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Trapping ultracold argon atoms

P. D. Edmunds

Published Mar 28, 2015• 1 citation
OpenAlex

Abstract

This thesis describes the dipole trapping of both metastable and ground state argon atoms. Metastable argon atoms are first Doppler-cooled down to ∼80 μK in a magneto- optical trap (MOT) on the 4s[3/2]2 to 4p[5/2]3 transitions. These were loaded into dipole traps formed both within the focus of a high-power CO2 laser beam and within an optical build-up cavity. The optical cavity’s well depth could be rapidly modulated: allowing efficient loading of the trap, characterisation of trapped atom temperature, and reduction of intensity noise. Collisional properties of the trapped metastable atoms were studied within the cavity and the Penning and associative losses from the trap calculated. Ground state noble gas atoms were also trapped for the first time. This was achieved by optically quenching metastable atoms to the ground state and then trapping the atoms in the cavity field. Although the ground state atoms could not be directly probed, we detected them by observing the additional collisional loss from co-trapped metastable argon atoms. This trap loss was used to determine an ultra-cold elastic cross section between the ground and metastable states. Using a type of parametric loss spectroscopy we also determined the polarisability of metastable argon at the trapping wavelength of 1064 nm.

Related papers

Trapping Cold Ground State Argon Atoms

P. D. Edmunds, P. F. Barker

We trap cold, ground state argon atoms in a deep optical dipole trap produced by a buildup cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of cotrapped metastable argon atoms and determine an elastic cross section. Using a type of parametric loss spectroscopy we also determine the polarizability of the metastable $4s[3/2{]}_{2}$ state to be $(7.3\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}39}\text{ }\text{ }\mathrm{C}\text{ }{\mathrm{m}}^{2}/\mathrm{V}$. Finally, Penning and associative losses of metastable atoms in the absence of light assisted collisions, are determined to be $(3.3\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$.

arXiv:1406.2503•Physical Review Letters•Oct 30, 2014•13 citations

Creation, trapping and manipulation of a cold argon gas

C. Maher-McWilliams

This thesis describes the construction and characterisation of a unique cold argon atom source for sympathetic cooling of molecules. Argon atoms were laser cooled from their lowest lying metastable state using the 4s[3/2]2 → 4p[5/2]3 transition at 811.5 nm. A magneto-optical trap (MOT) was used to cool the metastable argon (Ar*) atoms to 73.2 ± 0.4 μK and trap them at a density of 3.93 × 10^9 cm-3. Cooling was facilitated using an external-cavity diode laser which was frequency-stabilised to the cooling transition using a magnetic dichroism technique. This was the first application of this technique to a plasma operated at our pressures where the applied magnetic field affected the gas behaviour. The Ar* atoms in the MOT were used to demonstrate chirped optical Stark acceleration for the first time. Atoms were accelerated up to velocities of 191 ± 1 ms-1 while maintaining narrow energy spreads in the accelerated ensemble (30-100 mK). The acceleration occurred over tens of nanoseconds and on micrometre length scales. Control over the number of particles accelerated was achieved by tailoring the depth of the optical lattice potential. Monte Carlo numerical simulations of acceleration were used to fit experimental results and study the dynamics of particles over the acceleration duration. Trapping of Ar* atoms in a quasi-electrostatic trap (QUEST) has also been demonstrated. The QUEST was formed at the focus of a 100 W laser beam with a wavelength of 10.6 μm. A trap lifetime of 18.3 ± 0.3 ms was measured.

•Jan 28, 2013•1 citation

Photoassociative Spectroscopy of Ultracold Metastable Argon and Study of Dual Species Trap Loss in a Rubidium-Metastable Argon MOT

Michael K. Shaffer

This dissertation presents the findings of two experimental investigations in ultracold atomic and molecular physics: The study of the dual species trap loss in a rubidium - metastable argon magneto-optical trap and the photoassociative spectroscopy of ultracold metastable argon. The interspecies trap loss rate coefficients have been measured for ultracold collisions between 85Rb and 40Ar* in a dual-species magneto-optical trap (MOT) and the two rates have been found to be approximately equal over the range of intensities studied with values of β'Rb–Ar* = 3.0 ± 1.3 × 10-11 cm3/s and β'Ar*–Rb = 1.9 ± 0.9 × 10-11 cm3/s where β' Rb–Ar* is the trap loss coefficient for Rb in the presence of Ar* and β'Ar*–Rb is the reciprocal term. In addition, the trap loss rate coefficient for cold collisions in a metastable argon MOT alone have been measured with an average value of β Ar* = 5.2 ± 1.6 × 10-10 cm3/s. Using a quadrupole mass spectrometer, the production of Ar +, Ar+2, Rb+, and RbAr+ ions in the dual MOT have been observed, clearly identifying heteronuclear Penning and associative ionization as trap loss mechanisms. In the second experiment, the first ever investigation of the photoassociative (PA) spectroscopy of Ar* has been made. The exploratory study focuses on PA spectroscopy near the 4s[3/2]2 + 4p[5/2]3 asymptote of the Ar2* diatomic molecule over a 10 GHz range red detuned of the atomic resonance. With a range of probe laser intensities from ∼ 102–105ISat, 12 resonances have been observed. The spectra have been analyzed using the near-dissociation LeRoy-Bernstein method. Through this analysis, the spectra seem to best correlate with excitations to the 5g state.

•Jan 1, 2008•0 citations

Laser Cooling and Trapping of Metastable Neon and Applications to Photoionization

J. P. Ashmore

This thesis presents an in-depth study into the characterization and enhancement of a metastable neon laser cooled and trapped atomic beam. The apparatus consists of a standard Zeeman slowed atomic beam loaded into a magneto-optical trap and was designed for applications to electron scattering experiments and photoionization. The efficiency of the metastable neon atomic source was investigated to determine the ideal cathode type for maximum metastable production and optimal atomic beam velocity haracteristics. A series of characterization measurements were performed on the MOT, and the trap volume and population were investigated for a range of trapping and slowing laser intensities and detunings, together with the MOT and Zeeman slower magnetic fields. The volume measurements were compared to standard Doppler theory and it was found that the Doppler model inadequately explained the trap behaviour. It was found that the MOT population characteristics were governed by two processes: two-body losses that limit the trap population at high densities, and the efficiency of the atom capture process which limits the operational range of the MOT over the various parameters. The trap temperature was determined to be 1.3mK via a time-of-flight technique. This was nearly twice that predicted by Doppler theory and the lack of agreement once again suggests the inadequacies in the Doppler theory to correctly model the experiment. The application of the MOT to the photoionization cross-section measurement of the (2p53p)3D3 state of neon was investigated. The MOT decay technique was utilized to measure cross-section values of o351 = 2.9+0.2 -0.3 x 10 -18cm2 and o363 = 3.1 +0.3 -0.4 x 10-18cm2 at the wavelengths of 351nm and 363nm respectively. This is an increase in accuracy of around a factor of five from previous measurements and it was found that the results agreed well with the values predicted by current theories.

•Jan 1, 2005•2 citations

Interaction of cold metastable neon atoms - towards Bose-Einstein condensation of neon

P. Spodem, Tobias Kraemer, A. Bunkowski +3 more

Summary form only given. The understanding of the interaction of ultracold atoms will be substantially extended by the experimental study of ultracold non-alkaline systems. Due to the special internal structure and the high internal energy, metastable noble gases will play a crucial role. The objective of our work is to attain a detailed study of the atomic structure and the interactions in a gas of ultracold metastable neon atoms. Ensembles of high phase space density and, if possible, Bose condensates shall be achieved. The elementary pair interaction as well as the collective interactions are to be characterized. Of special interest is Penning ionization as it is the main loss process in dense metastable atom traps. The degree of its suppression in a spin polarized gas will strongly affect the feasibility of a quantum-degenerate system of metastable atoms. In addition, metastable noble gas atoms will allow the implementation of novel diagnostics for the investigation of Bose condensates due to their high detectability. We want to make use of this advantage in order to investigate higher order correlation functions and study the laser-like behavior of Bose condensates and atom-laser outputs. We have achieved loading of 4/spl times/10/sup 8/ atoms in a magneto-optical trap (MOT) and after efficient spin polarization of 2.5 /spl times/ 10/sup 8/ atoms in a Ioffe-Pritchard-type magnetic trap. We present a precision measurement of the lifetime of the 3s[3/2]/sub 2/-metastable state of neon which we could determine to 14.70(13)s. We report on the status of the determination of the elastic scattering rate, the rates of Penning ionization for spin-polarized and non-spin-polarized atom samples, and the implementation of evaporative cooling.

European Quantum Electronics Conference (EQEC)•Oct 19, 2004•0 citations

Laser cooling and optical trapping of Ytterbium

S. L. Kemp

This thesis presents the development of an experimental apparatus designed to investigate the ultracold collisional properties for mixtures of Cs and Yb, with a long-term view to the creation of ultracold CsYb molecules via indirect cooling methods. The unpaired electron spin that is inherent to molecules of this form gives rise to a magnetic dipole moment in addition to a ground state electric dipole moment. This enables extra control over molecular interactions and should enable the experimental simulation of spin lattice models. We focus on the implementation of a system designed to controllably laser cool and optically trap Yb. The first step in this system is the production of a magneto-optical trap (MOT) on the triplet 1S0 to 3P1 transition of Yb. With careful control over the cooling beam detunings and power, gravitational-assisted Doppler cooling allows samples of Yb to be prepared at 22 uK. This regime of enhanced Doppler cooling is investigated and proves to be a crucial step to ensuring good transfer of cold Yb to optical traps. The construction and characterisation of single and crossed beam optical dipole traps for Yb are discussed. The single beam optical trap has been used to verify a model for the optical trapping of Yb in its ground state. This trap has also been utilised as a tool for the measurement of the light shift on the 1S0 to 3P1 transition at a wavelength of 1070~nm. In the main experimental sequence, Yb atoms are loaded from the magneto-optical trap into the crossed optical dipole trap, allowing evaporative cooling ramps to quantum degeneracy to be performed. This highly-reproducible system typically forms Bose-Einstein condensates with 2 x 10^5 174Yb atoms. This thesis additionally reports on the progress made towards measurements of the interspecies scattering length for 133Cs and Yb isotopes. We present two approaches that are being developed in tandem: rethermalisation in a conservative trap, and two-photon photoassociation. Progress towards rethermalisation measurements has focussed on developing systems for the efficient transfer of Cs to an optical trap. For photoassociative measurements, a laser system has been developed and tested by producing one-photon photoassociation spectra of Cs2.

•Jan 1, 2017•0 citations
This thesis describes the dipole trapping of both metastable and ground state argon atoms. Metastable argon atoms are first Doppler-cooled down to ∼80 μK in a magneto- optical trap (MOT) on the 4s[3/2]2 to 4p[5/2]3 transitions. These were loaded into dipole traps formed both within the focus of a high-power CO2 laser beam and within an optical build-up cavity. The optical cavity’s well depth could be rapidly modulated: allowing efficient loading of the trap, characterisation of trapped atom temperature, and reduction of intensity noise. Collisional properties of the trapped metastable atoms were studied within the cavity and the Penning and associative losses from the trap calculated. Ground state noble gas atoms were also trapped for the first time. This was achieved by optically quenching metastable atoms to the ground state and then trapping the atoms in the cavity field. Although the ground state atoms could not be directly probed, we detected them by observing the additional collisional loss from co-trapped metastable argon atoms. This trap loss was used to determine an ultra-cold elastic cross section between the ground and metastable states. Using a type of parametric loss spectroscopy we also determined the polarisability of metastable argon at the trapping wavelength of 1064 nm.
We trap cold, ground state argon atoms in a deep optical dipole trap produced by a buildup cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of cotrapped metastable argon atoms and determine an elastic cross section. Using a type of parametric loss spectroscopy we also determine the polarizability of the metastable 4s[3/2]24s[3/2{]}_{2}4s[3/2]2​ state to be $(7.3\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}39}\text{ }\text{ }\mathrm{C}\text{ }{\mathrm{m}}^{2}/\mathrm{V}$. Finally, Penning and associative losses of metastable atoms in the absence of light assisted collisions, are determined to be $(3.3\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$.
This thesis describes the construction and characterisation of a unique cold argon atom source for sympathetic cooling of molecules. Argon atoms were laser cooled from their lowest lying metastable state using the 4s[3/2]2 → 4p[5/2]3 transition at 811.5 nm. A magneto-optical trap (MOT) was used to cool the metastable argon (Ar*) atoms to 73.2 ± 0.4 μK and trap them at a density of 3.93 × 10^9 cm-3. Cooling was facilitated using an external-cavity diode laser which was frequency-stabilised to the cooling transition using a magnetic dichroism technique. This was the first application of this technique to a plasma operated at our pressures where the applied magnetic field affected the gas behaviour. The Ar* atoms in the MOT were used to demonstrate chirped optical Stark acceleration for the first time. Atoms were accelerated up to velocities of 191 ± 1 ms-1 while maintaining narrow energy spreads in the accelerated ensemble (30-100 mK). The acceleration occurred over tens of nanoseconds and on micrometre length scales. Control over the number of particles accelerated was achieved by tailoring the depth of the optical lattice potential. Monte Carlo numerical simulations of acceleration were used to fit experimental results and study the dynamics of particles over the acceleration duration. Trapping of Ar* atoms in a quasi-electrostatic trap (QUEST) has also been demonstrated. The QUEST was formed at the focus of a 100 W laser beam with a wavelength of 10.6 μm. A trap lifetime of 18.3 ± 0.3 ms was measured.
This dissertation presents the findings of two experimental investigations in ultracold atomic and molecular physics: The study of the dual species trap loss in a rubidium - metastable argon magneto-optical trap and the photoassociative spectroscopy of ultracold metastable argon. The interspecies trap loss rate coefficients have been measured for ultracold collisions between 85Rb and 40Ar* in a dual-species magneto-optical trap (MOT) and the two rates have been found to be approximately equal over the range of intensities studied with values of β'Rb–Ar* = 3.0 ± 1.3 × 10-11 cm3/s and β'Ar*–Rb = 1.9 ± 0.9 × 10-11 cm3/s where β' Rb–Ar* is the trap loss coefficient for Rb in the presence of Ar* and β'Ar*–Rb is the reciprocal term. In addition, the trap loss rate coefficient for cold collisions in a metastable argon MOT alone have been measured with an average value of β Ar* = 5.2 ± 1.6 × 10-10 cm3/s. Using a quadrupole mass spectrometer, the production of Ar +, Ar+2, Rb+, and RbAr+ ions in the dual MOT have been observed, clearly identifying heteronuclear Penning and associative ionization as trap loss mechanisms. In the second experiment, the first ever investigation of the photoassociative (PA) spectroscopy of Ar* has been made. The exploratory study focuses on PA spectroscopy near the 4s[3/2]2 + 4p[5/2]3 asymptote of the Ar2* diatomic molecule over a 10 GHz range red detuned of the atomic resonance. With a range of probe laser intensities from ∼ 102–105ISat, 12 resonances have been observed. The spectra have been analyzed using the near-dissociation LeRoy-Bernstein method. Through this analysis, the spectra seem to best correlate with excitations to the 5g state.
This thesis presents an in-depth study into the characterization and enhancement of a metastable neon laser cooled and trapped atomic beam. The apparatus consists of a standard Zeeman slowed atomic beam loaded into a magneto-optical trap and was designed for applications to electron scattering experiments and photoionization. The efficiency of the metastable neon atomic source was investigated to determine the ideal cathode type for maximum metastable production and optimal atomic beam velocity haracteristics. A series of characterization measurements were performed on the MOT, and the trap volume and population were investigated for a range of trapping and slowing laser intensities and detunings, together with the MOT and Zeeman slower magnetic fields. The volume measurements were compared to standard Doppler theory and it was found that the Doppler model inadequately explained the trap behaviour. It was found that the MOT population characteristics were governed by two processes: two-body losses that limit the trap population at high densities, and the efficiency of the atom capture process which limits the operational range of the MOT over the various parameters. The trap temperature was determined to be 1.3mK via a time-of-flight technique. This was nearly twice that predicted by Doppler theory and the lack of agreement once again suggests the inadequacies in the Doppler theory to correctly model the experiment. The application of the MOT to the photoionization cross-section measurement of the (2p53p)3D3 state of neon was investigated. The MOT decay technique was utilized to measure cross-section values of o351 = 2.9+0.2 -0.3 x 10 -18cm2 and o363 = 3.1 +0.3 -0.4 x 10-18cm2 at the wavelengths of 351nm and 363nm respectively. This is an increase in accuracy of around a factor of five from previous measurements and it was found that the results agreed well with the values predicted by current theories.
Summary form only given. The understanding of the interaction of ultracold atoms will be substantially extended by the experimental study of ultracold non-alkaline systems. Due to the special internal structure and the high internal energy, metastable noble gases will play a crucial role. The objective of our work is to attain a detailed study of the atomic structure and the interactions in a gas of ultracold metastable neon atoms. Ensembles of high phase space density and, if possible, Bose condensates shall be achieved. The elementary pair interaction as well as the collective interactions are to be characterized. Of special interest is Penning ionization as it is the main loss process in dense metastable atom traps. The degree of its suppression in a spin polarized gas will strongly affect the feasibility of a quantum-degenerate system of metastable atoms. In addition, metastable noble gas atoms will allow the implementation of novel diagnostics for the investigation of Bose condensates due to their high detectability. We want to make use of this advantage in order to investigate higher order correlation functions and study the laser-like behavior of Bose condensates and atom-laser outputs. We have achieved loading of 4/spl times/10/sup 8/ atoms in a magneto-optical trap (MOT) and after efficient spin polarization of 2.5 /spl times/ 10/sup 8/ atoms in a Ioffe-Pritchard-type magnetic trap. We present a precision measurement of the lifetime of the 3s[3/2]/sub 2/-metastable state of neon which we could determine to 14.70(13)s. We report on the status of the determination of the elastic scattering rate, the rates of Penning ionization for spin-polarized and non-spin-polarized atom samples, and the implementation of evaporative cooling.
This thesis presents the development of an experimental apparatus designed to investigate the ultracold collisional properties for mixtures of Cs and Yb, with a long-term view to the creation of ultracold CsYb molecules via indirect cooling methods. The unpaired electron spin that is inherent to molecules of this form gives rise to a magnetic dipole moment in addition to a ground state electric dipole moment. This enables extra control over molecular interactions and should enable the experimental simulation of spin lattice models. We focus on the implementation of a system designed to controllably laser cool and optically trap Yb. The first step in this system is the production of a magneto-optical trap (MOT) on the triplet 1S0 to 3P1 transition of Yb. With careful control over the cooling beam detunings and power, gravitational-assisted Doppler cooling allows samples of Yb to be prepared at 22 uK. This regime of enhanced Doppler cooling is investigated and proves to be a crucial step to ensuring good transfer of cold Yb to optical traps. The construction and characterisation of single and crossed beam optical dipole traps for Yb are discussed. The single beam optical trap has been used to verify a model for the optical trapping of Yb in its ground state. This trap has also been utilised as a tool for the measurement of the light shift on the 1S0 to 3P1 transition at a wavelength of 1070~nm. In the main experimental sequence, Yb atoms are loaded from the magneto-optical trap into the crossed optical dipole trap, allowing evaporative cooling ramps to quantum degeneracy to be performed. This highly-reproducible system typically forms Bose-Einstein condensates with 2 x 10^5 174Yb atoms. This thesis additionally reports on the progress made towards measurements of the interspecies scattering length for 133Cs and Yb isotopes. We present two approaches that are being developed in tandem: rethermalisation in a conservative trap, and two-photon photoassociation. Progress towards rethermalisation measurements has focussed on developing systems for the efficient transfer of Cs to an optical trap. For photoassociative measurements, a laser system has been developed and tested by producing one-photon photoassociation spectra of Cs2.