Phase Space Manipulation of Cold Free Radical OH Molecules

We report bunching, slowing, and acceleration of a supersonically cooled beam of diatomic hydroxyl radicals (OH). In situ observation of laser-induced fluorescence along the beam propagation path allows for detailed characterization of longitudinal phase-space manipulation of OH molecules through the Stark effect by precisely sequenced inhomogeneous electric fields.

Figure 1

Upper panel: schematic of the Stark decelerator for free radical OH. Lower panel: (a) discharging light at nozzle; LIF signal, (b) before skimmer ($\times 0.01$), (c) after hexapole, (d) after 23 stages, (e) after 37 stages, (f) before 51 stages.

Figure 2

(a) Transverse guiding, (b) bunching, (c) deceleration, and (d) acceleration of OH after 14 stages of Stark slowing followed by 9 additional stages of transverse guiding. For the sake of clarity, the deceleration and acceleration data are shifted vertically. The peaks marked by arrows represent molecules trapped in the moving potential wells.

Figure 3

Measured time-of-flight distribution at (a) 23 stages and (b) 37 stages (22 and 36 stages of deceleration, respectively, followed by guidance for one stage). Also shown are instantaneous pictures of phase space distributions of OH after (c) 22 and (d) 36 stages of deceleration. In both (a) and (b), data points are red squares and theory thick blue lines.

Figure 4

OH molecules after 50 stages of transverse guidance (green diamonds), bunching (black squares), and deceleration (red circles). We note that experimental conditions fluctuate from day to day resulting in molecular number variations.