Surface-electrode decelerator and deflector for Rydberg atoms and molecules

A surface-electrode decelerator and deflector for Rydberg atoms and molecules has been developed with the goal of performing collisional experiments. Translationally cold ${\mathrm{H}}_2$ molecules in a supersonic beam were excited to Rydberg-Stark states of principal quantum number $n=31$, loaded into electric traps moving at a predetermined speed above the surface of a bent printed circuit board, decelerated, and deflected from the original direction of the supersonic beam by an angle of ${10}^{\circ }$. The phase-space characteristics of the deflected beam were characterized by measuring the time-of-flight distribution and images of the Rydberg molecules and comparing them to the results of numerical particle-trajectory simulations. More than 1000 ${\mathrm{H}}_2$ molecules were deflected per experimental cycle at a repetition rate of 25 Hz. The phase-space characteristics of the deflector make it attractive to study ion-molecule reactions at low collision energies.

Figure 1

Schematic of the surface-electrode deflector used to deviate ${\mathrm{H}}_2$ Rydberg molecules in a supersonic beam by ${10}^{\circ }$ from the initial beam-propagation axis. (i) Photoexcitation region where the Rydberg molecules are prepared in the homogeneous electric field generated by applying a dc electric potential to two parallel planar electrodes separated by 4 mm. (ii) A 50-mm-long printed circuit board with 50 equidistant copper electrodes. The first 4-mm-long and the last 3.5-mm-long sections along the beam propagation axis are planar whereas the middle 42.5-mm-long section forms an arc of a circle with a radius of 244 mm. (iii) MCP detector with an anode connected to a phosphor screen and a CCD camera for imaging.

Figure 2

(a) Longitudinal velocity distribution of the beam obtained without applying any waveforms to the surface electrodes. (b) Longitudinal velocity distributions of the deflected ${\mathrm{H}}_2$ Rydberg molecules [($n=31,k=13–17$)] guided over the chip at velocities $v_0$ [determined with Eq. (3)] ranging from 1250 to 1340 m/s using waveforms with 80-V amplitude. Black traces: experimental results. Red traces: results of particle-trajectory simulations.

Figure 3

Spatial distribution of the ${\mathrm{H}}_2$ Rydberg molecules ($n=31,k=7–11$) detected at the imaging MCP detector following deflection at a constant velocity of 1290 m/s using waveform amplitudes of (a) 80 V, (b) 60 V, and (c) 40 V. (d) to (f) Corresponding images generated from particle-trajectory simulations. See text for details.

Figure 4

Velocity distributions of the ${\mathrm{H}}_2$ Rydberg molecules ($n=31,k=7–11$) along the (a) $X^{\prime }$ and (b) $Z^{\prime }$ directions following deflection at a constant velocity of 1290 m/s as a function of the applied waveform amplitude. The results of particle-trajectory simulations are indicated by squares, and the experimental results are indicated by circles.

Figure 5

Phase-space distributions of the deflected ${\mathrm{H}}_2$ Rydberg molecules ($n=31,k=7–11$) obtained from particle-trajectory simulations for waveform amplitudes of (a)–(c) 40 V and (d)–(f) 80 V. The black dots in the left and right parts of each plot correspond to Rydberg molecules at the beginning and the end of the deflector, respectively. The area shaded in gray corresponds to the phase-space areas explored over the entire deflection process. The distribution of spatial position is plotted with respect to the center of the trap ($X_{\mathrm{trap}},Y_{\mathrm{trap}},Z_{\mathrm{trap}}$).

Figure 6

Velocity distributions obtained after simultaneous deflection of a beam of ${\mathrm{H}}_2$ Rydberg molecules ($n=31,k=7–11$) by ${10}^{\circ }$ and deceleration from an initial velocity of 1300 m/s to final velocities of 1100, 900, 800, and 700 m/s.