Electrostatic Trapping of ${\mathrm{N}}_2$ Molecules in High Rydberg States

${\mathrm{N}}_2$ molecules traveling in pulsed supersonic beams have been excited from their $\mathrm{X}{}^1{\mathrm{\Sigma }}_{\mathrm{g}}^{+}$ ground electronic state to long-lived Rydberg states with principal quantum numbers between 39 and 48 using a resonance-enhanced two-color three-photon excitation scheme. The Rydberg states populated had static electric dipole moments exceeding 5000 D which allowed deceleration of the molecules to rest in the laboratory-fixed frame of reference and three-dimensional trapping using inhomogeneous electric fields. The trapped molecules were confined for up to 10 ms, with effective trap decay time constants increasing with principal quantum number, and ranging from 450 to $700\mathrm{\mu }\mathrm{s}$. These observations, and comparison with the results of similar measurements with He atoms, indicate that the decay dynamics of the trapped Rydberg ${\mathrm{N}}_2$ molecules are dominated by spontaneous emission and do not exhibit significant contributions from effects of intramolecular interactions that lead to non-radiative decay.

Figure 1

(a) Schematic diagram of Rydberg-Stark decelerator. (b) Resonance-enhanced two-color three-photon excitation scheme used to populate long-lived Rydberg states in ${\mathrm{N}}_2$.

Figure 2

Laser photoexcitation spectra recorded by delayed PFI with (a) the decelerator off and detection on the molecular beam axis at $t_{\mathrm{PFI}}=130\mathrm{\mu }\mathrm{s}$, and (b) following deceleration and electrostatic trapping for $t_{\mathrm{trap}}=100\mathrm{\mu }\mathrm{s}$.

Figure 3

TOF distributions of Rydberg ${\mathrm{N}}_2$ molecules excited on the $43\mathrm{f}(N^{+}=J^{\prime })$ resonance with ${\upsilon }_2=26767.10{\mathrm{cm}}^{-1}$. Data recorded with the decelerator off are indicated by the dashed black curve with a maximum close to $130\mathrm{\mu }\mathrm{s}$. Measurements made with the decelerator on to guide the molecules at $800{\mathrm{ms}}^{-1}$ (red curve) and decelerate them from $v_{\mathrm{i}}=800\mathrm{m}{\mathrm{s}}^{-1}$ to $v_{\mathrm{f}}=500$, 300, and $100\mathrm{m}{\mathrm{s}}^{-1}$ are also shown.

Figure 4

Decay of Rydberg ${\mathrm{N}}_2$ molecules from the electrostatic trap for trapping times up to (a) 10 ms, and (b) 1 ms. The black dashed line in (a) represents the standard deviation of the background signal. The molecules were photoexcited on the $43\mathrm{f}(N^{+}=J^{\prime })$ resonance (${\upsilon }_2=26767.10{\mathrm{cm}}^{-1}$) in (a) and (b), or the $39\mathrm{f}(N^{+}=J^{\prime })$ resonance (${\upsilon }_2=26754.21{\mathrm{cm}}^{-1}$) in (b). In (b) single exponential functions fit to the data between $t_{\mathrm{trap}}=50$ and $500\mathrm{\mu }\mathrm{s}$ are indicated by the dashed curves. (c) Effective trap decay time constants, ${\tau }^{*}$, for molecules excited on $n\mathrm{f}(N^{+}=J^{\prime })$ resonances to long-lived $n(N^{+}=J^{\prime })$ Rydberg-Stark states. The continuous orange line represents the function ${\tau }^{*}=1.34n^{1.62}\mathrm{\mu }\mathrm{s}$ fit to the data.