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Journal de Physique II

Investigations of a r.f. stored Ca+ ion cloud and observation of the S-D forbidden transitions

Martina Knoop, M. Vedel, F. Vedel

Published Oct 1, 1994• 7 citations
Publisher

Abstract

In order to exploit the capability of a high-Q transition for a frequency standard in the optical domain (729 nm), a stored Ca+ ion cloud in a medium-size ion trap is investigated. Long confinement times are obtained in the presence of helium as a buffer gas in the range 10-6-10-8 mbar and at a pseudopotential well depth of 62 eV. First observations of the electric quadrupole line were achieved by direct excitation of one of the first metastable doublet levels (τ≈1 s). Utilisation of a grating-stabilised diode laser in order to probe both levels when only one level is initially populated allows us to observe almost equal fluorescence intensities of both forbidden lines that show the presence of a strong fine structure mixing which exists in addition to quenching.

DOI
10.1051/jp2:1994222

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The electric quadrupole transition of confined Ca/sup +/ ions has been proposed as a frequency standard in the visible domain. To access metrologic conditions, we have built a cylindrical miniature trap, allowing to obtain high frequencies of motion and preparing the access to the Lamb-Dicke regime where the first order Doppler broadening is suppressed. Laser cooling and interrogation of the confined ions require lasers at 397 nm and at 729 nm. We propose the generation of these wavelengths using multimode laser diodes and a frequency-doubling set-up.

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Summary form only given. Among the ions proposed for a frequency standard in the optical domain, Ca/sup +/ is one of the most favorable candidates due to its wavelengths accessible with all-solid-state laser systems. This allows to imagine an ultimate experimental setup being simple and compact. The 4S/sub 1/2/-3D/sub 5/2/ electric quadrupole transition at 729 nm with a natural linewidth below 1 Hz serves as clock transition, while laser cooling on one of the resonance lines is carried out at 397 nm. To obtain the small spectral linewidths necessary for a frequency standard performance, it is essential to reduce the residual Doppler broadening caused by the RF heating in the Paul trap. The first-order Doppler broadening of a single ion can be eliminated in the Lamb-Dicke regime where the ion's amplitude of motion is inferior to the emitted wavelength. The main condition for the access of this frequency modulation regime is a high motional frequency of the trapped ion. This is more easily obtained in a low capacitance device and thus traps with reduced dimensions are required. We have set up a miniature ion trap of the Paul-Straubel-type. The stored ions are observed by a photomultiplier in the photon-counting mode as well as by an intensified CCD camera, permitting the visualization of their spatial behavior. Laser cooling of the Ca/sup +/ ions is carried out on the 4S/sub 1/2/-4P/sup 1/2/ resonance line at 397 nm. Progress on the characterization of the trapped single ion as well as on the generation of the involved wavelengths exclusively by solid-state lasers is reported.

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Collisional relaxation and fine-structure mixing rate constants have been measured for the metastable $D$ doublet ${(3D}_{3/2},$ ${3D}_{5/2})$ of ${\mathrm{Ca}}^{+}$ ions in the presence of different neutral gases completing a previous work. Experimental results are given for He, Ne, Ar, ${\mathrm{H}}_{2},$ ${\mathrm{N}}_{2},$ and ${\mathrm{CH}}_{4}.$ These data have been obtained with a cloud of approximately ${10}^{5}$ ${\mathrm{Ca}}^{+}$ ions stored in a Paul trap at kinetic energies of around 1 eV. The investigated levels were populated by direct excitation of the corresponding $4S\ensuremath{-}3D$ transitions. The involved time constants were determined from the temporal evolution of the fluorescence of one of the resonance transitions, following the optical pumping of the $P$ level from the $D$ component. Comparison of our data with other similar experimental and theoretical work is finally presented.

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The National Institute of Information and Communications Technology in Japan is proceeding with development of an optical frequency standard using an electric quadrupole transition of Ca+ ions in a small radio-frequency trap. The single, trapped 40Ca+ ions are laser cooled to a temperature of <10 mK using extended-cavity diode lasers at 397 nm and 866 nm. In order to measure the electric quadrupole transition, the linewidth of the clock laser diode at 729 nm is reduced to ~66 Hz using an ultra-low-expansion (ULE) cavity. We observed the electric quadrupole transition with a linewidth of ~600 kHz, together with the ionic motional sidebands. We are also developing optical frequency combs without photonic fibers broadening the spectrum. The experimental is now improved in order to observe the narrower linewidth of the quadrupole transition.

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Single Ca + Ion Trapping toward Precise Frequency Measurement of the 4 2 S 1/2 - 3 2 D 5/2 Transition

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Abstract —We are proceeding with a development of an optical frequency standard using a 2 S 1/2 – 2 D 5/2 electric quadrupole transition of Ca + ions in a small radio-frequency trap. We have theoretically confirmed that an uncertainty of <1 x 10 -15 is attainable in measurement of the 2 S 1/2 – 2 D 5/2 transition frequency. Experimentally, we have developed stable laser-diode systems and observed the quantum jump of single 40 Ca + ions to the 2 D 5/2 state. I. I NTRODUCTION The uncertainty of primary frequency standards using Cs atoms reaches around 10 -15 and the inherent limits involved in them are discussed. On the other hand, frequency standards using new materials and methods are proposed for developing more accurate frequency standards. Recently, several groups have measured frequencies of the ionic forbidden transitions in the optical region to apply them to the clock transitions of optical frequency standards [1]. We now proceeds with study on an optical frequency standard using single Ca

•Aug 31, 2005•2 citations
In order to exploit the capability of a high-Q transition for a frequency standard in the optical domain (729 nm), a stored Ca+ ion cloud in a medium-size ion trap is investigated. Long confinement times are obtained in the presence of helium as a buffer gas in the range 10-6-10-8 mbar and at a pseudopotential well depth of 62 eV. First observations of the electric quadrupole line were achieved by direct excitation of one of the first metastable doublet levels (τ≈1 s). Utilisation of a grating-stabilised diode laser in order to probe both levels when only one level is initially populated allows us to observe almost equal fluorescence intensities of both forbidden lines that show the presence of a strong fine structure mixing which exists in addition to quenching.
The electric quadrupole transition of confined Ca/sup +/ ions has been proposed as a frequency standard in the visible domain. To access metrologic conditions, we have built a cylindrical miniature trap, allowing to obtain high frequencies of motion and preparing the access to the Lamb-Dicke regime where the first order Doppler broadening is suppressed. Laser cooling and interrogation of the confined ions require lasers at 397 nm and at 729 nm. We propose the generation of these wavelengths using multimode laser diodes and a frequency-doubling set-up.
Summary form only given. Among the ions proposed for a frequency standard in the optical domain, Ca/sup +/ is one of the most favorable candidates due to its wavelengths accessible with all-solid-state laser systems. This allows to imagine an ultimate experimental setup being simple and compact. The 4S/sub 1/2/-3D/sub 5/2/ electric quadrupole transition at 729 nm with a natural linewidth below 1 Hz serves as clock transition, while laser cooling on one of the resonance lines is carried out at 397 nm. To obtain the small spectral linewidths necessary for a frequency standard performance, it is essential to reduce the residual Doppler broadening caused by the RF heating in the Paul trap. The first-order Doppler broadening of a single ion can be eliminated in the Lamb-Dicke regime where the ion's amplitude of motion is inferior to the emitted wavelength. The main condition for the access of this frequency modulation regime is a high motional frequency of the trapped ion. This is more easily obtained in a low capacitance device and thus traps with reduced dimensions are required. We have set up a miniature ion trap of the Paul-Straubel-type. The stored ions are observed by a photomultiplier in the photon-counting mode as well as by an intensified CCD camera, permitting the visualization of their spatial behavior. Laser cooling of the Ca/sup +/ ions is carried out on the 4S/sub 1/2/-4P/sup 1/2/ resonance line at 397 nm. Progress on the characterization of the trapped single ion as well as on the generation of the involved wavelengths exclusively by solid-state lasers is reported.
Collisional relaxation and fine-structure mixing rate constants have been measured for the metastable DDD doublet (3D3/2,{(3D}_{3/2},(3D3/2​, 3D5/2){3D}_{5/2})3D5/2​) of Ca+{\mathrm{Ca}}^{+}Ca+ ions in the presence of different neutral gases completing a previous work. Experimental results are given for He, Ne, Ar, H2,{\mathrm{H}}_{2},H2​, N2,{\mathrm{N}}_{2},N2​, and CH4.{\mathrm{CH}}_{4}.CH4​. These data have been obtained with a cloud of approximately 105{10}^{5}105 Ca+{\mathrm{Ca}}^{+}Ca+ ions stored in a Paul trap at kinetic energies of around 1 eV. The investigated levels were populated by direct excitation of the corresponding $4S\ensuremath{-}3D$ transitions. The involved time constants were determined from the temporal evolution of the fluorescence of one of the resonance transitions, following the optical pumping of the PPP level from the DDD component. Comparison of our data with other similar experimental and theoretical work is finally presented.
The National Institute of Information and Communications Technology in Japan is proceeding with development of an optical frequency standard using an electric quadrupole transition of Ca+ ions in a small radio-frequency trap. The single, trapped 40Ca+ ions are laser cooled to a temperature of <10 mK using extended-cavity diode lasers at 397 nm and 866 nm. In order to measure the electric quadrupole transition, the linewidth of the clock laser diode at 729 nm is reduced to ~66 Hz using an ultra-low-expansion (ULE) cavity. We observed the electric quadrupole transition with a linewidth of ~600 kHz, together with the ionic motional sidebands. We are also developing optical frequency combs without photonic fibers broadening the spectrum. The experimental is now improved in order to observe the narrower linewidth of the quadrupole transition.
We describe and discuss experiments related to the phenomenon of population trapping of ytterbium ions in the extremely long-lived 4f13 6s2 2F7/2 level. Ion clouds are confined in a radiofrequency trap in the presence of helium buffer gas. The experimental set-up permits electronic ion detection, the observation of resonance fluorescence, and optical excitation at alternating wavelengths to excite either the 2S1/2–2P1/2 resonance transition, or transitions of similar wavelength which provide optical deexcitation of ions from the 2F7/2 level to the ground state. The observed dependence of the population trapping rates on helium pressure is attributed to the effect of fine structure mixing collisions. The transitions which deexcite ions from the 2F7/2 state show Lorentzian lineshapes with widths of 6–10 GHz and resonance wavelengths which are in significant disagreement with tabulated level positions.
Abstract —We are proceeding with a development of an optical frequency standard using a 2 S 1/2 – 2 D 5/2 electric quadrupole transition of Ca + ions in a small radio-frequency trap. We have theoretically confirmed that an uncertainty of <1 x 10 -15 is attainable in measurement of the 2 S 1/2 – 2 D 5/2 transition frequency. Experimentally, we have developed stable laser-diode systems and observed the quantum jump of single 40 Ca + ions to the 2 D 5/2 state. I. I NTRODUCTION The uncertainty of primary frequency standards using Cs atoms reaches around 10 -15 and the inherent limits involved in them are discussed. On the other hand, frequency standards using new materials and methods are proposed for developing more accurate frequency standards. Recently, several groups have measured frequencies of the ionic forbidden transitions in the optical region to apply them to the clock transitions of optical frequency standards [1]. We now proceeds with study on an optical frequency standard using single Ca