shared by all polar molecules and fundamentally limits the time that these molecules can be kept in a single quantum state in a trap. To demonstrate and quantify this, we have monitored the optical pumping of electrostatically trapped OH and OD radicals by room-temperature blackbody radiation. Transfer of these molecules to rotationally excited states by blackbody radiation at 295 K limits the $1/e$ trapping time for OH and OD in the $X^{2}\Pi_{3/2},v''=0,J''=3/2(f)$ state to 2.8 s and 7.1 s, respectively.Comment: corrected small mistakes; added journal reference

The radiative lifetime of metastable CO (a3Π,v=0a^3\Pi, v=0)

We present a combined experimental and theoretical study on the radiative lifetime of CO in the $a^3\Pi_{1,2}, v=0$ state. CO molecules in a beam are prepared in selected rotational levels of this metastable state, Stark-decelerated and electrostatically trapped. From the phosphorescence decay in the trap, the radiative lifetime is measured to be $2.63\pm0.03$ ms for the $a^3\Pi_1, v=0, J=1$ level. From spin-orbit coupling between the $a^3\Pi$ and the $A^1\Pi$ state a 20% longer radiative lifetime of 3.16 ms is calculated for this level. It is concluded that coupling to other $^1\Pi$ states contributes to the observed phosphorescence rate of metastable CO.Comment: replaced with final version, added journal referenc

Optimizing the Stark-decelerator beamline for the trapping of cold molecules using evolutionary strategies

We demonstrate feedback control optimization for the Stark deceleration and trapping of neutral polar molecules using evolutionary strategies. In a Stark-decelerator beamline pulsed electric fields are used to decelerate OH radicals and subsequently store them in an electrostatic trap. The efficiency of the deceleration and trapping process is determined by the exact timings of the applied electric field pulses. Automated optimization of these timings yields an increase of 40 % of the number of trapped OH radicals.Comment: 7 pages, 4 figures (RevTeX) (v2) minor corrections (v3) no changes to manuscript, but fix author list in arXiv abstrac

LIFETIME MEASUREMENTS WITH ELECTROSTATICALLY TRAPPED COLD MOLECULES

Author Institution: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, GermanyWith a Stark decelerator, bunches of state-selected molecules with a controlled velocity and with longitudinal temperatures as low as a few mK can be produced. These slow bunches of molecules can subsequently be trapped in an electrostatic trap. We will report on the deceleration and trapping of ground state OH, and metastable CO and NH molecules. The OH radicals are trapped at a density of $10^7 - 10^8$ cm$^{-3}$ and at a temperature of around 50 mK, and their trap lifetime is measured to be 2.8 s. The long interaction time afforded by the trap can be exploited to measure lifetimes of vibrationally excited states or electronically excited metastable states. Such lifetimes can be used as an accurate test of theoretical models. We will present experiments on the lifetime of OH ($X^2 \Pi_{3/2}) , v=1$ and of metastable CO ($a ^3 \Pi,v=0$). The different loss processes that play a role in the trap, like optical pumping by blackbody radiation, were studied in detail.\\ [1] S.Hoekstra \emph{et al.}, Optical pumping of trapped neutral molecules by blackbody radiation, Phys.~Rev.~Lett. \textbf{98} 13301 (2007) \ [2] J.~J.~Gilijamse \emph{et al.}, The radiative lifetime of metastable CO ($a ^3 \Pi,v=0$), J.~Chem.~Phys. \textbf{127} 221102 (2007)

DECELERATION, TRAPPING AND ACCUMULATION OF NH MOLECULES

Author Institution: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, GermanyWe report on the Stark-deceleration and electrostatic trapping of metastable NH molecules. Furthermore the progress towards higher densities of cold neutral molecules by accumulation of multiple Stark-decelerated packets of NH molecules in a magnetic trap will be presented. NH molecules in the long-lived metastable $a^{1}\Delta (v=0, J=2)$ state are ideally suited for Stark deceleration experiments because of their relatively large Stark shift and low mass. The metastable molecules $(\tau > 2.7 s)$ are produced in a supersonic expansion with a velocity of $\sim 450$ m/s, and are decelerated to a standstill by a 108-stage decelerator. Subsequently the metastable molecules are trapped electrostatically, with a temperature of about $50 - 100$ mK, a density of $\sim 10^{6}$ cm$^{-3}$ and a $1/e$ trapping lifetime of $1.4$ s. Following the deceleration and trapping, the metastable NH molecules are detected by the excitation of a spin-forbidden transition, resulting in spontaneous decay to the electronic ground state ($X^{3}\Sigma^{-}$). The electronic ground state has a negligible Stark shift, but can be trapped magnetically. The first experiments on the accumulation of ground state NH molecules in a magnetic trap will be presented.\\ [1] S.~Hoekstra \emph{et al.}, Electrostatic trapping of metastable NH molecules, Phys.~Rev.~A. \textbf{76} 063408 (2007