N_{2} molecules traveling in pulsed supersonic beams have been excited from their X ^{1}Σ_{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 μs. These observations, and comparison with the results of similar measurements with He atoms, indicate that the decay dynamics of the trapped Rydberg 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.
N_{2} molecules traveling in pulsed supersonic beams have been excited from their X ^{1}Σ_{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 μs. These observations, and comparison with the results of similar measurements with He atoms, indicate that the decay dynamics of the trapped Rydberg 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.
Nitric oxide (NO) molecules in pulsed supersonic beams have been excited to long-lived Rydberg-Stark states in series converging to the lowest vibrational level in the ground electronic state of NO+ with rotational quantum numbers N+ = 2, 4, and 6. The molecules in these excited states were then guided, or decelerated and trapped in a chip-based Rydberg-Stark decelerator, and detected in situ by pulsed electric field ionization. Time constants, reflecting the decay of molecules in N+ = 2 Rydberg-Stark states, with principal quantum numbers n between 38 and 44, from the electrostatic traps were measured to be ∼300μs. Molecules in Rydberg-Stark states with N+ = 4 and 6, and the same range of values of n were too short-lived to be trapped, but their decay time constants could be determined from complementary sets of delayed pulsed electric field ionization measurements to be ∼100 and ∼25 μs, respectively.
Nitric oxide (NO) molecules initially traveling at 795 m/s in pulsed supersonic beams have been photoexcited to long-lived hydrogenic Rydberg-Stark states, decelerated and electrostatically trapped in a cryogenically cooled, chip-based transmission-line Rydberg-Stark decelerator. The decelerated and trapped molecules were detected in situ by pulsed electric field ionization. The operation of the decelerator was validated by comparison of the experimental data with the results of numerical calculations of particle trajectories. Studies of the decay of the trapped molecules on timescales up to 1 ms provide new insights into the lifetimes of, and effects of blackbody radiation on, Rydberg states of NO.
The interaction between inhomogeneous electric fields and the large electric dipole moments of atoms and molecules in Rydberg states of high principal quantum number can be used to efficiently accelerate and decelerate atoms and molecules in the gas phase. We describe here how hydrogen atoms and molecules initially moving with velocities of ∼600 m/s in supersonic beams can be decelerated to zero velocity and loaded into electric traps. The long observation times that are made possible by the electrostatic trapping enables one to study slow relaxation processes. Experiments are presented in which we have observed photoionization processes and transitions between Rydberg states induced by blackbody radiation at temperatures between 10 K and 300 K on a time scale of several milliseconds. Comparison of these processes in Rydberg states of H and H(2) suggests the importance, in H(2), of collisional processes and of the process of blackbody-radiation-induced predissociation.
The dynamics of nitric oxide (NO) molecules in a cryogenically cooled, transmission-line Rydberg-Stark decelerator have been studied experimentally and through numerical particle trajectory calculations. The molecules, initially travelling in pulsed supersonic beams, were prepared in states with principal quantum number n = 43, in the Rydberg series converging to the N+=2 rotational state of NO+ using the nℓ X+ 1Σ+←A 2Σ+←X 2Π1/2 resonance-enhanced two-colour two-photon excitation scheme. Deceleration from 795 m/s to rest in the laboratory-fixed frame of reference was achieved in a time of ∼250 μs. The observed motional dynamics of the decelerated and trapped Rydberg molecules is in good quantitative agreement with the results of the calculations. The translational temperature of the trapped molecules was determined to be ∼8 K from their rate of expansion after the trap was switched off. These results are of importance in the interpretation of measurements of lifetimes and decay processes of cold electrostatically trapped Rydberg molecules, and in the optimisation of the operation of this type of decelerator for heavier species.
Hydrogen atoms in supersonic expansions with velocities in the range from 700to800m∕s have been excited to Rydberg-Stark states with principal quantum number n between 20 and 40, decelerated to zero velocity in the lab frame using time-dependent inhomogeneous electric fields, and trapped in a two-dimensional electrostatic trap with an initial density of $\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. The motion of the atomic cloud in the trap was observed by measuring the times of flight and images of the H+ ions produced by pulsed field ionization. The velocity distribution of the trapped atoms can be described by an effective temperature of 350mK. The decay of the population of trapped atoms does not follow a single-exponential behavior and has contributions from radiative and collisional processes.
Abstract Supersonic beams of hydrogen atoms, prepared selectively in Rydberg–Stark states of principal quantum number n in the range between 25 and 35, have been deflected by 90 ◦ , decelerated and loaded into off-axis electric traps at initial densities of ≈ 10 6 atoms cm −3 and translational temperatures of 150 mK. The ability to confine the atoms spatially was exploited to study their decay by radiative and collisional processes. The evolution of the population of trapped atoms was measured for several milliseconds in dependence of the principal quantum number of the initially prepared states, the initial Rydberg-atom density in the trap, and the temperature of the environment of the trap, which could be varied between 7.5 and 300 K using a cryorefrigerator. At room temperature, the population of trapped Rydberg atoms was found to decay faster than expected on the basis of their natural lifetimes, primarily because of absorption and emission stimulated by the thermal radiation field. At the lowest temperatures investigated experimentally, the decay was found to be multiexponential, with an initial rate scaling as n − 4 and corresponding closely to the natural lifetimes of the initially prepared Rydberg–Stark states. The decay rate was found to continually decrease over time and to reach an almost n -independent rate of more than (1 ms) −1 after 3 ms. To analyze the experimentally observed decay of the populations of trapped atoms, numerical simulations were performed which included all radiative processes, i.e., spontaneous emission as well as absorption and emission stimulated by the thermal radiation. These simulations, however, systematically underestimated the population of trapped atoms observed after several milliseconds by almost two orders of magnitude, although they reliably predicted the decay rates of the remaining atoms in the trap. The calculations revealed that the atoms that remain in the trap for the longest times have larger absolute values of the magnetic quantum number m than the optically prepared Rydberg–Stark states, and this observation led to the conclusion that a much more efficient mechanism than a purely radiative one must exist to induce transitions to Rydberg–Stark states of higher ∣ m ∣ values. While searching for such a mechanism, we discovered that resonant dipole–dipole collisions between Rydberg atoms in the trap represent an extremely efficient way of inducing transitions to states of higher ∣ m ∣ values. The efficiency of the mechanism is a consequence of the almost perfectly linear nature of the Stark effect at the moderate field strengths used to trap the atoms, which permits cascades of transitions between entire networks of near-degenerate Rydberg-atom-pair states. To include such cascades of resonant dipole–dipole transitions in the numerical simulations, we have generalized the two-state Förster-type collision model used to describe resonant collisions in ultracold Rydberg gases to a multi-state situation. It is only when considering the combined effects of collisional and radiative processes that the observed decay of the population of Rydberg atoms in the trap could be satisfactorily reproduced for all n values studied experimentally.