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.
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.
In this thesis, the study of cold gases of neon atoms in different metastable states is described. It contains measurements of the collisional parameters for both the 3s[3/2]2 and the 3s'[1/2]0 metastable state and the dependence of the inelastic loss on external fields. Furthermore, the investigation of frequency dependent laser-induced collisions, and the possibility to excite photoassociation resonances is presented. Based on previous measurements we have selected 22Ne for evaporative cooling. Although, we can experimentally achieve an increase in phase-space density with evaporative cooling, the relatively high inelastic collision parameters prevent the realization of a Bose-Einstein condensate in neon. For the measurements described here, neon atoms have been confined in a magneto-optical trap, in a magnetostatic trap, or in an optical dipole trap, respectively. By laser cooling inside the magnetic trap, atomic samples with more than 95 percent occupation of the magnetic substate m=+2 could be prepared. They have a typical temperature of 0.5 mK, central densities up to 1e11 cm^-3, and a central phase-space density of up to 2.2e-7. After loading the optical dipole trap from the magnetic trap, 2.5e6 atoms with typical temperatures of 0.1 mK, and central densities up to 5e10 cm^-3 were trapped. By evaporative cooling of the atoms in the magnetic trap we could increase the phase-space density by a factor of 200 to 5e-5. Also simulations of optimized evaporation for our experimental parameters show clearly that we are limited to a phase-space density on the order of 1e-5. From these simulations it became clear that a 5-fold increase in the good-to-bad ratio for evaporative cooling suffices to reach the quantum degenerate regime. Investigating the frequency dependence of laser-induced collisions did not reveal an experimental signature for the excitation of photoassociation resonances. For the 3D3 line a frequency dependence of laser enhanced Penning ionization was observed, which is interesting in itself. The absence of the collisional enhancement effect by laser light for the transition to the 3D2 line is intriguing and for an explanation calculations are required. Measurement of the two-body loss coefficient as function of the magnetic field showed a field dependence of the inelastic loss. These losses increase towards both small and large offset fields. In the magnetic trap, we are limited to offset fields < 50 G. In this range of fields, the two-body losses are too large to achieve a Bose-Einstein condensate of magnetically trapped metastable neon. The implementation of an optical dipole trap allowed us to trap the 3P0 metastable state. From the trap loss measurements we determined the two-body loss coefficient of the 3P0 metastable state for both bosonic isotopes 20Ne and 22Ne. For 20Ne we obtained s=6(+5,-4)e-10 cm^3/s and for 22Ne s=11(+7,-6)e-10 cm^3/s. These large two-body losses make it extremely unlikely to reach degeneracy with this metastable state. Nevertheless it is important that the 3P0 metastable state can be trapped to investigate other interesting physical effects. For example, it is essential to apply the STIRAP technique for trapped atoms and to realize the proposed coherent control of collisions. There is also a large interest in a precise determination of the lifetime of this metastable state, which is of importance for the verification of QED. We can also trap neon atoms in their energetically lowest magnetic substate 3P2(m=-2) with the perspective of reducing inelastic collisions in the energetically lowest state.
This thesis describes the work done over the past three and a half years on the new metastable helium experiment at the Institut d'Optique in Palaiseau. In the first chapter it describes a study to improve both the efficiency and the accuracy of the Microchannel Plate (MCP) detection system. We have experimented with adding a gold layer on the top of the input plate, something that we have found increases the efficiency but also decreases the accuracy. The addition of a voltage between the two stacked plates has been shown to both raise the efficiency and improve the accuracy in non-coated MCPs.The second chapter is devoted to the construction of the experimental apparatus. Here the excitation of ground state helium to its metastable state is described, as well as the subsequent collimation and cooling by Zeeman slower of the resulting hot atomic beam. The slowed beam is then captured in a Magneto-Optical Trap, in which we have captured 8x108 atoms.In the third chapter an original study on three-dimensional Doppler cooling in a red-detuned molasses and in the Magneto-Optical trap is presented. The metastable helium system is unique as there is no multiple scattering of photons and there are no sub-Doppler effects. This allows for a never before seen experimental realisation of pure Doppler cooling theory. The fourth chapter describes a study on collisions in a magneto-optical trap of metastable helium. Light-induced Penning collisions are responsible for high trap losses at high intensities and at frequencies close to the transition frequency. We measure the constant rate coefficient to Ksp = 2.8 ± 0.4 x 10-7cm3/s.
This paper presents detailed characteristics of an ultra-cold bright metastable neon atomic beam which we have been using for atom-interferometric applications. The basis of the device is an atomic beam released from a magneto-optical trap (MOT) which is operated with a high intensity trapping laser, high magnetic quadrupole field, and large laser detuining. Mainly due to the complex structure of three dimensional magnetic field and laser beams, a bright small spot of atoms is formed near the center of the quadrupole magnetic field under an appropriate operating condition. We obtained the minimum trap diameter of 50 micron meter, the atomic density nearly 10^{13}cm^{-3}, and the atomic temperature slightly less than the Doppler limited temperature of 200 micro-K. By releasing trapped atoms we obtained an bright cold atomic beam which is not far from the collision limited atomic density.
We present an experimental study of the loading of a magneto-optical trap (MOT) from a brightened and slowed beam of metastable neon atoms. The unprecedented high numbers of $9\ifmmode\times\else\texttimes\fi{}{10}^{920}\mathrm{Ne}$ and $3\ifmmode\times\else\texttimes\fi{}{10}^{9}$ 22Ne metastable atoms are trapped under unconventional trap conditions as compared to metastable helium traps, such as low intensity and small detuning. These cause the MOT to have an extraordinarily large volume on the order of 1cm3 and a typical peak density of 1010atoms/cm3. A simple Doppler model is discussed which explains why the optimum is found under these conditions. The model includes the seventh beam necessary for the last slowing step before loading.
This thesis presents investigations into the collision dynamics of cold metastable neon atoms in a magneto-optical trap (MOT). At very cold temperatures (approx. 1 mK) the atomic interaction occurs at long range and cannot be treated classically as the interaction between two nuclear point particles. In addition, the collision dynamics can be considerably altered in the presence of an optical eld. In this thesis results are presented for collisions that are altered by the presence of an optical eld and also collisions where the optical eld can be neglected. Controlled optical collisions of cold, metastable Ne atoms are performed by using a control laser tuned close to the (3s)3P2 to (3p)3D3 cooling transition. The control laser modies the rate of ionizing collisions by promoting a pair of colliding atoms onto an excited state potential. In order to induce collisions between pairs of trapped metastables, a control laser is tuned to the red of the transition where we measure a factor of 4 increase in the rate for ionizing collisions. We also investigate the eect of optical shielding by tuning the laser to the blue of the transition and observe a factor of 5 suppression in the ionization rate. However, the measured ionization spectrum does not contain resonances due to the formation of photoassociated molecules as predicted by Doery et al [1]. Instead, we observe a broad unresolvable ionization spectrum that is well described by established theory [2]. Collision cross sections are measured for neon in the (3s)3P2 metastable state with ground state, thermal atoms and molecules. The technique is based on the measurement of the loss rate due to collisions with a background gas. Generally, these type of collisions are considered undesirable, however, it is possible to infer information about the collision cross section if the rate of collisions is accurately known. This novel technique is described and collision cross section measurements are presented for metastable neon in the (3s)3P2 state with He, Ne, Ar, H2, O2, and N2. The average thermal energy of the collision ranges from 11 meV to 27 meV and the measurements have relatively small errors, of the order of 10%.
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.