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Physical Review Letters

Ionizing Collisional Rate of Metastable Rare-Gas Atoms in an Optical Lattice

Hideyuki Kunugita, T. Ido, Fujio Shimizu

Published Jul 28, 1997• 17 citations
Publisher

Abstract

Ionizing collisional rate of metastable krypton and argon atoms in an optical lattice ${k}_{\mathrm{lattice}}$ is compared with that in free space ${k}_{\mathrm{free}}$. Reduction of the collisional rate is observed for krypton atoms. However, the magnitude of reduction is no more than a factor of 2 at the laser detuning of 7 GHz. The ratio ${k}_{\mathrm{lattice}}/{k}_{\mathrm{free}}$ is found to change proportional to the square root of the excitation rate of atoms from the ${1s}_{5}$ metastable state to the ${2p}_{9}$ state by the lattice laser. The mechanism that prevents a larger reduction is discussed.

DOI
10.1103/physrevlett.79.621

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Collisions between rare-gas atoms in the 3 P 2 metastable state and in the ground state were studied. The metastable atoms were created by a discharge and oriented by optical pumping, and pressure broadening of their magnetic-resonance curves was measured. For xenon, mixtures of even and odd isotopes were used, leading to a determination of the cross section for metastability-exchange collisions. For krypton the results are reported for the disorientation of the metastable state in the natural gas. In addition the disorientation cross section has been measured of the krypton metastable state through collisions with helium.

Journal of Physics B Atomic and Molecular Physics•Aug 1, 1977•13 citations
Ionizing collisional rate of metastable krypton and argon atoms in an optical lattice klattice{k}_{\mathrm{lattice}}klattice​ is compared with that in free space kfree{k}_{\mathrm{free}}kfree​. Reduction of the collisional rate is observed for krypton atoms. However, the magnitude of reduction is no more than a factor of 2 at the laser detuning of 7 GHz. The ratio klattice/kfree{k}_{\mathrm{lattice}}/{k}_{\mathrm{free}}klattice​/kfree​ is found to change proportional to the square root of the excitation rate of atoms from the 1s5{1s}_{5}1s5​ metastable state to the 2p9{2p}_{9}2p9​ state by the lattice laser. The mechanism that prevents a larger reduction is discussed.
Ionizing collisional loss rate of the metastable argon and krypton atoms in an optical lattice is compared with the rate of atoms in free space as a function of lattice laser detuning. Contrary to a simple picture of the isolation of atoms by the lattice potential, our experimental result shows that the collision rate in optical lattice is always larger than that in free space except at a large laser detuning of ∼10 3 transition linewidth. Comparing the experimental result with the theoretical values that are derived from the classical trajectory calculation of the atom, we found that the optical pumping to non-trapped adiabatic potential surface prevents the collision suppression because it keeps the number of non-trapped atoms to a finite value even at low excitation rate.
The line shape of laser-induced ionizing collisions of ultracold Kr gas is investigated near the 1s5[4p55s:3P2]{1s}_{5}[4p^{5}5s:^{3}P_{2}]1s5​[4p55s:3P2​] and 2p9[4p55p:3D3]{2p}_{9}[4p^{5}5p:^{3}D_{3}]2p9​[4p55p:3D3​] transition. The rate increases several times when the laser is red tuned by a few times of the natural width, while it sharply decreases for a slight blue detuning. This frequency dependence of the collision rate is due to the collision dynamics characteristic of ultracold atoms in a near-resonant light. Our experimental results on metastable Kr atoms show a good qualitative agreement with semiclassical Monte Carlo simulation of the cold collision dynamics.
Abstract The collision between a spin-polarized metastable argon atom in Ar* (3p 5 4s, 3 P 2 , M = +2) state slightly decelerated by the Zeeman slower-laser technique and a co-propagating thermal ground state argon atom Ar (3p 6 , 1 S 0 ), both merged from the same supersonic beam, but coming through adjacent slots of a rotating disk, is investigated at the center of mass energies ranging from 1 to 10 meV. The duration of the laser pulse synchronised with the disk allows the tuning of the relative velocity and thus the collision energy. At these sub-thermal energies, the ‘resonant metastability transfer’ signal is too small to be evidenced. The explored energy range requires using indiscernibility amplitudes for identical isotopes to have a correct interpretation of the experimental results. Nevertheless, excitation transfers are expected to increase significantly at much lower energies as suggested by previous theoretical predictions of potentials 2g( 3 P 2 ) and 2u( 3 P 2 ). Limits at ultra-low collisional energies of the order of 1 mK (0.086 μ eV) or less, where gigantic elastic cross sections are expected, will also be discussed. The experimental method is versatile and could be applied using different isotopes of Argon like 36 Ar combined with 40 Ar, as well as other rare gases among which Krypton should be of great interest thanks to the available numerous isotopes present in a natural gas mixture.
We have investigated a new scheme for excitation of the 5s, J = 2 metastable level of Kr (5s[3/2] J = 2 ) which can be readily extended to other rare gases. In the scheme, an ultraviolet (UV) lamp is used to create a population of Kr atoms in the 5s[3/2] J = 1 level in a gas cell. The excited atoms are then pumped to the 5p[3/2] J = 2 level, using 819 nm light from a Ti:sapphire laser, from which they decay to the metastable state with a branching ratio of 77%. We made two striking observations: (1) the laser power required to saturate the second step decreases markedly as a function of gas cell pressure, and (2) the UV photon flux is converted with very high efficiency (≈10%) to metastable atom flux. A Monte Carlo study of the scattering of UV photons in the cell reproduces the trends observed. The understanding achieved points to the design of a higher flux source of metastable atoms.
We demonstrate the generation of metastable krypton in the long-lived 1s^{5} state using laser excitation. The atoms are excited through a two-photon absorption process into the 2p^{6} state using a pulsed optical parametric oscillator laser operating near 215 nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75%. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photoionization and two-photon absorption cross sections. When compared to traditional approaches to metastable production, this approach shows great potential for high-density metastable krypton production with minimal heating of the sample. Here, we show metastable production efficiencies of up to 2% per pulse. The new experimental results gained here, when combined with the density matrix model we have developed, suggest that fractional efficiencies up to 30% are possible under optimal conditions.
Collisions between rare-gas atoms in the 3 P 2 metastable state and in the ground state were studied. The metastable atoms were created by a discharge and oriented by optical pumping, and pressure broadening of their magnetic-resonance curves was measured. For xenon, mixtures of even and odd isotopes were used, leading to a determination of the cross section for metastability-exchange collisions. For krypton the results are reported for the disorientation of the metastable state in the natural gas. In addition the disorientation cross section has been measured of the krypton metastable state through collisions with helium.