Preparation of an ultra-cold sample of ammonia molecules for precision measurements

We present experiments in which an ultra-cold sample of ammonia molecules is released from an electrostatic trap and recaptured after a variable time. It is shown that, by performing adiabatic cooling before releasing the molecules and adiabatic re-compression after they are recaptured, we are able to observe molecules even after more than 10 ms of free expansion. A coherent measurement performed during this time will have a statistical uncertainty that decreases approximately as the inverse of the square root of the expansion time. This offers interesting prospects for high-resolution spectroscopy and precision tests of fundamental physics theories.

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.

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.

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

We present a combined experimental and theoretical study on the radiative lifetime of CO in the $a^3Pi_{1,2}, v=0$ 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 $2.63pm0.03$ ms for the $a^3Pi_1, v=0, J=1$ level. From spin-orbit coupling between the $a^3Pi$ and the $A^1Pi$ state a 20% longer radiative lifetime of 3.16 ms is calculated for this level. It is concluded that coupling to other $^1Pi$ states contributes to the observed phosphorescence rate of metastable CO.

Electrostatic trapping of metastable NH molecules

We report on the Stark deceleration and electrostatic trapping of $^{14}$NH ($a ^1Delta$) radicals. In the trap, the molecules are excited on the spin-forbidden $A ^3Pi leftarrow a ^1Delta$ transition and detected via their subsequent fluorescence to the $X ^3Sigma^-$ 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 $a ^1Delta, v=0,J=2$ 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.